Abstract:
Disclosed herein is a height adjustment apparatus which is constructed such that the height of an upper board placed thereon is easily adjusted only by lifting the upper board. To achieve the above-mentioned purpose, the height adjustment apparatus includes an actuating unit which controls the height of the apparatus, and a frame unit which is coupled to the actuating unit and is adjusted in height by contraction or extension.

Description:
CROSS REFERENCES 
       [0001]    Applicant claims priority of International Application No. PCT/KR2009/006500 filed Nov. 6, 2009, which claims foreign priority of Korean Patent Application No. 10-2008-0115172, filed Nov. 19, 2008, and Korean Patent Application No. 10-2009-0101630, filed Oct. 26, 2009, with the Korean Intellectual Property Office, where the entire contents are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to height adjustment apparatuses and, more particularly, to a height adjustment apparatus which is constructed such that the height of an upper board placed thereon is easily adjusted just by lifting the upper board. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, a height adjustment apparatus enables the height of an upper board placed thereon to be adjusted according to a body type of a user such that the user conveniently uses the upper board. 
         [0006]    For instance, a representative example of a conventional height adjustment apparatus was proposed in Korean Patent Registration No. 10-0500162 which is shown in  FIG. 1 . 
         [0007]    As shown in  FIG. 1 , in the conventional height adjustment apparatus, a hinge  38  having a basic structure is connected to two support legs  32  at a junction between the support legs  32 . A separate retaining bar  46  for maintaining the height adjustment apparatus at an adjusted height is coupled to the support legs  32 . 
         [0008]    To adjust the height of the height adjustment apparatus having the above-mentioned structure, a user holds one of the support legs  32  using one of his/her hands, manipulates the retaining bar  46  using the other hand, adjusts the height of the height adjustment apparatus, and then fastens the support legs  32  to each other using the retaining bar  46 . However, as such, the process of adjusting the height of the height adjustment apparatus is very complex and thus inconveniences the user. Furthermore, the process and assembly of the steel structure increase the production cost and rate of defectives. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a height adjustment apparatus which is constructed such that the height thereof is adjusted in multi-steps using a gear teeth engagement structure, and when an upper board reaches the uppermost position, the gear teeth are disengaged from each other, thus enabling the height adjustment apparatus to be contracted such that the upper board is disposed at the lowermost position, thereby enabling a user to easily adjust the upper board without requiring manipulation of a separate height adjustment means. 
         [0010]    Another object of the present invention is to provide a height adjustment apparatus in which second and third brackets are coupled to a first bracket which is disposed therebetween and are elastically supported by second and third support rods which are fastened to the second and third brackets, so that because the second and third elastic rods function as elastic members, a separate coupling means for coupling the brackets is not required, thus simplifying the structure of the height adjustment apparatus, thereby reducing the production cost, and facilitating the maintenance and repair thereof. 
         [0011]    In other words, the second and third support rods are slightly bent inwards based on the positions at which they are fastened to the second and third brackets. Thus, the second and third brackets can be fastened to both ends of the first bracket by the elastic force of the second and third support rods. 
         [0012]    A further object of the present invention is to provide a height adjustment apparatus in which first one-way stoppers are provided in the first bracket, so that when the second and third brackets rotate in a predetermined direction, the first one-way stoppers allow the second and third brackets to rotate around the first bracket which is interposed therebetween, in other words, when the second and third brackets rotate in a predetermined direction within a predetermined range, the gear teeth are disengaged from each other, thus enabling the height adjustment apparatus to be easily contracted. 
         [0013]    In order to accomplish the above object, the present invention provides a height adjustment apparatus, including: an actuating unit controlling a height of the height adjustment apparatus; and a frame unit coupled to the actuating unit, the frame unit being adjusted in height by contraction or extension thereof. 
         [0014]    The actuating unit may include: a first bracket provided at a medial portion of the actuating unit; a second bracket coupled to a first end of the first bracket; and a third bracket coupled to a second end of the first bracket. 
         [0015]    The first bracket may have a cylindrical shape. First coupling parts may be respectively provided on upper and lower portions of the circumferential outer surface of the first bracket. A mounting plate may be provided in the first end of the first bracket. A first gear-teethed part may be provided on the mounting plate. A pair of first protrusions may be provided at diametrically opposite positions on the circumferential outer surface of the first gear-teethed part. The first protrusions extend predetermined lengths outside the first gear-teethed part. 
         [0016]    Furthermore, mounting depressions are formed in a circumferential inner surface of both ends of the first bracket, each mounting depression having a predetermined depth, and first locking members are provided in the mounting depression which is adjacent to the second bracket, the first locking members being disposed at positions perpendicular to the first protrusions based on a center of the first bracket. 
         [0017]    In addition, a first one-way stopper may be provided on the mounting plate. The first one-way stopper may be disposed inside the first gear-teethed part. 
         [0018]    As well, a mounting block may be fastened to the mounting plate of the first bracket. The first one-way stopper may be rotatably coupled to the mounting block by a hinge. An elastic member may be fitted over the hinge. 
         [0019]    Moreover, a support protrusion may be provided on the mounting block so that the hinge is fitted into the support protrusion. A stop protrusion may be provided on the mounting block on one side of the support protrusion. An inclined surface may be formed on a first side of the first one-way stopper. 
         [0020]    The elastic member may comprise a torsion spring. 
         [0021]    The first one-way stopper may comprise three first one-way stoppers spaced apart from each other at regular angular intervals. 
         [0022]    The second bracket may have a cylindrical shape and be inserted into the mounting depression formed in the first end of the first bracket. Second coupling parts may be respectively provided on upper and lower portions of the circumferential outer surface of the second bracket. A mounting surface may be formed inside the second bracket. A second gear-teethed part may be provided on the mounting surface. The second gear-teethed part engages with the first gear-teethed part of the first bracket. A locking depression may be formed in the mounting surface and disposed inside the second gear-teethed part so that the first one-way stopper is removably locked to the locking depression. Second locking members may be provided in the second bracket and disposed outside the second gear-teethed part. The second locking members correspond to the first protrusions of the first bracket. 
         [0023]    Furthermore, second protrusions corresponding to the first locking members of the first bracket may protrude from a second end of the second bracket in an axial direction. 
         [0024]    As well, an inclined surface may be formed in one end of the locking depression. 
         [0025]    The height adjustment apparatus may further include a cover covering a first end of the second bracket which is opposite to the second end thereof in which the mounting surface is provided. 
         [0026]    The third bracket may have a cylindrical shape and be inserted into the mounting depression formed in the second end of the first bracket. Third coupling parts may be provided at diametrically opposite positions on the circumferential outer surface of the third bracket. 
         [0027]    The frame unit may include: a first support rod coupled to the first bracket of the actuating unit; a second support rod coupled to the second bracket of the actuating unit; and a third support rod coupled to the third bracket of the actuating unit. 
         [0028]    The first support rod may be inserted through the first coupling parts provided on the upper and lower portions of the first bracket, such that the first support rod protrudes upwards and downwards from the first bracket. The second support rod may be inserted through the second coupling parts provided on the upper and lower portions of the second bracket, such that the second support rod protrudes upwards and downwards from the second bracket. The third support rod may be inserted through the third coupling parts provided on the upper and lower portions of the third bracket, such that the third support rod protrudes upwards and downwards from the third bracket. 
         [0029]    In addition, a connection member may be coupled to an upper end of the first support rod. The connection member may be fastened to an upper board. A first bottom support may be coupled to a lower end of the first support rod. The first bottom support may be supported on the ground. 
         [0030]    The second and third support rods may be respectively coupled to the second and third brackets. Upper and lower ends of the second and third support rods which protrude from the second and third brackets may be curved inwards such that a distance between the second and third support rods is reduced from the second and third brackets to the upper and lower ends thereof. 
         [0031]    Moreover, a top support may be coupled to the upper ends of the second and third support rods. The top support may support the upper board thereon. A second bottom support may be coupled to the lower ends of the second and third support rods. The second bottom support may be supported on the ground. 
         [0032]    In order to accomplish the above object, the present invention provides a height adjustment apparatus, including: a fourth bracket, having a fourth bracket body, fourth coupling parts provided on the fourth bracket body so that a fourth support bar is inserted through the fourth coupling parts and passes through the fourth bracket body, a third gear-teethed part having an annular shape and provided in the fourth bracket body, a plurality of locking protrusions provided in the fourth bracket body around a periphery of the third gear-teethed part at positions spaced apart from each other at regular angular intervals, each of the locking protrusions having an inclined portion, and a plurality of depressions formed in the fourth bracket body around the periphery of the third gear-teethed part at positions spaced apart from each other at regular angular intervals; a fifth bracket, having a fifth bracket body, fifth coupling parts provided on the fifth bracket body so that a fifth support bar is inserted through the fifth coupling parts and passes through the fifth bracket body, a fourth gear-teethed part having an annular shape and provided in the fifth bracket body, and a plurality of locking protrusions provided in the fifth bracket body around a periphery of the fourth gear-teethed part at positions spaced apart from each other at regular angular intervals, wherein the fourth bracket is coupled to a first end of the fifth bracket such that the third gear-teethed part engages with the fourth gear-teethed part; second one-way stoppers provided in the fifth bracket around the periphery of the fourth gear-teethed part at positions spaced apart from each other at regular angular intervals, each of the second one-way stoppers being constructed such that an upper end thereof is elastically bent only in one direction; and a sixth bracket coupled to a second end of the fifth bracket, the sixth bracket having a sixth bracket body, and sixth coupling parts provided on the sixth bracket body so that a sixth support bar is inserted through the sixth coupling parts and passes through the sixth bracket body. Upper ends of the fourth and sixth support rods and lower ends of the fourth and sixth support rods are respectively fastened to top and bottom supports. 
         [0033]    In order to accomplish the above object, the present invention provides a height adjustment apparatus, including: a fourth bracket, having a fourth bracket body, fourth coupling parts provided on the fourth bracket body so that a fourth support bar is inserted through the fourth coupling parts and passes through the fourth bracket body, a third gear-teethed part having an annular shape and provided in the fourth bracket body, and a plurality of locking protrusions provided in the fourth bracket body around a periphery of the third gear-teethed part at positions spaced apart from each other at regular angular intervals, a fifth bracket, having a fifth bracket body, fifth coupling parts provided on the fifth bracket body so that a fifth support bar is inserted through the fifth coupling parts and passes through the fifth bracket body, a fourth gear-teethed part having an annular shape and provided in the fifth bracket body, and a plurality of locking protrusions provided in the fifth bracket body around a periphery of the fourth gear-teethed part at positions spaced apart from each other at regular angular intervals, each of the locking protrusions having an inclined portion, and a plurality of depressions formed in the fifth bracket body around the periphery of the fourth gear-teethed part at positions spaced apart from each other at regular angular intervals, wherein the fourth bracket is coupled to a first end of the fifth bracket such that the third gear-teethed part engages with the fourth gear-teethed part; second one-way stoppers provided in the fourth bracket around the periphery of the third gear-teethed part at positions spaced apart from each other at regular angular intervals, each of the second one-way stoppers being constructed such that an upper end thereof is elastically bent only in one direction; and a sixth bracket coupled to a second end of the fifth bracket, the sixth bracket having a sixth bracket body, and sixth coupling parts provided on the sixth bracket body so that a sixth support bar is inserted through the sixth coupling parts and passes through the sixth bracket body. Upper ends of the fourth and sixth support rods and lower ends of the fourth and sixth support rods may be respectively fastened to top and bottom supports. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0035]      FIG. 1  is a view showing a conventional height adjustment apparatus; 
           [0036]      FIG. 2  is a perspective view illustrating a height adjustment apparatus, according to a first embodiment of the present invention; 
           [0037]      FIG. 3  is a front view illustrating the height adjustment apparatus according to the first embodiment of the present invention; 
           [0038]      FIG. 4  is a side view illustrating the height adjustment apparatus according to the first embodiment of the present invention; 
           [0039]      FIG. 5  is an exploded perspective view of an actuating unit according to the first embodiment of the present invention; 
           [0040]      FIGS. 6A and 6B  are views showing a first one-way stopper according to the first embodiment of the present invention; 
           [0041]      FIGS. 7A and 7B  are views illustrating the operation of first and second brackets of the height adjustment apparatus according to the first embodiment of the present invention; 
           [0042]      FIGS. 8A and 8B  are views illustrating the operation of the first one-way stopper of the height adjustment apparatus according to the first embodiment of the present invention; 
           [0043]      FIGS. 9A through 9C  are views illustrating the operation of contracting the height adjustment apparatus according to the first embodiment of the present invention; 
           [0044]      FIG. 10  is an exploded perspective view illustrating an actuating unit of a height adjustment apparatus, according to a second embodiment of the present invention; 
           [0045]      FIG. 11  illustrates the second embodiment of the present invention, showing the actuating unit of  FIG. 10  coupled to support rods; 
           [0046]      FIG. 12  illustrates the second embodiment of the present invention, showing a fourth bracket; 
           [0047]      FIG. 13  illustrates the second embodiment of the present invention, showing a fifth bracket; 
           [0048]      FIG. 14  is a detailed view showing a second one-way stopper according to the second embodiment of the present invention; and 
           [0049]      FIG. 15  is a view showing the operation of the height adjustment apparatus according to the second embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0050]    Hereinafter, a height adjustment apparatus according to the present invention will be described in detail with reference to the attached drawings. 
       First Embodiment 
       [0051]      FIG. 2  is a perspective view illustrating a height adjustment apparatus  100 , according to a first embodiment of the present invention.  FIG. 3  is a front view illustrating the height adjustment apparatus  100 .  FIG. 4  is a side view illustrating the height adjustment apparatus  100 .  FIG. 5  is an exploded perspective view of an actuating unit  110  of the height adjustment apparatus  100 .  FIGS. 6A and 6B  are views showing a first one-way stopper  140  of the height adjustment apparatus  100 . 
         [0052]    As shown in  FIGS. 2 through 6 , the height adjustment apparatus  100  according to the first embodiment of the present invention includes the actuating unit  110  which controls the height of the height adjustment apparatus  100 . 
         [0053]    The actuating unit  110  includes a first bracket  111 , a second bracket  210  which is coupled to a first end of the first bracket  111 , and a third bracket  310  which is coupled to a second end of the first bracket  111 . 
         [0054]    The first bracket  111  has a cylindrical shape which is open on both ends thereof. First coupling parts  112  symmetrically protrude outwards from upper and lower portions of the circumferential outer surface of the first bracket  111 . A screw hole  113  into which a locking bolt  113   a  is tightened is formed in each first coupling part  112 . 
         [0055]    Furthermore, a mounting plate  114  is provided in the first end of the first bracket  111 . A first gear-teethed part  116  is provided on the outer surface of the mounting plate  114 . 
         [0056]    Two first protrusions  120  are provided at diametrically opposite positions between the circumferential inner surface of the first bracket  111  and the first gear-teethed part  116 . The two first protrusions  120  protrude outwards from the first bracket  111  in the same direction. 
         [0057]    In addition, mounting depressions  122  having predetermined depths are formed in the circumferential inner surface of both ends of the first bracket  111 . Two first locking members  124  are provided in the mounting depression  122  which is adjacent to the first gear-teethed part  116 . The two first locking members  124  are disposed at positions spaced apart from the first protrusions  120  at angles of 90° based on the center of the first bracket  111 . 
         [0058]    Here, an inclined surface is formed on a first end of each first locking member  124 . A locking stop is formed on a second end of the first locking member  124  which is opposite to the inclined surface formed on the first end thereof. 
         [0059]    In addition, the first one-way stopper  140  is provided on the mounting plate  114  and disposed inside the first gear-teethed part  116 . 
         [0060]    To provide the first one-way stopper  140  on the mounting plate  114 , a mounting block  118  is mounted to the mounting plate  114 . Two support protrusions  118   b  protrude upwards from opposite sides of the upper surface (when seen in  FIG. 6 ) of the mounting block  118 . A hinge  118   c  is inserted into the two support protrusions  118   b . A stop protrusion  118   a  is provided on the mounting block  118  at one side of the support protrusions  118   b.    
         [0061]    The first one-way stopper  140  is inserted between the support protrusions  118   b  and coupled to the mounting block  118  by the hinge  118   c . An inclined surface  142  is formed on a first end of the first one-way stopper  140  at a side corresponding to the stop protrusion  118   a  provided on the mounting block  118 . An insert depression  114  is formed in the first one-way stopper  140  at a position opposite the inclined surface  142 . An elastic member  146  is provided around the hinge  118   c  and disposed in the insert depression  144 . A first end of the elastic member  146  extends outwards from the first one-way stopper  140  and is supported at a first end thereof on the surface of the mounting plate  114 . Thereby, the elastic member  146  elastically supports the first one-way stopper  140 . 
         [0062]    Preferably, a torsion spring is used as the elastic member  146  which elastically supports the first one-way stopper  140 . 
         [0063]    In the embodiment, three first one-way stoppers  140  are provided on the mounting plate  114  at positions spaced apart from each other at regular angular intervals in the circumferential direction. 
         [0064]    Meanwhile, the second bracket  210  is fitted into the mounting depression  122  of the first bracket  111  which is adjacent to the mounting plate  114 . 
         [0065]    In detail, the second bracket  210  has a cylindrical shape. Two second coupling parts  212  protrude outwards from the upper and lower portions of the circumferential outer surface of the second bracket  210 . A screw hole  213  into which a locking bolt  213   a  is tightened is formed in each second coupling part  212 . 
         [0066]    Furthermore, a mounting surface  214  corresponding to the mounting plate  114  of the first bracket  111  is formed inside the second bracket  210 . A second gear-teethed part  216  which engages with the first gear-teethed part  116  of the first bracket  111  is formed on the mounting surface  214 . In addition, locking depressions  218  are formed in the mounting surface  214  and disposed inside the second gear-teethed part  216 . The first one-way stoppers  140  are removably locked to the corresponding locking depressions  218 . 
         [0067]    Here, an inclined surface  218   a  is formed in each locking depression  218  at a position corresponding to the inclined surface  142  of the first one-way stopper  140 . A stop surface  218   b  is formed in the locking depression  218  at a position opposite to the inclined surface  218   a.    
         [0068]    Furthermore, second locking members  220  corresponding to the first protrusions  120  of the first bracket  111  are provided outside the second gear-teethed part  216 . 
         [0069]    A guide surface  220   a  is formed on each second locking member  220  at a position opposite to the inclined surface  142  of the first one-way stopper  140  with respect to the direction in which the second locking member  220  rotates. 
         [0070]    In addition, second protrusions  224  are provided on the rim of a second end of the second bracket  210  which is inserted into the mounting depression  122  that is formed adjacent to the mounting plate  114  of the first bracket  111 . The second protrusions  224  correspond to the first locking members  124  of the first bracket  111 . 
         [0071]    Here, a guide surface  224   a  is formed on a front surface (first end) of each second protrusion  224  with respect to the direction in which it is advanced when the second bracket  210  rotates. A locking stop  224   b  is formed on the second protrusion  224  at a position opposite to the guide surface  224   a.    
         [0072]    In the embodiment, a cover  240  covers a first end of the second bracket  210  which is opposite to the second end thereof which is coupled to the first bracket  111 . 
         [0073]    The third bracket  310  is coupled to the second end of the first bracket  111  which is opposite to the second bracket  210 . 
         [0074]    The third bracket  310  has a cylindrical shape and is fitted at a first end thereof into the mounting depression  122  which is formed in the second end of the first bracket  111  which is opposite to the second bracket  210 . The third bracket  310  is sealed on a second end thereof which is opposite to the first end which is coupled to the first bracket  111 . 
         [0075]    Furthermore, two third coupling parts  312  protrude outwards from the circumferential outer surface of the third bracket  310  at positions corresponding to the second coupling parts  212  of the second bracket  210 . 
         [0076]    A screw hole  313  is formed in each third coupling part  312 . A locking bolt  313   a  is tightened into the screw hole  313 . 
         [0077]    In addition, in the present invention, a frame unit  410  is coupled to the actuating unit  100  so that the height thereof is adjusted in height by contracting or extending it. 
         [0078]    The frame unit  410  includes a first support rod  411  which is coupled to the first bracket  111 , a second support rod  420  which is coupled to the second bracket  210 , and a third support rod  430  which is coupled to the third bracket  310 . 
         [0079]    In detail, the first support rod  411  is inserted into the first coupling parts  112  of the first bracket  111  such that the first support rod  411  passes through the first coupling parts  112  and protrudes upwards and downwards from the first bracket  111 . The first support rod  411  which is inserted into the first coupling parts  112  are fastened to the first bracket  111  by the locking bolts  113   a  which are tightened into the screw holes  113  formed in the first coupling parts  112 . 
         [0080]    Here, an upper part of the first support rod  411  which protrudes upwards from the first bracket  111  is coupled to a connection member  413  which is fastened to the lower surface of an upper board  102 . A lower par of the first support rod  411  which protrudes downwards from the first bracket  111  is coupled to a first bottom support  415  which is placed on the ground. 
         [0081]    Furthermore, the second support rod  420  is inserted through the second coupling parts  212  of the second bracket  210  and protrudes upwards and downwards from the second bracket  210 , such that the first and second support rods  411  and  420  form an “X”-shaped structure. The second support rod  420  rotates around the actuating unit  110  in the direction in which the first support rod  411  rotates around the actuating unit  110 , while maintaining the “X”-shaped structure. 
         [0082]    The third support rod  430  is coupled to the third coupling part  312  of the third bracket  310  such that the third support rod  430  protrudes upwards and downwards from the third coupling part  312 . The third support rod  430  is oriented in the direction corresponding to the second support rod  420  and rotates in the same direction as that of the second support rod  420 . 
         [0083]    Here, a distance between the upper and lower parts of the second and third support rods  420  and  430  which protrude upwards and downwards from the second and third brackets  210  and  310  is reduced from the second and third brackets  210  and  310  to both ends of the second and third support rods  420  and  430 . In other words, each of the upper and lower parts of the second and third support rods  420  and  430  is slightly bent inwards at an angle of θ such that elastic force is applied to the second and third brackets  210  and  310  towards the first bracket  111 . 
         [0084]    Thus, the second and third brackets  210  and  310  are brought into close contact with the first bracket  111  by the elastic force of the second and third support rods  420  and  430 , so that the second and third brackets  210  and  310  are prevented from becoming removed from the first bracket  111  when the first, second and third brackets  111 ,  210  and  310  are operated. 
         [0085]    Furthermore, a top support  422  is coupled to the upper ends of the second and third support rods  420  and  430  which protrude upwards from the second and third brackets  210  and  310 . The upper board  102  is seated onto the top support  422 . 
         [0086]    In addition, a second bottom support  424  which is placed on the ground is coupled to the lower ends of the second and third support rods  420  and  430  which protrude downwards from the second and third brackets  210  and  310 . 
         [0087]    As such, the coupling of the second and third brackets  210  and  310  to the first bracket  111  can be reliably retained by the elastic pressing force of the second and third support rods  420  and  430 . 
         [0088]    In the embodiment, the first, second and third support rods  411 ,  420  and  430  have been illustrated as being respectively inserted through the first, second and third coupling parts  112 ,  212  and  312  of the first, second and third brackets  111 ,  210  and  310  and being protruded upwards and downwards from the first, second and third brackets  111 ,  210  and  310 . However, alternatively, each of the first, second and third support rods  411 ,  420  and  430  may have a structure such that it is divided into upper and lower parts. In this case, the divided upper and lower parts of the first, second and third support rods  411 ,  420  and  430  are respectively and independently coupled to the first, second and third coupling parts  112 ,  212  and  312  which are provided on the upper and lower portions of the first, second and third brackets  111 ,  210  and  310 . 
         [0089]    The operation of the height adjustment apparatus  100  according to the first embodiment of the present invention having the above-mentioned construction will be explained below. 
         [0090]      FIGS. 7A and 7B  are views illustrating the operation of first and second brackets  111  and  210  of the height adjustment apparatus  100  according to the first embodiment of the present invention.  FIGS. 8A and 8B  are views illustrating the operation of the first one-way stopper  140  of the height adjustment apparatus  100 .  FIGS. 9A through 9C  are views illustrating the operation of contracting the height adjustment apparatus  100 . 
         [0091]    As shown in these drawings, in the height adjustment apparatus  100 , the first gear-teethed part  116  of the first bracket  111  engages with the second gear-teethed part  216  of the second bracket  210 . Each first protrusion  120  of the first bracket  111  is maintained in the state of being in close contact with a second end of the corresponding second locking member  220  of the second bracket  210  which is opposite to the guide surface  220   a  formed on the first end of the second locking member  220 . Each first locking member  124  of the first bracket  111  is in the state of being in close contact with a second end of the second protrusion  224  of the second bracket  210  which is opposite to the guide surface  224   a  formed on the first end of the second protrusion  224 . 
         [0092]    Furthermore, the first one-way stoppers  140  of the first bracket  111  are maintained in the state of being inserted in the corresponding locking depressions  218  formed in the mounting surface  214  of the second bracket  210 . 
         [0093]    In this state, when a user wants to adjust the height of the upper board  102 , the user holds the upper board  102  and lifts it upwards. Then, the second and third brackets  210  and  310  rotate with respect to the first bracket  111 , and the height adjustment apparatus  100  which has been in the contracted state is extended. 
         [0094]    That is, the first gear-teethed part  116  of the first bracket  111  and the second gear-teethed part  216  of the second bracket  210  pass over the inclined surfaces of the gear teeth of each other and move relative to each other, thus allowing the height adjustment apparatus  100  to be extended. Here, because the inclined surface is formed on only one side of each gear tooth of the first and second gear-teethed parts  116  and  216 , each of the first and second brackets  111  and  210  can rotate only in one direction and cannot rotate in the reverse direction. 
         [0095]    Here, when the first gear-teethed part  116  of the first bracket  111  and the second gear-teethed part  216  of the second bracket  210  pass over the inclined surfaces of the gear teeth of each other, the first bracket  111  and the second bracket  210  move away from each other. However, because the second and third support rods  420  and  430  elastically push the second and third brackets  210  and  310  towards the first bracket  111 , the second and third brackets  210  and  310  move away from the first bracket  111  only by the distance equal to the height of the inclined surfaces of the first and second gear-teethed parts  116  and  216 , rather than being completely removed from the first bracket  111 . The second and third brackets  210  and  310  which have slightly moved away from the first bracket  111  are returned to their original states by the elastic force of the second and third support rods  420  and  430 . 
         [0096]    Furthermore, when the second and third brackets  210  and  310  rotate with respect to the first bracket  111 , the first one-way stoppers  140  of the first bracket  111  are moved along the inclined surfaces  218   a  of the corresponding locking depressions  218  of the second bracket  210  and removed from the locking depressions  218 . At this time, each first one-way stopper  140  compresses the elastic member  146  and rotates around the hinge  118   c  in the direction opposite to the direction in which the first bracket  111  rotates with respect to the second bracket  210 . Thereafter, the first one-way stoppers  140  come into close contact with the mounting surface  214  of the second bracket  210 . In this state, the second bracket  210  rotates with respect to the first bracket  111 . 
         [0097]    As such, when the upper board  102  is lifted, the first bracket  111  is rotated by the first support rod  411  which is coupled to the connection member  413  fastened to the lower surface of the upper board  102 . Simultaneously, the second and third brackets  210  and  310  rotate with respect to the first bracket  111 . The user can adjust the height of the upper board  102  to a desired degree. 
         [0098]    Furthermore, when the user who has held the upper board  102  and lifted it to a desired height releases the upper board, the first gear-teethed part  116  of the first bracket  111  is locked to the second gear-teethed part  216  of the second bracket  210  at that position, so that the upper board  102  is retained at the adjusted height. 
         [0099]    Conversely, when it is desired to contract the height adjustment apparatus  100 , the user holds the upper board  102  and lifts it to the uppermost position. Then, the first protrusions  120  of the first bracket  111  move onto the corresponding second locking members  220  along the guide surfaces  220   a  of the second locking members  220  and engage with the upper portions of the second locking members  220 . Simultaneously, the first locking members  124  of the first bracket  111  move onto the corresponding second protrusions  224  of the second bracket  210  along the guide surfaces  224   a  of the second protrusions  224  and engage with the upper portions of the second protrusions  224 . 
         [0100]    As such, because the first protrusions  120  are disposed at the upper portions of the corresponding second locking members  220  and the first locking members  124  are disposed at the upper portions of the corresponding second protrusions  224 , the second bracket  210  moves away from the first bracket  111  by a predetermined distance. Hereby, the first gear-teethed part  116  is disengaged from the second gear-teethed part  216 . In addition, when the second bracket  210  moves away from the first bracket  111  by a predetermined distance, the first one-way stoppers  140  are rotated around the hinge  118   c  by the elastic force of the elastic members  146  and seated onto the stop protrusion  118   a  of the mounting block  118 . Thereafter, the first one-way stoppers  140  are maintained in the upright state. 
         [0101]    In addition, the mounting surface  214  of the second bracket  210  is supported on the upper ends of the first one-way stoppers  140  which are in the upright state. In this state, when the user moves the upper board  102  downwards, the second and third brackets  210  and  310  rotate with respect to the first bracket  111  in the direction opposite to the direction in which they rotate around the first bracket  111  when the upper board  102  moves upwards. Thus, the height adjustment apparatus  100  is contracted. 
         [0102]    When the second and third brackets  210  and  310  which have rotated around the first bracket  111  are returned to their original positions, the first one-way stoppers  140  are inserted into the corresponding locking depressions  218  to which the first one-way stoppers  140  had been locked at first. Thereafter, the first one-way stoppers  140  are supported by the stop surfaces  218   b  of the locking depressions  218 . Simultaneously, the first and second gear-teethed parts  116  and  216  engage with each other, so that the height adjustment apparatus  100  retains the contracted state. 
         [0103]    Furthermore, the rear ends of the first protrusions  120  of the first bracket  111  are stopped by the corresponding second locking members  220  of the second bracket  210 , and the rear ends of the first locking members  124  of the first bracket  111  are stopped by the second protrusions  224  of the second bracket  210 , such that the second and third brackets  210  and  310  can no longer rotate with respect to the first bracket  111 . 
         [0104]    In this state, when the user lifts the upper board  102  upwards, the first one-way stoppers  140  are removed from the locking depressions  218 , and each first one-way stopper  140  rotates around the hinge  118   c  and comes into close contact with the mounting surface  214 . The first and second gear-teethed parts  116  and  216  of the first and second brackets  111  and  210  pass over the gear teeth of each other and move relative to each other without the first and second brackets  111  and  210  being completely spaced apart from each other. 
         [0105]    That is, while the height of the upper board  120  is adjusted, the first protrusions  120  and the first locking members  124  of the first bracket  111  reciprocate between the second locking members  220  and the second protrusions  224  of the second bracket  210 . When the height adjustment apparatus  100  is extended to lift the upper board  120 , the first one-way stoppers  140  move after they rotate downwards around the hinges  118   c , so that the first and second gear-teethed parts  116  and  216  are prevented from being completely disengaged from each other. When each first one-way stopper  140  moves in the reverse direction, it is rotated around the hinge  118   c  and returned to its original state, that is, to the upright state. In this state, the first and second brackets  111  and  210  are maintained in the state of being moved away from each other. Hence, the first and second gear-teethed parts  116  and  216  are also maintained in the state of being disengaged from each other, thus enabling the height adjustment apparatus  100  to be contracted. 
         [0106]    Therefore, when the user holds the upper board  102  and lifts it, the height adjustment apparatus  100  is extended by a degree with which the user lifts the upper boards  102 . When the upper board  102  is lifted to the uppermost position, the first and second gear-teethed parts  116  and  216  are disengaged from each other, thus allowing the height adjustment apparatus  100  to be contracted, so that the upper board  102  can move downwards by its own weight. 
         [0107]    Meanwhile, unlike the first embodiment, the construction provided for the first bracket  111  may be formed in one of the second and third brackets  210  and  310 . In this case, the construction of the second bracket  210  of the first embodiment is provided in the first bracket  111 . 
       Second Embodiment 
       [0108]      FIG. 10  is an exploded perspective view illustrating an actuating unit of a height adjustment apparatus, according to a second embodiment of the present invention. The height adjustment apparatus of the second embodiment includes a fourth bracket  1100 , a fifth bracket  1300  and a sixth bracket  1400 . Fourth coupling parts  1110  and  1120  are provided on the circumferential outer surface of the fourth bracket  1100  at diametrically opposite positions. As shown in  FIG. 11 , a fourth support rod  1500  which passes through the body of the fourth bracket  1100  is inserted through the fourth coupling parts  1110  and  1120 . A third gear-teethed part  1130  having an annular shape is provided in the fourth bracket  1100  at a side facing the fifth bracket  1300 . 
         [0109]    Furthermore, as shown in  FIG. 12 , in the fourth bracket  1100 , locking release parts  1140  are formed outside the third gear-teethed part  1130  along the periphery of the third gear-teethed part  1130  at positions spaced apart from each other at regular angular intervals. Each locking release part  1140  includes a locking protrusion  1141  and a depression  1145 . 
         [0110]    The locking protrusion  1141  includes an inclined portion  1142  which is contiguous at a first end thereof with the bottom, and a planar portion  1143  which extends from a second end of the inclined portion  1142 . The locking protrusion  1141  further includes a stopper  1144  which is provided on the end of the planar portion  1143  that is opposite to the inclined portion  1142 . 
         [0111]    In addition, inclined surfaces  1146  and  1147  are formed at both sides in the depression  1145  such that both ends of the depression  1145  are contiguous with the bottom on which the locking protrusion  1141  is provided. 
         [0112]    Meanwhile, fifth coupling parts  1310  and  1320  are provided on the circumferential outer surface of the fifth bracket  1300  at diametrically opposite positions. A fifth support rod  1600  is inserted through the fifth coupling parts  1310  and  1320  and passes through the body of the fifth bracket  1300  such that the fifth support rod  1600  crosses over the fourth support rod  1500 . 
         [0113]    Furthermore, a fourth gear-teethed part  1330  having an annular shape is provided in the fifth bracket  1300  at a side facing the fourth bracket  1100 . The fourth gear-teethed part  1330  engages with the third gear-teethed part  1130  of the fourth bracket  1100 . 
         [0114]    As shown in  FIG. 13 , in the fifth bracket  1300 , locking protrusions  1340  are provided outside the fourth gear-teethed part  1330  along the periphery of the fourth gear-teethed part  1330  at positions spaced apart from each other at regular angular intervals. The locking protrusions  1340  of the same number as the locking release parts  1140  are disposed at positions corresponding to the locking release parts  1140 . 
         [0115]    As shown in  FIG. 14A , a second one-way stopper  1200  is disposed adjacent to each locking protrusion  1340 . The second one-way stopper  1200  is constructed such that the upper end thereof elastically rotates only in one direction around a mounting block  1210  which is fastened to the fifth bracket  1300 . 
         [0116]    Furthermore, a spring is provided between a rotating member  1220  and the mounting block  1210 , such that restoring force is applied to the second one-way stopper  1220 , as shown in  FIG. 14   b.    
         [0117]    Meanwhile, sixth coupling parts  1410  and  1420  are provided on the circumferential outer surface of the sixth bracket  1400  at diametrically opposite positions. A sixth support rod  1700  is inserted through the sixth coupling parts  1410  and  1420  and passes through the body of the sixth bracket  1400  such that the sixth support rod  1700  is parallel with the fourth support rod  1500 . 
         [0118]    The upper ends of the fourth and sixth support rods  1500  and  1700  are fastened to a top support (not shown) such that a distance therebetween is maintained constant. The lower ends of the fourth and sixth support rods  1500  and  1700  are fastened to a bottom support  1800  such that a distance therebetween is maintained constant. 
         [0119]    Therefore, as shown in  FIG. 11 , the fourth bracket  1100 , the fifth bracket  1300  and the sixth brackets  1400  are coupled to each other by the fourth support rod  1500  and the sixth support rod  1700 . 
         [0120]    The operation of the height adjustment apparatus according to the second embodiment of the present invention having the above-mentioned construction will be explained below. 
         [0121]      FIG. 15  illustrates the operation of the height adjustment apparatus according to the second embodiment. As shown in the drawing, an upper board  1102  is placed on the upper end of the height adjustment apparatus. The upper end of the fifth support rod  1600  is fastened to the lower surface of the upper board  1102 . 
         [0122]    As shown in  FIG. 15D , the height adjustment apparatus is in the contracted state at first. In this case, the third gear-teethed part  1130  of the fourth bracket  1100  engages with the fourth gear-teethed part  1330  of the fifth bracket  1300 . Furthermore, the locking protrusions  1340  of the fifth bracket  1300  are in the state of being in contact with the bottom of the fourth bracket  1100  behind the rear ends of the corresponding locking protrusions  1141 . 
         [0123]    When the user lifts the upper board  1102  to adjust the height thereof, the height adjustment apparatus is extended by its own weight. Here, the third gear-teethed part  1130  of the fourth bracket  1100  and the fourth gear-teethed part  1330  of the fifth bracket  1300  pass over the inclined surfaces of the gear teeth of each other and move relative to each other, thus allowing the height adjustment apparatus to be extended. 
         [0124]    When the third gear-teethed part  1130  of the fourth bracket  1100  and the fourth gear-teethed part  1330  of the fifth bracket  1300  pass over the inclined surfaces of each other, the fourth bracket  1100  and the fifth bracket  1300  slightly move away from each other, but they are not completely separated from each other because the fourth support rod  1500  and the sixth support  1700  elastically support the fourth bracket  1100  and the fifth bracket  1300 . 
         [0125]    If the user stops to lift the upper board  1102  when it reaches a desired height, the third gear-teethed part  1130  of the fourth bracket  1100  is locked to the fourth gear-teethed part  1330  of the fifth bracket  1300 , so that the upper board  1102  is retained at the adjusted height, as shown in  FIG. 15B  or  15 C. 
         [0126]    Here, when the height adjustment apparatus is in the contracted state, the rotating members  1220  of the second one-way stoppers  1200  are in contact with the bottom surface of the fourth bracket  1100  and are in the state of having rotated (bent) downwards. When the height adjustment apparatus is extended from this state, the second one-way stoppers  1200  rotate along with the fifth bracket  1300  while the rotating members  1220  maintain the above-mentioned state. Meanwhile, to contract the height adjustment apparatus which has been extended, the user lifts the upper board  1102  to the uppermost position, as shown in  FIG. 15A . Then, the fifth bracket  1300  further rotates with respect to the fourth bracket  1100 , so that the locking protrusions  1340  of the fifth bracket  1300  move onto the inclined portions  1142  and the planar portions  1143  of the corresponding locking protrusions  1141  of the fourth bracket  1100  and then are stopped to the stoppers  1144  of the locking protrusions  1141 . 
         [0127]    Thus, due to the height of the locking protrusions  1340  and  1141 , the third gear-teethed part  1130  of the fourth bracket  1100  is completely removed from the fourth gear-teethed part  1330  of the fifth bracket  1300 . Simultaneously, the second one-way stoppers  1200  move along the corresponding inclined surfaces  1146  and are inserted into the depressions  1145 . Hereby, as shown in  FIG. 14B , the rotating members  1220  of the second one-way stoppers  1200  rotate upwards, thus maintaining the state in which the fourth and fifth brackets  1100  and  1300  move away from each other. 
         [0128]    In this state, that is, when the fourth and fifth brackets  1100  and  1300  are in the state of being completely spaced apart from each other, if the user releases the upper board  1102 , the height adjustment apparatus is contracted by its own weight and the weight of the upper board  1102 , as shown in  FIG. 15D . In this process, the fifth bracket  1300  reversely rotates and the second one-way stoppers  1200  move along the inclined surfaces  1146  and are removed from the depressions  1143 . Thereafter, the second one-way stoppers  1200  rotate along with the fifth bracket  1300  and are inserted into the depressions  1141  of the neighboring locking release parts  1140  via the corresponding inclined surfaces  1147  of the depressions  1141 . 
         [0129]    Therefore, the third gear-teethed part  1130  of the fourth bracket  1100  engages with the fourth gear-teethed part  1330  of the fifth bracket  1300  again. 
         [0130]    Furthermore, the locking protrusions  1340  are locked to the rear ends of the stoppers  1144  of the locking protrusions  1141  of the neighboring locking release part  1140 . When the user lifts the upper board  1102  again, the second one-way stoppers  1200  are moved along the corresponding inclined surfaces  1147  and removed from the depressions  1145 , and the rotating members  1220  of the second one-way stoppers  1200  are rotated downwards again. The fourth bracket  1100  and the fifth bracket  1300  rotate with respect to each other in the state in which they are not completely spaced apart from each other. Thus, the third gear-teethed part  1130  of the fourth bracket  1100  and the fourth gear-teethed part  1330  of the fifth bracket  1300  pass over the inclined surfaces of the gear teeth of each other and move relative to each other while maintaining the engaged state. 
         [0131]    As such, when the height of the height adjustment apparatus is adjusted, the locking protrusions  1340  of the fifth bracket  1300  reciprocate between the adjacent locking release parts  1140  of the fourth bracket  1100 . Here, when the height adjustment apparatus is extended, the second one-way stoppers  1200  move in the state of having rotated downwards so as to prevent the three and fourth gear-teethed parts  1130  and  1330  from being disengaged from each other. When the second one-way stoppers  1200  move in the reverse direction, the rotating members  1220  rotate upwards, thus moving the fourth bracket  1100  away from the fifth bracket  1300 , thereby enabling the height adjustment apparatus to be contracted. 
         [0132]    In other words, the height adjustment apparatus of the present invention is extended by a degree with which the user applies force to the upper board  1102  upwards, and then it is retained at that height. When the upper board  1102  is lifted to the uppermost height, the three and fourth gear-teethed parts  1130  and  1330  are disengaged from each other, thus allowing the height adjustment apparatus to be contracted by its own weight. 
         [0133]    Meanwhile, the height adjustment apparatus of the second embodiment may be constructed such that the positions of the fourth bracket  1100  and the fifth bracket  1300  are switched. That is, the fifth bracket  1300  having the second on-way stoppers  1200  may be disposed at the position of the fourth bracket  1100 , and the fourth bracket  1100  may be disposed at the position of the fifth bracket  1300 . 
         [0134]    In this case, the sixth bracket  1400  is coupled to the rear side of the fourth bracket  1100  that is changed in position. The operation of this modified construction is the same as that of the second embodiment which was stated above. 
         [0135]    In the embodiments, although the height adjustment apparatus according to the present invention has been illustrated as being used for an ironing board, the present invention is not limited to this. The present invention can be modified in various manners without departing from the scope and spirit of the invention as disclosed in the accompanying claims, for example, it may be used for a table, a desk, and so on. These modifications must be regarded as falling within the bounds of the present invention. 
         [0136]    As described above, a height adjustment apparatus according to the present invention is constructed such that the height thereof is adjusted in multi-steps using a gear teeth engagement structure. Furthermore, when an upper board reaches the uppermost position, the gear teeth are disengaged from each other, thus enabling the height adjustment apparatus to be contracted such that the upper board is disposed at the lowermost position. Therefore, a user can easily adjust the upper board only through a single process. 
         [0137]    Furthermore, second and third brackets are coupled to a first bracket which is disposed therebetween and are elastically supported by second and third support rods which are fastened to the second and third brackets. Thus, because the second and third elastic rods function as elastic members, a separate coupling means for coupling the brackets is not required. Therefore, the structure of the height adjustment apparatus is simplified, thereby reducing the production cost, and facilitating maintenance and repair. 
         [0138]    In other words, the second and third support rods are slightly bent inwards based on the positions at which they are fastened to the second and third brackets. Thus, the second and third brackets are fastened to both ends of the first bracket by the elastic force of the second and third support rods. 
         [0139]    As well, first one-way stoppers are provided in the first bracket. When the second and third brackets rotate in a predetermined direction, the first one-way stoppers allow the second and third brackets to freely rotate around the first bracket which is interposed therebetween. That is, when the second and third brackets rotate in a predetermined direction within a predetermined range, the gear teeth are disengaged from each other, thus enabling the height adjustment apparatus to be easily contracted.