Patent Publication Number: US-10769971-B2

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/049,571, filed on Jul. 30, 2018, now U.S. Pat. No. 10,410,549, which claims the benefit of earlier filing date and right of priority to Korean Patent Application Nos. 10-2018-0063203, filed on Jun. 1, 2018 and 10-2018-0088874, filed on Jul. 30, 2018, the contents of which are all hereby incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a display device. 
     BACKGROUND 
     As the information society develops, the demand for display devices is increasing in various forms. In recent years, various display devices such as liquid crystal display device (LCD), plasma display panel (PDP), electro luminescent display (ELD), and vacuum fluorescent display (VFD) have been studied and used. 
     A display device using an organic light emitting diode (OLED) is superior to a liquid crystal display device in terms of luminance characteristics and viewing angle characteristics, and does not require a backlight unit, thereby realizing an ultra-thin display device. 
     The flexible display may be bent or rolled around the roller. A flexible display may be used to implement a display device that is unfoldable or rollable around a roller as needed. At this time, there is a problem that the flexible display is stably rolled around or unrolled from the roller. 
     SUMMARY 
     Embodiments provide a display device capable of sensing the height of a flexible display with high reliability and high accuracy. 
     A display device according to an embodiment of the present invention includes: a housing; a roller disposed in the housing; a flexible display configured to be rolled around the roller; an upper assembly coupled to an upper portion of the flexible display; a lift assembly comprising: a motor; a first arm coupled to the upper assembly; a second arm coupled to the first arm and configured to be pivotably raised in response to operation of the motor; a main gear configured to rotate in response to pivoting of the second arm; a driven gear engaged with the main gear; and a first sensor configured to detect an angle of the second arm based on a rotation of the driven gear, wherein the detected angle of the second arm based on the rotation of the driven gear is used to determine a vertical position of the upper assembly. 
     Wherein the lift assembly further comprises a biasing member configured to apply a biasing force to the upper assembly in a first direction for extending the flexible display away from the housing. 
     The display device further comprises a first magnetic member configured to magnetically engage the biasing member with the upper assembly. 
     Wherein the first magnetic member is disposed at a top surface of the biasing member. 
     Wherein the first magnetic member is disposed at the upper assembly. 
     Wherein the lift assembly further comprises a second magnetic member disposed at a stationary member and configured to magnetically engage with the upper assembly when the upper assembly contacts the stationary member. 
     Wherein the lift assembly further comprises a second magnetic member configured to magnetically engage with the upper assembly when the upper assembly is in a retracted position. 
     Wherein the stationary member comprises: a horizontal surface configured to contact a lower surface of the upper assembly; and a vertical member extending adjacent to the horizontal surface to prevent lateral movement of the upper assembly, wherein the second magnetic member is disposed at the horizontal surface. 
     Wherein as the upper assembly is moved to a retracted position, the upper assembly contacts the biasing member and thereafter contacts the stationary member. 
     Wherein the upper assembly is configured to move the biasing member in a second direction opposite the first direction as the upper assembly is moved to a retracted position; and the display further comprises a second sensor configured to detect a position of the biasing member, wherein the detected position of the biasing member is used with the detected angle of the second arm to determine the vertical position of the upper assembly. 
     The display device of claim  1 , further comprises a controller configured to determine the vertical position based on the detected angle. 
     According to an embodiment of the present invention, the height of the flexible display may be reliably sensed, and the height of the flexible display may be controlled with higher accuracy. 
     In addition, the number of sensing values may be increased by the gear ratio of the main gear and the driven gear, and the rotation angle of the arm shaft and the second arm may be sensed with higher accuracy. 
     In addition, even when an external force is applied to the flexible display and thus the height of the flexible display is changed, the height of the flexible display may be calculated with high reliability. 
     Furthermore, it is possible to minimize the impact or noise which may occur when the flexible display is lowered. 
     Moreover, the flexible display may be reliably lowered to the maximum lowering height. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a display device according to an embodiment of the present invention. 
         FIG. 2  is a side view illustrating operation examples of the display device according to an embodiment of the present invention. 
         FIG. 3  is a cross-sectional view illustrating the inside of a housing in  FIGS. 1 and 2 . 
         FIG. 4  is a perspective view when a lift assembly lowers a flexible display, according to an embodiment of the present invention. 
         FIG. 5  is a perspective view when the lift assembly lifts the flexible display, according to an embodiment of the present invention. 
         FIG. 6  is a perspective view when the lift assembly lifts the flexible display to the highest height, according to an embodiment of the present invention. 
         FIG. 7  is an enlarged rear view of an angle sensor module according to an embodiment of the present invention. 
         FIG. 8  is a partial cut-out perspective view of the angle sensor module according to an embodiment of the present invention. 
         FIG. 9  is a rear view illustrating an upper bracket, an biasing member, and a stationary member when the upper bracket is lowered, according to the embodiment of the present invention. 
         FIG. 10  is a rear view illustrating the upper bracket, the biasing member, and the stationary member when the upper bracket is completely lowered, according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a perspective view of a display device according to an embodiment of the present invention,  FIG. 2  is a side view illustrating operation examples of the display device according to an embodiment of the present invention, and  FIG. 3  is a cross-sectional view illustrating the inside of a housing in  FIGS. 1 and 2 . 
     A display device includes a housing  1 , and a flexible display  2  which is lowered to the housing  1  or lifted above the housing  1 . The flexible display  2  may include a display panel  3  and a display cover  4 . 
     The display device may further include a roller  5 , (see  FIG. 3 ). When the flexible display  2  is lowered, the flexible display  2  is rolled around the roller  5 . The roller  5  may be disposed in the housing  1 . 
     The display device may include a lift assembly  10  which lifts or lowers the flexible display  2 . The lift assembly  10  may be connected to the flexible display  2 , and the flexible display  2  may be lifted or lowered by the lift assembly  10  in a state of being connected to the lift assembly  10 . 
     The display device may have a thickness in a front-back direction (X), have a width in a horizontal direction (Y), and have a height in a vertical direction (Z). 
     The housing  1  may include a combination of a plurality of members. A space S in which the roller  5  is accommodated may be formed in the housing  1 . When the flexible display  2  is lowered, the flexible display  2  may be accommodated in the space S together with the rollers  5 . When the flexible display  2  is lifted, at least a part of the flexible display  2  may be lifted above the space S. Only a part or all of the flexible display  2  may be lifted above the space S according to the lifted height. 
     The roller  5  may be rotatably accommodated in the interior of the housing  1 . The housing  1  may be provided with a roller supporter  51  (see  FIGS. 4 to 6 ) which rotatably supports the roller  5 . A pair of roller supporters  51  may be provided in the housing  1 , and the roller  5  may be rotatably supported to the pair of roller supporters  51  between the pair of roller supporters  51 . The roller  5  may include a rotational shaft  52  (see  FIG. 3 ) rotatably supported to the roller supporter  51 . The roller  5  may include a roller body  53  (see  FIG. 3 ) around which the flexible display  2  is rolled. The roller body  53  is connected to the rotational shaft  52  and may be rotated around the rotational shaft  52 . 
     The flexible display  2  may be connected to the roller body  53 . When the roller body  53  is rotated about the rotational shaft  52 , the flexible display  2  may be rolled around or unrolled from the roller body  53  in a state of being connected to the roller body  53 . 
     The housing  1  may be provided with a roller rotation mechanism (not illustrated) which rotates the roller  5  in the forward and reverse directions. The roller rotation mechanism may include a power source such as a motor, and may be connected to the rotational shaft  52  of the roller  5  to rotate the roller  5 . The roller rotation mechanism may be accommodated in the space S of the housing  1  together with the roller  5 . The roller rotation mechanism may include a motor connected to the rotational shaft  52  of the roller  5 . The roller rotation mechanism may include a motor having a driving shaft, a belt for transmitting the driving force of the motor to the rotational shaft  52  of the roller  5  between the driving shaft of the motor and the rotational shaft  52  of the roller  5 , and a power transmission member such as a pulley or a power transmission member such as a gear or a link. 
     In the display device, the roller  5  may be rotated while the flexible display  2  is rolled around or unrolled from the roller  5  when the flexible display  2  is lifted or lowered, without a separate roller rotation mechanism. 
     The housing  1  may include a front cover  11  covering the rollers  5  in front of the rollers  5 . The front cover  11  may form the front surface appearance of the housing  1 . 
     The housing  1  may further include at least one side cover  12  which covers the roller  5  on the side of the roller  5 . The side cover  12  may form the side surface appearance of the housing  1 . A pair of side covers  12  may be provided, and the pair of side covers  12  may include a left cover positioned on the left side of the roller  5  and a right side cover positioned on the right side of the roller  5 . 
     The housing  1  may be provided with an opening  13  (see  FIG. 3 ) through which the flexible display  2  passes. The housing  1  may further include a top cover  14  which forms an upper surface appearance. The opening  13  may be formed in the top cover  14  so as to be vertically opened. 
     The display device may include a housing door  20  which opens and closes the opening  13 . The housing door  20  may be disposed in the top cover  14  so as to extend or retract horizontally to open or close the opening  13 , or may be arranged to be rotated in the vertical direction. The housing door  20  may be positioned in the opening  13  to close the opening  13  when all of the flexible display  2  is inserted into the space S of the housing  1 , and the housing door  20  may open the opening  13  before at least a part of the flexible display  2  is lifted to the upper side of the housing  1 . 
     The flexible display  2  may be rolled around the roller  5  and all of the flexible display  2  may be accommodated in the space S. At least a part of the flexible display  2  may be unrolled from the roller  5  and lifted above the space S. 
     The thickness of the flexible display  2  may be thinner than the thickness of the housing  1 . The width of the housing  1  may be longer than the width of the flexible display  2 . When the flexible display  2  is unfolded, the height (that is, the top height of the flexible display) may be higher than the height of the housing  1  (that is, the top height of the housing). When the flexible display  2  is maximally lowered, the flexible display  2  may be inserted into the space S of the housing  1  and concealed in the housing  1 , and when at least a part of the flexible display  2  is lifted above the housing  1 , the flexible display  2  may be exposed above the housing  1 . 
     As illustrated in  FIG. 2A , the flexible display  2  may be inserted and accommodated into the housing  1 . As illustrated in  FIG. 2B , only a part of the flexible display  2  may be lifted to a predetermined height H 1  on the upper surface of the housing  1 . As illustrated in  FIG. 2C , the flexible display  2  may be lifted to the maximum lifting height H 2 . 
     The display panel  3  preferably has elasticity such as an OLED or the like that may be bent or rolled. In this case, the display panel  3  may be a flexible display panel. 
     The display panel  3  may display an image through its front surface. A region of the display panel  3  which is exposed to the upper side of the housing  1  may be an active region in which an image may be seen from the outside. The region of the display panel  3  positioned in the space S of the housing  1  may be an inactive area in which no image may be seen from the outside. 
     The display cover  4  may be disposed on the back surface of the display panel  3  and may cover the back surface of the display panel  3 . 
     The display cover  4  may be rolled around the roller  5  together with the display panel  3 . The display cover  4  may be configured to support the display panel  3 . The display cover  4  may have a higher strength than the display panel  3 . 
     The front surface of the display cover  4  may be attached to the back surface of the display panel  3 . The display cover  4  may be attached to the back surface of the display panel  3  by an adhesive means such as a double-sided tape or the like and may be integrated with the display panel  3 . 
     The display cover  4  may include a plurality of segments  41 . The segment  41  may also be referred to as an apron. Each of the plurality of segments  41  may be attached to the back surface of the display panel  3 . The plurality of segments  41  may support the other segments positioned on the upper side while being in contact with the adjacent other segments in the vertical direction when the flexible display  2  is lifted. When the flexible display  2  is rolled around the roller  5 , the flexible display  2  may be smoothly rolled around the roller  5  together with the display panel  3  while being spread with the adjacent other segments. 
     An upper assembly may be coupled to an upper portion of the flexible display. The upper assembly may include a connecting bar  48 . The connecting bar  48  may be disposed to be elongated on the upper portion of the display cover  4 . The connecting bar  48  may be fixed to at least one of the display panel  3  and the display cover  4  by a fastening member such as a screw or an adhesive means such as an adhesive. The connecting bar  48  may be connected to the lift assembly  10 , and the flexible display  2  may be lifted and lowered by the connecting bar  48  when the lift assembly  10  lifts the connecting bar  48 . The upper assembly may further include an upper bracket  49 . 
     The lift assembly  10  may be connected to the upper portion of the flexible display  2  via the upper assembly. The lift assembly  10  may lift or lower the flexible display  2 . The lift assembly  10  may be disposed behind the flexible display  2  and may support the flexible display  2  at the rear of the flexible display  2 . The lift assembly  10  may be covered by the flexible display  2  when viewed from the front of the flexible display  2 . 
     The upper portion of the flexible display  2  may be connected to the lift assembly  10  and the lower portion of the flexible display  2  may be connected to the roller  5 . The flexible display  2  may be rolled around the roller  5  between the upper portion connected to the lift assembly  10  and the lower portion connected to the roller  5 . 
     The housing  1  may further include a lift assembly supporter  15  which supports the lift assembly  10 . The lift assembly supporter  15  may be disposed apart from the top cover  13  and the lift assembly  10  may be mounted to the lift assembly supporter  15 . A part of the lift assembly  10  may be lifted above the opening  13  or lowered below the opening  13  together with the flexible display  2  while the lift assembly  10  is mounted on the lift assembly supporter  15 . 
     The lift assembly supporter  15  may be disposed to be accommodated in the space S of the housing  1 . The lift assembly supporter  15  may include a lower plate  16  positioned below the lift assembly  10  and a front plate  17  erected from the lower plate  16 , and may protect the lift assembly  10 . 
     The housing  1  may further include a lower frame  18  on which the lift assembly supporter  15  is disposed. The lower frame  18  may be horizontally disposed to be elongated between the pair of side covers  12 . The lower frame  18  may be connected to the pair of side covers  12 . The lift assembly supporter  15  may be disposed on the lower frame  18  and may be supported by the lower frame  18 . 
     The housing  1  may further include a back cover  19  which covers a portion of the lift assembly  10  accommodated in the space S of the housing  1 . 
     The lift assembly  10  may include a pair of arms  911  and  912 . The lift assembly  10  may further include an arm joint  913  connected to each of the pair of arms  911  and  912 . 
     The pair of arms  911  and  912  may include a first arm  911  and a second arm  912 . When one of the first arm  911  and the second arm  912  is rotated, the other may be connected to interlock and rotate. 
     Each of the first arm  911  and the second arm  912  may be rotatably connected to the arm joint  913 . A driven gear  916  may be formed on the first arm  911 , and a driving gear  917  may be formed on the second arm  912 . The driving gear  917  is engaged with the driven gear  916  to rotate the driven gear  916 . 
     Upon rotation of the second arm  912 , the driving gear  917  may rotate the driven gear  916  in engagement with the driven gear  916 . Upon rotation of the driven gear  915 , the first arm  911  may be rotated about the driven gear  916 . 
     The first arm  911  may be rotatably connected to the upper assembly. The first arm  911  may be a driven arm which lifts and lowers the upper portion of the flexible display  2  while relatively rotating with the second arm  912 . The driven arm may be connected directly to the flexible display  2  and may be connected to the flexible display  2  through a separate upper bracket  49 . 
     When the second arm  912  rotates, the first arm  911  lifts and lowers the connecting bar  48  and the flexible display  2  may be lifted and lowered. 
     The first arm  911  may be rotatably connected to the connecting bar  48  and may be rotatably connected to the connecting bar  48  on the upper bracket  49 . The upper bracket  49  may be fastened to the connecting bar  48  with a fastening member such as a screw. The upper portion of the first arm  911  may be connected to the connecting bar  48  or the upper bracket  49  by a hinge pin. 
     The lower portion of the first arm  911  may be rotatably connected to the upper portion of the arm joint  913 . The lower portion of the first arm  911  may be connected to the upper portion of the arm joint  913  by a hinge pin. 
     The driven gear  916  may be formed below the first arm  911 . 
     The second arm  912  may be a driving arm which rotates the first arm  911 . The second arm  912  may be connected to the first arm  911  to rotate the first arm  911 . The second arm  912  may be rotatably connected to the lower portion of the arm joint  913 . The upper portion of the second arm  912  may be connected to the lower portion of the arm joint  913  by a hinge pin. The driving gear  917  engaged with the driven gear  916  may be formed on the upper portion of the second arm  912 . 
     The second arm  912  is coupled to the first arm  211  and is pivotably raised in response to operation of a motor  810 . 
     The second arm  912  may be rotatably supported on the housing  1 . The second arm  912  may be rotatably connected to the lift assembly supporter  15  and may be rotatably connected to the separate arm supporters  920  and  921 . 
     The arm supporters  920  and  921  may be mounted on the lift assembly supporter  15 , and may rotatably support the second arm  912  in a state of being vertically erected on the lift assembly supporter  15 . 
     The second arm  912  may be connected to an arm shaft P (see  FIG. 3 ), which is a rotation center shaft of the second arm  912 , and the second arm  912  may be rotated around the arm shaft P. The arm shaft P may be a horizontal shaft connected to the second arm  912 , and may be arranged to be elongated in the front-back direction. The arm shaft P may be fastened to the second arm  912  so as to rotate integrally with the second arm  912  when the second arm  912  rotates. 
     The arm shaft P may be formed separately from the second arm  912  and then coupled to the second arm  912 , or may integrally protrude from the second arm  912 . 
     The arm shaft P may be rotatably supported by the arm supporters  920  and  921 . A pair of arm supporters  920  and  921  may be provided, and the arm shaft P may be rotatably supported by the pair of arm supporters  920  and  921 . 
     One of the pair of arm supporters  920  and  921  may be a first arm supporter mounted on the lift assembly supporter  15 , the other of the pair of arm supporters  920  and  921  may be a second arm supporter mounted on the first arm supporter. A space in which a part of the second arm  912  is rotatably accommodated may be formed between the pair of arm supporters  920  and  921 . The first arm supporter and the second arm supporter may be fastened by a fastening member such as a screw. 
     The pair of arm supporters  920  and  921  may be formed with through-holes through which the arm shaft P rotatably passes, and an arm shaft supporter such as a bearing for supporting the arm shaft P may be disposed in the through-hole. 
     When the second arm  912  is rotated about the arm shaft P, the second arm  912  may be rotated perpendicularly or substantially perpendicularly. The arm shaft P may rotatably connect the lower portion of the second arm  912  to the arm supporters  920  and  921 . 
     The first arm  911  and the second arm  912  may be folded or unfolded while being connected to the arm joint  913 . When the second arm  912  is rotated horizontally or substantially horizontally to the housing  1 , the first arm  911  is horizontally or substantially horizontally laid down like the second arm  912  in a state of being connected to the arm joint  913 . On the other hand, when the second arm  912  is rotated perpendicularly or substantially perpendicularly to the housing  1 , the first arm  911  is erected perpendicularly or substantially perpendicularly like the second arm  912  above the second arm  912 . 
     The display device may further include a rotation mechanism  100  (see  FIGS. 4 to 6 ) which is connected to the second arm  912  to rotate the second arm  912 . The rotation mechanism  100  may include a driving source such as a motor, and at least one power transmission member which transmits the driving force of the driving source to the second arm  912 . 
     The display device may further include a controller  200  which controls the rotation mechanism  100 . The controller  200  may be accommodated in the space S of the housing  1  and may be protected by the housing  1 . The controller  200  may include a main board having a circuit part for controlling the rotation mechanism  100 . The controller  200  may control the driving source of the rotation mechanism  100 . When the controller  200  drives the driving source of the rotation mechanism  100 , the second arm  912  and the first arm  911  are rotated and the flexible display is lifted and lowered by the rotation of the first arm  911 . The controller  200  may control the driving source of the rotation mechanism  100  according to a sensing value of an angle sensor module  1000 . The controller  200  is configured to determine the vertical position of the flexible display  2  based on the detected angle sensed by an angle sensor module  1000   
     The display device may further include the angle sensor module  1000  connected to at least one of the arm shaft P and the second arm  912 . The angle sensor module  1000  may be connected to the controller  200  through a signal line  202 . The sensing value sensed by the angle sensor module  1000  may be transmitted to the controller  200  through the signal line  202 . 
     The angle sensor module  1000  may be accommodated in the space S of the housing  1  and may be protected by the housing  1 . The angle sensor module  1000  may be positioned between the arm supporters  920  and  921  and the housing  1 . The angle sensor module  1000  may be positioned between the arm supporters  920  and  921  and the back cover  19 . The size of the angle sensor module  1000  may be smaller than the size of each of the arm supporters  920  and  921  and the back cover  19 , and may be protected by the arm supporters  920  and  921  and the back cover  19 . The back cover  19  may cover the angle sensor module  1000  and may function as an angle sensor module cover. 
       FIG. 4  is a perspective view when the lift assembly lowers the flexible display, according to an embodiment of the present invention.  FIG. 5  is a perspective view when the lift assembly lifts the flexible display, according to an embodiment of the present invention.  FIG. 6  is a perspective view when the lift assembly lifts the flexible display to the highest height, according to an embodiment of the present invention.  FIG. 7  is an enlarged rear view of the angle sensor module according to an embodiment of the present invention.  FIG. 8  is a partial cut-out perspective view of the angle sensor module according to an embodiment of the present invention. 
     The display device may further include the rotation mechanism  100  which rotates the second arm  912 . The first arm  911 , the second arm  912 , the arm joint  913 , and the rotation mechanism  100  may constitute the lift assembly  10  which lifts and lowering the upper portion of the flexible display  2 . 
     The first arm  911 , the second arm  912  and the arm joint  913  may constitute a link assembly. The link assembly may interlock with the rotation mechanism  100  to lift and lower the flexible display  2 . 
     The display device may include a plurality of link assemblies which are assemblies of the first arm  911 , the second arm  912 , and the arm joint  913 . 
     The plurality of link assemblies L 1  and L 2  are capable of vertically lifting and lowering the flexible display  2  together in a state of being horizontally spaced apart. The rotation mechanism  100  may be connected to each of the plurality of link assemblies L 1  and L 2  and may operate the plurality of link assemblies L 1  and L 2  together. 
     The plurality of link assemblies L 1  and L 2  may include a pair of link assemblies, and the pair of link assemblies may include a left link assembly L 1  and a right link assembly L 2 . The left link assembly L 1  and the right link assembly L 2  may be spaced from each other in the horizontal direction and may be symmetrically arranged in the horizontal direction. 
     When the display device includes both the left link assembly L 1  and the right link assembly L 2 , the first arm  911  of the left link assembly L 1  may be connected to the left upper bracket  49 A mounted on the left side of the connecting bar  48  by a hinge pin, and the first arm  911  of the right link assembly L 2  may be connected to the right upper bracket  49 B mounted on the right side of the connecting bar  48  by a hinge pin. 
     The rotation mechanism  100  may be connected to the second arm  912  to rotate the second arm  912  about the arm shaft P (see  FIGS. 3 and 8 ). The second arm  912  may be formed in a connection part  914  to which the rotation mechanism  100  is connected. The connecting part  914  may be formed between the arm shaft P and the driving gear  918  of the second arm  912 . 
     The rotation mechanism  100  may push or pull the second arm  912  in a state of being connected to the connecting part  914 , and the second arm  912  may be rotated about the arm shaft P when pushed or pulled by the rotation mechanism  100 . When the rotation mechanism  100  pushes the connecting part  914 , the second arm  912  may be erected while rotating about the arm shaft P clockwise or counterclockwise (for example, clockwise). On the contrary, when the rotation mechanism  100  pulls the connecting part  914 , the second arm  912  may be laid down while rotating about the arm shaft P clockwise or anticlockwise (for example, counterclockwise). 
     The rotation mechanism  100  may include at least one motor  810 , a lead screw  840  rotated by the motor  810 , a slider  860  slid along the lead screw  840  during rotation of the lead screw  840 , and a connecting rod  870  connected to the slider  860  and the second arm  912  to push and pull the second arm  912  when the slider  860  slides. 
     When the rotation mechanism  100  rotates the pair of link assemblies L 1  and L 2  together, the rotation mechanism  100  may include at least one motor  810 , a pair of lead screws  840 , a pair of sliders  860 , and a pair of connecting rods  870 . When the display device includes the pair of link assemblies L 1  and L 2 , the lead screw  840 , the slider  860 , and the connecting rod  870  may horizontally symmetrical with respect to the motor  180 . 
     The motor  810  may be installed in the lift assembly supporter  15 . The motor  810  may be a BLDC motor. 
     The driving shaft of the motor  810  may be disposed on both sides of the motor  810 . The right driving shaft and the left driving shaft of the motor  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 lead screw  840  may be connected to the driving shaft of the motor  810  by a coupling  820 . 
     The lead screw  840  may be disposed to penetrate the slider  860 . A thread may be formed on the outer periphery of the lead screw  840 . 
     The rotation mechanism  100  may further include at least one bearing  831  and  832  which supports the lead screw  840 . The bearings  831  and  832  supporting the lead screw  840  may be mounted on the lift assembly supporter  15 . The lead screw  840  may be rotatably supported by the pair of bearings  831  and  832 . The pair of bearings  831  and  832  may be spaced from each other in the longitudinal direction of the lead screw  840 . 
     The slider  860  may be formed with a hollow part through which the lead screw  840  passes. The hollow part of the slider  860  may be formed with a thread engaged with the thread of the lead screw, and may be linearly moved along the lead screw  840  in the longitudinal direction of the lead screw  840  during the rotation of the lead screw  840 . 
     The rotation mechanism  100  may further include a spring  841  which elastically supports the slider  860 . The length of the spring  841  may be shorter than the length of the lead screw  840 . The spring  841  may be disposed between the bearing  831  and the slider  860 . The spring  840  may be disposed between the slider  860  and the bearing  831  closer to the motor  810  among the pair of bearings  831  and  832 . The spring  841  may be disposed so as to surround a part of the outer periphery of the lead screw  840 . One end of the spring  841  may be connected to the bearing  831 , and the other end may be separated from or in contact with the slider  860 . 
     The spring  841  may be pushed and pressed by the slider  860  when the second arm  912  is laid horizontally. When the second arm  912  starts to be erected, the spring  841  may press the slider  860  in a direction opposite to the motor  810  while being restored to an original state. 
     When the restoring force of the spring  841  acts on the slider  860  as described above, the initial load of the motor  810  may be reduced at the time of initial startup of the motor  810  for erecting the second arm  912 . 
     The connecting rod  870  may be formed with a slider connection part connected to the slider  860  by a hinge pin and a second arm connection part connected to the connection part  914  of the second arm  912  by a hinge pin. 
     The slider connection part may be formed on one side of the connecting rod  870  in the longitudinal direction, and the second arm connection part may be formed on the other side of the connecting rod  870  in the longitudinal direction. 
     When the slider  860  is brought close to the motor  810 , the connecting rod  870  may be pulled by the slider  860  and pull the second arm  912  downward, and the second arm  912  may be laid while rotating in a direction approaching the motor  810  with respect to the arm supporters  920  and  921 . 
     On the other hand, when the slider  860  moves away from the motor  810 , the connecting rod  870  may be pushed by the slider  860  and lift the first arm  911 , and the second arm  912  may be erected while rotating in a direction away from the motor  810  with respect to the arm supporters  920  and  921 . 
     The display device may include a sensor module which senses the height of the flexible display  2  as precisely as possible. 
     The flexible display  2  may perform moving control to a height set by a user or a predetermined height. When an external force is applied to the upper end of the flexible display  2  while the power is not supplied to the display device, the flexible display  2  may be stopped after being lowered by an external force, or may be stopped after being lifted. 
     As described above, when power is supplied to the display device in a state in which the height of the flexible display  2  is changed, the changed height of the flexible display  2  needs to be accurately sensed, and the current position (that is, height) of the flexible display  2  needs to be accurately sensed. 
     The driving shaft of the motor  810 , the coupling  820 , the lead screw  840 , the slider  860 , and the connecting rod  870 , the second arm  912 , the arm joint  913 , and the first arm  911  may be a plurality of power transmission members which transmits the driving force of the motor  810  to the flexible display  2 . 
     The display device may calculate the height of the flexible display  2  (that is, the top height of the flexible display  2 ) by sensing the motor  810  or the power transmission members as described above. Hereinafter, the top height of the flexible display  2  will be described as the height of the flexible display  2  for convenience. 
     The sensor module may sense the top height of the flexible display  2 , the top height of the first arm  911 , the rotation angle of the first arm  911 , the height of the female joint  913 , the top height of the second arm  912 , the rotation angle of the second arm  912 , the position of the connecting rod  970 , the position of the slider  860 , the rotation angle of the lead screw  840 , the rotation angle of one of the rotor and the driving shaft of the motor  810 . 
     The sensor module may transmit the sensing value to the controller  200  (see  FIG. 3 ), and the controller  200  may calculate the current height of the flexible display  2  according to the sensing value, 100) and may control the rotation mechanism  100 , in particular, the motor  810 . 
     The sensor module may include a contact-type sensor such as a limit switch or a non-contact-type sensor such as a light sensor or a magnetic sensor. To increase accuracy and reliability, the sensor module preferably includes a non-contact-type sensor. 
     The sensor module is installed in the motor  810  and is capable of detecting the rotation angle of at least one of the rotor and the driving shaft of the motor  810 . However, when the sensor module is installed in the motor  810 , the motor  810  may be made larger. When the rotor is further rotated by inertia of the rotor, it is not easy to accurately sense the rotation angle of the rotor. 
     That is, the sensor module senses the height, the position, or the rotation angle of any one of the power transmission members except for the motor  810 . 
     It is preferable that the sensor module senses the position or the rotation angle of the structure close to the upper end of the flexible display  2  as much as possible among the power transmission members. 
     When the height, the position or the rotation angle of the structure distal from the upper end of the flexible display  2  among the power transmission members are detected, accuracy may be low due to the assembly tolerance of the power transmission members. When the height, the position, or the rotation angle of the structure close to the upper end of the flexible display  2  is sensed, the height of the flexible display  2  may be calculated with a maximum accuracy. 
     That is, it is preferable that the sensor module senses the height, the position, or the rotation angle of one of the first arm  911 , the arm joint  913 , the second arm  912 , and the arm shaft P rather than sensing the position of the slider  860  constituting the rotation mechanism  100  or the rotation angle of the lead screw  840 . 
     On the other hand, the sensor module may be connected to the controller  200  through the signal line  202  (see  FIG. 3 ), and it is preferable to sense the structure having constant position and height during the lifting and lowering of the flexible display  2  among the power transmission members. 
     When the flexible display  2  is lifted to the maximum height as illustrated in  FIG. 2C , each of the first arm  911  and the arm joint  913  may be configured to be lifted above the opening  13  of the housing  1 , the second arm  912  may be configured such that a portion thereof is accommodated within the housing  1 , and the arm shaft P may be configured to be always accommodated in the housing  1 . 
     It is preferable that the sensor module senses the rotation angle of the portion of the second arm  912  which is always positioned in the housing  1 , or senses the rotation angle of the arm shaft P. 
     If the sensor module is connected to the first arm  911  or the arm joint  913 , a portion of the signal line  202  connected to the sensor module may be exposed to the outside through the opening  13  of the housing  1 , and the sensor module may be moved while passing through the opening  13  together with the first arm  911  or the arm joint  913 . 
     On the other hand, when the sensor module senses the rotation angle of the portion of the second arm  912  accommodated in the housing  1  or senses the rotation angle of the arm shaft P, the signal line  202  connected to the sensor module may be always positioned in the space S of the housing  1 , regardless of the height of the flexible display  2 . 
     That is, when sensing the rotation angle of the second arm  912  or sensing the rotation angle of the arm shaft P, the sensor module may acquire a necessary sensing value in a state in which its position and height are not changed. 
     The sensor module may include the angle sensor module  1000  connected to at least one of the arm shaft P and the second arm  912 , and may sense the rotation angle of the arm shaft P and the rotation angle of the second arm  912 . 
     When the second arm  912  rotates, the arm shaft P may be connected to rotate integrally with the second arm  912 . The rotation angle of the second arm  912  and the rotation angle of the arm shaft P are the same. The angle sensor module  1000  may be connected to one of the arm shaft P and the second arm  912 . 
     One example of the angle sensor module  1000  may directly sense the rotation angle of the arm shaft P or the second arm  912 . 
     Another example of the angle sensor module  1000  may increase the number of sensing values by using a pair of gears  1110  and  1120  engaged with a predetermined gear ratio (for example, 4:1 or 7.5:1). 
     The angle sensor module  1000  may include a main gear  1110  connected to the arm shaft P or the second arm  912 , and a driven gear  1120  which is smaller than the main gear  1110  and is rotated upon rotation of the main gear  1110 . The main gear  1110  rotates in response to pivoting of the second arm  912 . The driven gear  1120  is engaged with the main gear  1110 . 
     The main gear  1110  and the driven gear  1120  may be spur gears, and may be engaged with each other so as to rotate in opposite directions. 
     The main gear  1110  may be a large gear larger than the driven gear  1120 , and the driven gear  1120  may be a small gear smaller than the main gear  1110 . 
     The gear ratio of the main gear  1100  and the driven gear  1120  may be 4:1 or 7:5:1. Even if the main gear  1110  is rotated only by about 90° due to the structure of the link assemblies L 1  and L 2 , the driven gear  1120  may be rotated by 360° to 675°. More sensing values may be obtained by the gear ratio of the main gear  1100  and the driven gear  1120 . 
     That is, the angle sensor module  1000  may determine the number of sensing values according to the gear ratio of the main gear  1110  and the driven gear  1120 . As the gear ratio is increased, the rotation angle of the arm shaft P or the second arm  912  may be further segmented and sensed. The rotation angle of the arm shaft P or the second arm  912  may be sensed in units of 0.1°. 
     When the arm shaft P is connected to the main gear  1110 , the arm shaft P may include a main gear fastening part P 11  fastened to the main gear  1110  by a fastening member such as a screw, and the main gear  1110  may be formed with an arm shaft fastening part  1112  fastened to the arm shaft fastening part P 11  by a fastening member such as a screw. The arm shaft fastening part  1112  may be formed at the center of the main gear  1110  and may be the center of rotation of the main gear  1110 . 
     The driven gear  1120  may be rotatably disposed around the main gear  1110 . 
     One example of the driven gear  1120  may have a rotational shaft that is rotatably connected to the arm supporter  920 . 
     Another example of the driven gear  1120  is not rotatably connected to the arm supporter  920 , and may be connected to a shaft  1130  described later and rotated about the shaft  1130 . 
     The angle sensor module  1000  may include a first sensor configured to detect an angle of the second arm  912  based on a rotation of the driven gear  1120 . The detected angle of the second arm  912  can be based on the rotation of the driven gear  1120  is used to determine a vertical position of the upper assembly. 
     The first sensor may include a magnetic sensor which detects the rotation angle of the driven gear  1120  and may include a magnet  1150  which constitutes the magnetic sensor. Even if the height of the flexible display  2  changes while the power is not supplied, the angle sensor module  1000  including the magnet  1150  may detect the current position of the magnet  1150  after power is supplied. 
     The magnet  1150  may be mounted on the driven gear  1120 . In this case, the angle sensor module  1000  may further include a magnet encoder  1160  disposed around the driven gear  1120  to sense the magnet  1150 . When the magnet  1150  is mounted on the driven gear  1120 , the magnet  1150  may be mounted on one surface of both surfaces of the driven gear  1120  facing the magnet encoder  1160 . 
     On the other hand, the angle sensor module  1000  may include a shaft  1130  connected to the driven gear  1120 , a magnet mounter  1140  mounted on the shaft  1130 , a magnet  1150  mounted on the magnet mounter  1140 , and a magnet encoder  1160  which senses the magnet  1150 . 
     When the angle sensor module  1000  includes the shaft  1130 , the driven gear  1120  may be rotated together with the main gear  1110  in a state of being connected to the shaft  1130 . Upon rotation of the main gear  1110 , the driven gear  1120  and the shaft  1130  may be rotated together. 
     The shaft  1130  may be the center shaft of the driven gear  1120  which rotatably supports the driven gear  1120 . The shaft  1130  may be a connector which connects the driven gear  1120  to the magnet mounter  1140 . 
     The magnet mounter  1140  may be rotated integrally with the shaft  1130  when the shaft  1130  rotates. The size of the magnet mounter  1140  may be larger than the size of the shaft  1130 . The magnet mounter  1140  may have an extended shape on one side of the shaft  1130 . The area of the surface on which the magnet  1150  is disposed among both surfaces of the magnet mounter  1140  may be larger than the cross-sectional area of the shaft  1130 . 
     The magnet  1150  may be eccentrically mounted on the magnet mounter  1140 . The magnet  1150  may be disposed between the rotation center of the magnet mounter  1140  and the outer periphery of the magnet mounter  1140 . 
     The magnet encoder  1160  may output the sensing value according to the position of the magnet  1150 . When the shaft  1130  rotates, the magnet  1150  may be rotated about the rotational center axis of the shaft  1130 . The magnet encode  1160  may sense the angle at which the magnet  1160  is rotated by sensing the position of the magnet  1160 . The magnet encoder  1160  may be connected to the controller  200  through the signal line  202  and may transmit the sensing value to the controller  200 . 
     The angle sensor module  1000  may further include a sensor bracket  1170 . 
     The sensor bracket  1170  may be mounted on the arm supporter  920  and  921  or the lift assembly supporter  15 . The sensor bracket  1170  may include a fastening part  1171  fastened to the arm supporters  920  and  921  by a fastening member such as a screw. 
     The sensor bracket  1170  may rotatably support the shaft  1130 . The sensor bracket  1170  may be formed with a through-hole  1172  through which the shaft  1130  passes. The sensor bracket  1170  may further include a shaft supporter  1173 , such as a bearing, disposed between the shaft  1130  and the through-hole  1174 . 
     The sensor bracket  1170  may further include a pair of sidewalls  1174  and  1175  protruding in a backward direction. 
     The magnet encoder  1160  may be seated on a magnet encoder seating jaw  1174 A formed at the rear end of at least one of the pair of sidewalls  1174  and  1175  and fastened to the sensor bracket  1170  by a fastening member  1176  such as a screw. 
     The magnet mounter  1140  and the magnet  1150  may be positioned between the pair of sidewalls  1174  and  1175 . The pair of sidewalls  1174  and  1175  may cover the magnet  1140  and the magnet code  1160  and may protect the magnet  1150 . 
     The sensor bracket  1170  may be formed with a magnet encoder fastening part  1177  in which the magnet encoder  1160  is fastened by the fastening member  1176  such as a screw. The magnet encoder fastening part  1177  may be formed to protrude from the pair of sidewalls  1174  and  1175 . 
     The sensor bracket  1170  may include a combination of a plurality of brackets. In this case, the sensor bracket  1170  may include a first bracket  1170 A which is long in the vertical direction and a second bracket  1170 B which is fastened to the first bracket  1170 A and is long in the horizontal direction. 
     A part of the first bracket  1170 A may be positioned behind the main gear  1110 , and the first bracket  1170 A may protect the main gear  1110 . The fastening part  1171  may be formed on the first bracket  1170 A. 
     A part of the second bracket  1170 B may be positioned behind the main gear  1110 , and the second bracket  1170 B may protect the main gear  1110 . The through-hole  1172 , the pair of sidewalls  1174  and  1175 , and the magnet encoder fastening part  1177  may be formed on the second bracket  1170 B. 
       FIG. 9  is a rear view illustrating an upper bracket, an biasing member, and a stationary member when the upper bracket is lowered, according to the embodiment of the present invention.  FIG. 10  is a rear view illustrating the upper bracket, the biasing member, and the stationary member when the upper bracket is completely lowered, according to the embodiment of the present invention. The lift assembly  10  further comprises a biasing member to apply a biasing force to the upper assembly in a first direction for extending the flexible display  2  away from the housing  1 . biasing member 
     When the flexible display  2  is lowered, one of the connecting bar  48 , the upper bracket  49 , and the first arm  911  may be brought into contact with the upper surface of the biasing member  930  and seated thereon. 
     The biasing member  930  may elastically supports the upper assembly or the first arm  911  when the flexible display  2  is lowered. 
     The biasing member  930  may include a spring  934  seated on the arm supporters  920  and  921  or the lift assembly supporter  15 , and a moving stopper  932  mounted on the spring  934 . 
     Hereinafter, a case where the upper bracket  49  among the connecting bar  48 , the upper bracket  49 , and the first arm  911  is mounted on the biasing member  930  will be described. However, the present invention is not limited to the case where the upper bracket  49  is mounted on the biasing member  930 , and the connecting bar  48  or the first arm  911  may be mounted on the biasing member  930 . 
     The spring  934  may be disposed to be accommodated between the pair of arm supporters  920  and  921 . The lower end of the spring  934  may be connected to one of the pair of arm supporters  920  and  921  and the lift assembly supporter  15 , and the upper end of the spring  934  may be connected to the moving stopper  932 . 
     When an external force is applied to the moving stopper  932  in the downward direction, the spring  934  may be compressed by the moving stopper  932  while absorbing impact applied to the moving stopper  932 . 
     When no external force is not applied to the moving stopper  932  in the downward direction, the spring  934  lifts the moving stopper  932 , and the moving stopper  932  may be in a lifted state, as illustrated in  FIG. 9 . 
     The upper surface of the moving stopper  932  may be directed to the upper bracket  49 . When the upper bracket  49  is lowered, the upper bracket  49  may be mounted on the moving stopper  932 . 
     When the upper bracket  49  is lowered, the upper bracket  49  may press the moving stopper  932  in the downward direction, and the moving stopper  932  may be lowered while compressing the spring  934 . That is, the biasing member  930  may help the upper bracket  49  to be smoothly seated at the maximum lowering height while absorbing impact when the upper bracket  49  is lowered. 
     On the other hand, when the upper bracket  49  is seated on the moving stopper  932  to compress the spring  934  to the maximum, a repulsive force may be applied to the upper bracket  49 . In this case, the upper bracket  49  may jump upward by a repulsive force exerted by the biasing member  930 . 
     In addition, while the second arm  912  is lowered, the power supplied to the motor  810  may be shut off, and the second arm  912  may be further lowered by inertial force. Even in this case, when the spring  934  is compressed to the maximum extent, a repulsive force may be applied to the biasing member  930 . The upper bracket  49  may jump upward by the repulsive force exerted by the biasing member  930 . 
     The display device may fix the position of the upper bracket  49  by using the magnetic force of the magnet. In this case, it is possible to minimize the upward jumping of the upper bracket  49  due to the repulsive force. 
     The display device further comprises a first magnetic member configured to magnetically engage the biasing member with the upper assembly. The first magnetic member may be disposed at a top surface of the biasing member. The first magnetic member may be disposed at the upper assembly. 
     The first magnetic member comprises a magnet M 1  which is disposed on at least one of the upper bracket  49  and the moving stopper  932 . 
     When the magnet M 1  is mounted on the upper bracket  49 , the magnet M 1  may be mounted on the lower portion of the upper bracket  49 . In this case, the magnet M 1  may be mounted on the surface of the upper bracket  49  facing the moving stopper  932 . 
     On the other hand, when the magnet M 1  is mounted on the biasing member  930 , the magnet M 1  may be mounted on the moving stopper  932 . 
     For example, one of the upper bracket  49  and the moving stopper  932  may be a magnetic body, and the other may be a non-magnetic body. In this case, the magnet M may be mounted on the non-magnetic body. When the upper bracket  49  approaches the moving stopper  932  within a predetermined distance, an attractive force may act on the magnet M 1  and the magnetic body. 
     As another example, both the upper bracket  49  and the moving stopper  932  may be a magnetic body, and the magnet M 1  may be mounted on one of the upper bracket  49  and the moving stopper  932 , or may be mounted on each of the upper bracket  49  and the moving stopper  932 . 
     As another example, both the upper bracket  49  and the moving stopper  932  may be a non-magnetic body, and the magnet M 1  may be mounted on each of the upper bracket  49  and the moving stopper  932 . 
     When the magnet M 1  is mounted on each of the upper bracket  49  and the moving stopper  932 , the magnet M 1  mounted on the upper bracket  49  and the magnet M 1  mounted on the moving stopper  932  may be mounted in a direction in which an attractive force acts. 
     On the other hand, the display device may further include a stationary member  940  on which one of the connecting bar  48 , the upper bracket  49 , and the first arm  911  is mounted when the flexible display  2  is maximally lowered. 
     The stationary member  940  may be provided to determine the maximum lowering height of the flexible display  2 . 
     The stationary member  940  may be provided to the arm supporter  920 . The stationary member  940  may be disposed to be elongated in the vertical direction. The stationary member  940  may be fastened to the arm supporter  920  by a fastening member such as a screw or the like, and may integrally protrude from the arm supporter  920 . 
     As the upper assembly is moved to a retracted position, the upper assembly contacts the biasing member and thereafter contacts the stationary member  400 . The upper assembly is configured to move the biasing member in a second direction opposite the first direction as the upper assembly is moved to a retracted position. 
     The display further comprises a second sensor  1190  configured to detect a position of the biasing member  930 . The second sensor  1190  senses the moving stopper  932 . The detected position of the biasing member  930  sensed by the second sensor  1190  is used with the detected angle of the second arm  912  to determine the vertical position of the upper assembly. 
     When the height of the biasing member  930  is lowered by a predetermined height, one of the connecting bar  48 , the upper bracket  49 , and the first arm  911  may be mounted on the stationary member  940 . 
     It is preferable that the upper bracket  49  is seated on the stationary member  940  before the spring  934  of the biasing member  930  is maximally compressed. 
     Hereinafter, it is assumed that the upper bracket  49  among the connecting bar  48 , the upper bracket  49 , and the first arm  911  is mounted on the stationary member  940 . However, the present invention is not limited to the case where the upper bracket  49  is mounted on the stationary member  940 , and the connecting bar  48  or the first arm  911  may be mounted on the stationary member  940 . 
     The stationary member  940  comprises a horizontal surface  942  configured to contact a lower surface of the upper assembly, and a vertical member  944  extending adjacent to the horizontal surface  942  to prevent lateral movement of the upper assembly. 
     The vertical body  944  which prevents the upper bracket  99  mounted on the horizontal surface  942  from moving in the horizontal direction. When the upper bracket  49  is mounted on the horizontal surface  942 , the vertical body  944  may be positioned behind the upper bracket  49 , and the vertical body  944  may prevent the upper bracket  49  from being pushed in the horizontal direction. 
     The lift assembly  10  further comprises a second magnetic member disposed at a stationary member  940  and configured to magnetically engage with the upper assembly when the upper assembly contacts the stationary member  940 . The second magnetic member is configured to magnetically engage with the upper assembly when the upper assembly is in a retracted position. The second magnetic member may be disposed at the horizontal surface  942 . 
     The second magnetic member may comprise a magnet M 2  disposed on at least one of the upper bracket  49  and the stationary member  940 . 
     For example, one of the upper bracket  49  and the stationary member  940  may be a magnetic body, and the other may be a non-magnetic body. The magnet M 2  may be mounted on the non-magnetic body. In this case, when the upper bracket  49  approaches the stationary member  940  within a predetermined distance, an attractive force may be applied to the magnet M 2  and the magnetic body. 
     As another example, both the upper bracket  49  and the stationary member  940  may be a magnetic body, and the magnet M 2  may be mounted on one of the upper bracket  49  and the stationary member  940 , or may be mounted on each of the upper bracket  49  and the stationary member  940 . 
     As another example, both the upper bracket  49  and the stationary member  940  may be a non-magnetic body, and the magnet M 2  may be mounted on each of the upper bracket  49  and the stationary member  940 . 
     When the magnet M 2  is mounted on each of the upper bracket  49  and the stationary member  940 , the magnet M 2  mounted on the upper bracket  49  and the magnet M 2  mounted on the stationary member  940  may be mounted in a direction in which an attractive force acts. 
     As described above, when at least one magnet M 1  and M 2  is included, the controller  200  may cut off the power supplied to the motor  810  before the upper bracket  49  reaches the biasing member  930  or the stationary member  940 . 
     In this case, the upper bracket  49  may be lowered by the inertial force and the gravity even after the power supply is cut off the impact energy is absorbed by the biasing member  930 , so that the noise and the inertial force may be reduced. The upper bracket  49  may be slowly lowered. The position of the upper bracket  49  may be fixed by the attraction of the magnets M 1  and M 2  at a height at which the upper bracket  49  is seated on the stationary member  940 . That is, the flexible display  2  may be smoothly and reliably lowered to the maximum lowering height. 
     When the magnet for fixing the position of the upper bracket  49  and the moving stopper  932  is referred to as a first magnet M 1  and the magnet for fixing the position of the upper bracket  49  and the stationary member  940  is referred to as a second magnet M 2 , the present embodiment may include both the first magnet M 1  and the second magnet M 2 , may include only the second magnet M 2  without including the first magnet M 1 , and may include only the first magnet M 1  without including the second magnet M 2 . 
     In addition, the display device may include the biasing member  930  and the first magnet M 1  without the stationary member  940 , and may include the stationary member  930  and the second magnet M 2  without the biasing member  930 . 
     According to an embodiment of the present invention, the height of the flexible display may be reliably sensed, and the height of the flexible display may be controlled with higher accuracy. 
     In addition, the number of sensing values may be increased by the gear ratio of the main gear and the driven gear, and the rotation angle of the arm shaft and the second arm may be sensed with higher accuracy. 
     In addition, even when an external force is applied to the flexible display and thus the height of the flexible display is changed, the height of the flexible display may be calculated with high reliability. 
     Furthermore, it is possible to minimize the impact or noise which may occur when the flexible display is lowered. 
     Moreover, the flexible display may be reliably lowered to the maximum lowering height. 
     The above description is merely illustrative of the technical idea of the present invention, and various modifications and changes may be made by those skilled in the art without departing from the essential characteristics of the present invention. 
     Therefore, the embodiments disclosed in the present invention are not intended to limit the scope of the present invention, and the scope of the present invention is not limited by these embodiments. 
     The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as falling within the scope of the present invention.