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CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage filing of PCT/KR2015/003730 filed 14 Apr. 2015 and claims the benefit of priority of Korean application no. 10-2014-0117411 filed 4 Sep. 2014, which is hereby incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present technology relates to a rotunda height adjusting device of a boarding bridge, and more particularly, to a rotunda height adjusting device of a boarding bridge for adjusting a height of a rotunda column and distribute a lateral weight. 
     BACKGROUND 
     Because a vertical weight of a rotunda weight adjustable boarding bridge is divided by an inner column and an outer column, only a vertical screw supports a weight of each of a rotunda, a fastened tunnel, and a boarding bridge. 
     Because the vertical screw may bear a wind pressure applied to a side surface of the rotunda and the boarding bridge, and a lateral weight caused by a movement and a stop of the boarding bridge, a size of the vertical screw may increase or a number of vertical screws may increase more than necessary. 
     Thus, development of a rotunda operable in a vertical direction that can endure the lateral weight is required. 
     The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the invention as defined in the claims is to be bound. 
     SUMMARY 
     Technical Goals 
     An aspect of the present invention provides a rotunda height adjusting device of a boarding bridge for distributing a lateral weight to an outer column and an inner column. 
     Another aspect of the present invention provides a rotunda height adjusting device of a boarding bridge for decreasing a size of a vertical screw by disposing a convex rail and a concave rail on an outer column and an inner column in a longitudinal direction. 
     Still another aspect of the present invention provides a stable lubricating oil receiver to minimize a frictional force between a screw and a nut caused by a vertical movement of the screw. 
     Technical Solutions 
     According to an aspect of the present invention, there is provided a rotunda height adjusting device of a boarding bridge, the device for enabling the rotunda to ascend and descend, the device including an outer column configured to ascend and descend to fasten the rotunda, an inner column connected to the outer column and fastened to a ground surface, a vertical screw disposed on a lower end of the rotunda, a nut formed on an inner center portion of the outer column such that the nut is engaged with the vertical screw and corresponds to an external diameter of the vertical screw, and rails disposed on one side of the outer column or one side of the inner column, the rails corresponding to each other and allowing the outer column to ascend and descend, wherein a fastened tunnel is connected to the boarding bridge, and the rails and the nut are configured to distribute a lateral weight. 
     The rails may include a convex rail disposed on an outer side of the inner column and a concave rail disposed on an inner side of the outer column. The convex rail and the concave rail may be disposed in a longitudinal direction and a length of each of the convex rail and the concave rail may correspond to an ascending and a descending distance of the outer column. At least three convex rails may be disposed at an outer side of the inner column. 
     The rotunda height adjusting device may further include a motor and a reducer to rotate the vertical screw. The outer column may ascend and descend by a hydraulic cylinder. 
     The rotunda height adjusting device may further include a lubricating oil receiver configured to contain lubricating oil to decrease a frictional force between the vertical screw and the nut, the lubricating oil receiver disposed to cover an outer surface of the nut. The lubricating oil receiver may be fastened to the inner column. The nut may include at least one hole such that the lubricating oil flows. 
     By maintaining a gap in which an inner column and an outer column are connected and reducing bending of a vertical screw, a lateral weight of a rotunda height adjusting device of a boarding bridge may be distributed. 
     Effects 
     According to an embodiment of the present invention, it is possible to decrease a size of a vertical screw by disposing a convex rail and a concave rail on an outer column and an inner column in a longitudinal direction, such that a number of vertical screws may be minimized and a production cost may be reduced. 
     According to another embodiment of the present invention, it is possible to dispose rails and a nut on a column such that a pressure on a vertical screw may be decreased and the column may ascend and descend in a safe manner. 
     According to still another embodiment of the present invention, it is possible to provide a lubricating oil receiver to minimize a frictional force between a nut and a screw. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. A more extensive presentation of features, details, utilities, and advantages of the present invention as defined in the claims is provided in the following written description of various embodiments of the invention and illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevation view of a movable boarding bridge including a rotunda height adjusting device according to an embodiment; 
         FIG. 2  illustrates a rotunda height adjusting device according to an embodiment; 
         FIG. 3  illustrates rails of an inner column or an outer column according to an embodiment; 
         FIG. 4  illustrates an outer column that ascends and descends by an oil pressure according to an embodiment; and 
         FIG. 5  illustrates a rotunda height adjusting device including a lubricating oil receiver according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an elevation view of a movable boarding bridge  200  including a rotunda height adjusting device  100  according to an embodiment. Description is provided below. 
     The movable boarding bridge  200  includes a rotunda  30  to connect a fastened tunnel  10  and a boarding bridge  20  connected to a passenger terminal, and the rotunda height adjusting device  100  for enabling the rotunda to ascend and descend. 
     Here, the rotunda  30  is included in the rotunda height adjusting device  100  such that the rotunda  30  may rotate and a vertical position of the rotunda  30  may be adjusted. Thus, a position and a height of a gate of an aircraft may correspond to a position and a height of a cabin of the boarding bridge  20 , and the cabin of the boarding bridge  20  may be connected to or disconnected from the gate of the aircraft. 
       FIG. 2  illustrates a rotunda height adjusting device  100 , and  FIG. 3  illustrates rails  41 ,  51  of an inner column  40  or an outer column  50 . Description is provided below. 
     The rotunda height adjusting device  100  may be disposed on a lower end of the rotunda  30 . The rotunda height adjusting device  100  may include an outer column  50 , an inner column  40 , a nut  42 , a vertical screw  72 , a convex rail  41 , a concave rail  51 , a motor  71 , and a reducer  70 . 
     The outer column  50  may be disposed on the lower portion of the rotunda  30  to fasten the rotunda  30 , and the outer column  50  may be fastened to a ground surface. The outer column  50  may be connected to an upper portion of the fastened inner column  40  such that the outer column  50  may ascend and descend. 
     The convex rail  41  may be disposed on an outer surface of the inner column  40  in a longitudinal direction, and the concave rail  51  may be disposed inside of the outer column  50  in a predetermined longitudinal direction. Rails  41 ,  51  of the outer column  50  may be correspondingly formed on each of the upper portion and the lower portion of the fastened inner column  40  such that the outer column  50  may stably move in a vertical direction. 
     The rails  41 ,  51  included in the outer column  50  and the inner column  40  may be correspondingly engaged to each other. The inner column  40  may be cylindrical, and the convex rail  41  may be disposed on the outer surface of the inner column  40 , and a through hole may be formed in a center portion of the inner column  40  and the nut  42  may be disposed in the center portion of the inner column  40 . The concave rail  51  may be included inside of the outer column  50  such that the inner column  40  is inserted. A size and a shape of the nut  42  may correspond to a size and a shape of the vertical screw  72 . 
     It is irrelevant that convex rails  41  and concave rails  51  may be conversely disposed on an inner column  40  and an outer column  50 . 
     Also, an outer column  50  connected to a rotunda  30  and an inner column  40  connected to a ground surface may be conversely disposed based on a site condition. 
     Due to rails  41 ,  51  of the inner column  40  and the outer column  50  disposed in a predetermined longitudinal direction and the nut  42  disposed in the center portion, the outer column  50  including the vertical screw  72  that rotates by the motor  71  and the reducer  70  may ascend and descend to adjust a position of the rotunda  30 . 
     The vertical screw  72  may be disposed on the upper portion of the outer column  50  under the rotunda  30  so that the vertical screw  72  may rotate by a connection of the nut  42  and the vertical screw  72 . 
     The motor  71  may be connected to the reducer  70  and the motor  71  may rotate by an electrical energy and thus, the vertical screw  72  may rotate to adjust the position of the rotunda  30 . 
     The vertical screw  72  may be connected to the nut  42  disposed in the inner column  40  and thus, the vertical screw  72  may ascend and descend. A length of the vertical screw  72  may be formed to reach the nut  42  and the length of the vertical screw  72  may be sufficient to allow the rotunda  30  to ascend and descend. An internal diameter of the nut  42  may correspond to the outer surface of the vertical screw  72 . 
     Hereinafter, detailed description of a movement structure of an inner column and an outer column  50  will be provided. 
     At least three vertical convex rails  41  may be disposed on the outer surface of each of the inner column  40  and the inner column  40 , and a vertical concave rail  51  corresponding to the inner column  40  may be disposed in the outer column  50 . Vertical rails  41 ,  51  that endure a lateral buckling force caused by a vertical movement of the rotunda  30  may be disposed, and a movement length of rails  41 ,  51  may correspond to a stroke of the vertical movement. 
     Also, when a gap is maintained between rails of the inner column  40  and the outer column  50  in which the inner column  40  is connected to the outer column  50  and the vertical screw  72  is bent due to a lateral weight of the boarding bridge  200 , the gap may be maintained to be less than an allowable width of the bent vertical screw  72 . 
     When the lateral weight is applied, a lateral supporting force may be supported by the buckling force of the vertical screw  72  and the rails  41 ,  51  of the inner column  40  and the outer column  50 , and a motion caused by the gap may support and distribute the lateral weight by fastening the vertical screw  72  and the nut  42 . 
       FIG. 4  illustrates an outer column  50  that ascends and descends by an oil pressure according to an embodiment. 
     Besides a configuration of the vertical screw  72  that rotates by the motor  71 , a hydraulic power unit  80  that allows an oil pressure of a hydraulic cylinder  81  to vertically move in a hydraulic pipe  82  may be used in order to allow an outer column to ascend and descend such that a height of the rotunda  30  may be adjusted. 
     A structure of a rail  41 ,  51  may be identical to that of  FIGS. 2 and 3 . The outer column  50  may be disposed on a lower end of the rotunda  30  to fasten the rotunda  30 , and an inner column  40  may be fastened to a ground surface. 
     The outer column  50  may be connected to an upper portion of the fastened inner column  40  such that the outer column  50  may ascend and descend. 
     A convex rail  41  may be disposed on an outer surface of the outer column  50  in a longitudinal direction, and a concave rail  51  may be disposed inside of the outer column  50  in a predetermined longitudinal direction. Rails  41 ,  51  of the outer column  50  may be correspondingly formed on each of the upper portion and the lower portion of the fastened inner column  40  such that the outer column  50  may stably move in a vertical direction. 
     The rails  41 ,  51  included in the outer column  50  and the inner column  40  may be correspondingly engaged to each other. The convex rail  41  may be disposed on the outer surface of the inner column  40  and the concave rail  51  may be disposed inside of the outer column  50  such that the inner column  40  is inserted. In addition, a hydraulic pipe may be included in the inner column  40  or the outer column  50  such that the outer column  50  may ascend and descend by an oil pressure. 
     The rotunda height adjusting apparatus  100  may dispose the convex rail  41  and the concave rail  51  in the outer column  50  and the inner column  40  such that an accurate vertical movement is possible, and the outer column  50  and the inner column  40  may distribute a wind pressure and a lateral weight caused when a boarding bridge  200  is stopped such that a column may ascend and descend in a safe manner. 
       FIG. 5  illustrates a rotunda height adjusting device  100  including a lubricating oil receiver according to an embodiment. A structure of a rail  41 ,  51  may be identical to that of  FIGS. 2 and 3 . An outer column  50  may be disposed on a lower end of a rotunda  30  to fasten the rotunda  30 , and an outer column  50  may be fastened to a ground surface. The outer column  50  may be connected to an upper portion of the fastened inner column  40  such that the outer column  50  may ascend and descend. 
     A convex rail  41  may be disposed on an outer surface of the outer column  50  in a longitudinal direction, and a concave rail  51  may be disposed inside of the outer column  50  in a predetermined longitudinal direction. Rails  51  of the outer column  50  may be correspondingly formed on each of the upper portion and the lower portion of the fastened inner column  40  such that the outer column  50  may stably move in a vertical direction. 
     The rails  41 ,  51  included in the outer column  50  and the inner column  40  may be correspondingly engaged to each other. The convex rail  41  may be disposed on the outer surface of the inner column  40  and the concave rail  51  may be disposed inside of the outer column  50  such that the inner column  40  is inserted. In addition, a vertical screw  72  fastened to the outer column  50  to allow the outer column  50  to ascend and descend may ascend and descend by a nut  42  disposed in the outer column  50 . 
     Here, a lubricating oil receiver  60  may be disposed to cover an outer surface of the nut  42 . 
     The lubricating oil receiver  60  may be disposed to cover an upper end portion, the outer surface, and a lower end portion of the nut  42  in a longitudinal direction, and the lubricating oil receiver  60  may contain lubricating oil. 
     The lubricating oil receiver  60  may decrease a frictional force between a vertical screw  72  and the nut  42  such that the lubricating oil flows. 
     The lubricating oil receiver  60  may include a lubricating oil container  62  and a lubricating oil cover  61 . A lubricating oil container  62  may be fastened to a lower center of the outer column  50  in a longitudinal direction. 
     The nut  42  may be fastened to the upper end portion of the lubricating oil container  62  and the lubricating oil cover  61  may be disposed on the upper end portion of the nut  42 . At least one hole  63  may be formed inside of the nut  42  in a longitudinal direction such that the lubricating oil flows vertically. For example, two holes may be formed one on each side of the nut  42 . 
     The hole  63  may allow the lubricating oil to flow through the hole  63  by a pressure caused when the vertical screw  72  descends. 
     The lubricating oil container  62  and the lubricating oil cover  61  may be completely sealed such that the lubricating oil is protected from leaking out. When the vertical screw  72  descends, the lubricating oil may flow to the lubricating oil cover  61  by the hole  63 . When the vertical screw  72  ascends, the lubricating oil may flow to an inside where the lubricating oil container  62  is disposed. 
     All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, back, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. The exemplary drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto may vary. 
     Although a few embodiments of the present invention are shown and described, the present invention is not limited to the described embodiments. Rather, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Summary:
A height adjustment device for a rotunda can comprise: an outer column which fixes a rotunda and ascends and descends; an inner column which is connected to the outer column; a vertical screw which is placed on the lower end of the rotunda; a nut which is interlocked in correspondence to the outside diameter of the vertical screw; and rails which are provided on one side of the outer column or the inner column and are formed in correspondence to each other so as to assist the ascent and descent of the outer column.