You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a folding electric device, and more particularly, to a folding electric device having perpendicular and horizontal shafts. 
     2. Description of the Related Art 
     Conventional structures for electric devices, especially mobile phones, include a straight type and a folding type. Among these, the folding type mobile phone is more widely preferred because it can be stored in a compact manner. Therefore, the demand for this type of structure it is increasing. 
       FIG. 1  describes one such conventional folding mobile phone  1 .  FIG. 1  is a perspective view of a conventional mobile phone. 
     In  FIG. 1 , a folding mobile phone has substantially semi-elliptic lower and upper units  700  and  711 . Lower unit  700  has operating section  702  and upper unit  711  has rectangular display  712 . Joint member  720  connects units  700  and  711  with each other so that an operating section face  701  and a display attachment face  710  are opposed to each other when the phone is folded. Upper unit  711  is capable of being opened and closed with respect to lower unit  700 . 
     Mobile phones are now used as a personal digital assistants having not only a telecommunication function but also a browser function such as Internet, transmission and reception of e-mail, schedule control, etc. Therefore, display contents are more varied and include character information, pictures, graphics, etc. As a result, the size of the display section has increased. 
     In the conventional folding mobile phone, when the user looks at a display section or performs any operation, it is necessary to position the upper and lower units in an open state. Because the upper and lower units must be opened and closed frequently, it is not very convenient for the user. Therefore, there is room for improving the conventional folding mobile phone in order to make it easier to use. 
     Also in the conventional folding mobile phone, since the display contents are displayed to match a perpendicularity-oriented screen, when displayed characters are read, the number of characters on each line is small. As a result, the user may have difficulty in reading the display contents. 
     Also, when wide images are displayed, the image must be reduced in size, or the user must scroll back and forth to view the entire image. This is another usability problem with the conventional folding mobile phone. 
     Furthermore, since the joint member  720  as shown in  FIG. 1  must be secured, design options are limited. 
     In addition to the mobile phone, other folding equipment, such as personal digital assistants (PDAs), in which a display and an operating section are arranged separately in two units connected to each other so as to be capable of being opened and closed in the same manner as described above, generally have the same problems. 
     Another conventional folding mobile phone is disclosed in the Japanese Patent Application Publication Laid-Open Kokai No. H11-30226.  FIGS. 2(   a )- 2 ( c ) are perspective views of the folding mobile phone described in that Publication. 
     In  FIGS. 2(   a )- 2 ( c ), the folding mobile phone has lower and upper units  804  and  802 , respectively. Lower unit  804  has operating section  803  and upper unit  802  has display  801 . Pivot  806  is provided at right angles on journal  805   a  of hinge  805  connecting upper unit  802  to lower unit  804 . Upper unit  802  can be opened and closed as shown by arrow A′ with hinge  805 . Upper unit  802 , furthermore, can be turned as shown by arrow B′ with pivot  806  so that display  801  is exposed even if the folding mobile phone is folded. 
     This Publication also discloses a configuration in which a rotation restricting mechanism for restricting rotation at a reversing position and a click locking mechanism for holding the rotation restricted state are provided in pivot  806 . 
     Still another conventional folding mobile phone is disclosed in the Japanese Patent Application Publication Laid-Open Kokai No. H11-215218.  FIG. 3(   a ) is a perspective view and  FIGS. 3(   b )- 3 ( c ) are plane views of the folding mobile phone described in that Publication. 
     In  FIGS. 3(   a )- 3 ( c ), mobile phone  910  is configured so that upper unit  906  provided with a display  907  can be turned over and closed as shown by the arrow with hinge  905 . Hinge  905  is formed by a ball joint. Hinge  905  connects upper unit  906  to lower unit  901  so that the phone can be opened and closed, and supports upper unit  906  so that upper unit  906  can turn relative to lower unit  901  in an opened state. 
     Moreover, the Japanese Patent Application Publication Laid-Open Kokai No. 2002-158758 discloses still another convention folding mobile phone. The Publication shows a mobile phone wherein the user can look at a display or can perform simple operations when the upper and lower units are not opened. 
     The Japanese Patent Application Publication Laid-Open Kokai No. 2001-156893 shows a mobile phone that switches the display from a perpendicular orientation to a horizontal orientation, or vice versa, along with the rotation of the display unit. 
     The Japanese Patent Application Publication Laid-Open Kokai No. 5-211547 shows a mobile phone wherein a lower unit is pivotally supported on a upper unit and joint face of the units are formed into a curve. Thus a receiver and a transmitter have a distance and an angle suitable for communication. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an improved structure of a folding electric device. 
     In order to achieve the forgoing object, a folding electric device according to the present invention includes: an upper unit; a lower unit; and a hinge that connects said upper unit to the lower unit. The hinge includes: (a) a perpendicular opening and closing shaft to open and close the upper unit with respect to the lower unit; and (b) a horizontal rotation shaft, fixed vertically on the surface of the lower unit, to rotate the upper unit with respect to the lower unit coming in contact with each other. The present invention may further include a winding flexible board, wound around one of the ends of the perpendicular opening and closing shaft, for electrically connecting the upper unit to the lower unit. Also, the present invention may further include an winding flexible board, wound around the horizontal rotation shaft, for electrically connecting the upper unit to the lower unit. Moreover, the present invention may include an operation input section, mounted on the hinge and electrically connected to the winding flexible board so that a user can operate the operation input section when the folding electric device is in a folded state. In the present invention, the folding electric device may be a folding mobile phone. 
     The present invention may further include a display arranged on the upper unit. Still furthermore, the present invention may include input keys arranged on the lower unit. 
     Another embodiment of a folding electric device according to the present invention includes: an upper unit; a lower unit; and a hinge that connects the upper unit to the lower unit. The hinge includes: (a) a perpendicular opening and closed shaft to open and close the upper unit with respect to the lower unit; (b) a horizontal rotation shaft to rotate the upper unit with respect to the lower unit; (c) brackets fixed at the right and left of the horizontal rotation shift in a direction perpendicular to the horizontal rotation shaft and connected to the perpendicular opening and closed shaft in the opening and closing shaft direction of said bracket; (d) a base, on which the horizontal rotation shaft is mounted, fixed to the lower unit; and (e) a mount provided between the brackets. The present invention may further include a winding flexible board, wound around one of the ends of said perpendicular opening, for electrically connecting the upper unit to lower unit. The present invention may further include a bobbin, arranged between the horizontal rotation shaft and the base, for winding the winding flexible board around the horizontal rotation shaft. Moreover, the present invention may further include a flexible board fixing member for fixing the flexible board. Still furthermore, the present invention may include an operation input section, mounted on the mount, for electrically connecting to the winding flexible board so that a user can operate the operation input section when the folding electric device is in a folded state. In the present invention, the folding electric device may be a folding mobile phone. The present invention may further include a display arranged on the upper unit. Also, the present invention may further include input keys arranged on the lower unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of the invention will be become fully apparent from the following detailed description taken in conjunction with accompanying drawings. 
         FIG. 1  is a perspective view of a conventional mobile phone. 
         FIGS. 2(   a )- 2 ( c ) are perspective views of another conventional folding mobile phone. 
         FIG. 3(   a ) is a perspective view and  FIGS. 3(   b )- 3 ( c ) are plane views of another conventional folding mobile phone. 
         FIG. 4  is a perspective view of a preferred embodiment of a folding mobile phone when a phone is in an open state according to the present invention. 
         FIG. 5  is a perspective view of a preferred embodiment showing rotation of an upper unit with respect to a lower unit in a folding mobile phone according to the present invention. 
         FIG. 6  is a perspective view of a preferred embodiment of a folding mobile phone when the phone is in a folded state according to the present invention. 
         FIG. 7  is a perspective view of a preferred embodiment showing the detailed interior structure of a hinge of a folding mobile phone according to the present invention. 
         FIG. 8  is an exploded perspective view of a preferred embodiment showing the relationship between a hinge and a front cover and a back cover of an upper unit in a folding mobile phone according to the present invention. 
         FIG. 9  is an enlarged perspective view of a preferred embodiment showing a bracket of a folding mobile phone according to the present invention. 
         FIG. 10  is a perspective view of a preferred embodiment showing a state in which a perpendicular open and closed shaft and a bracket are connected to each other in a folding mobile phone according to the present invention. 
         FIG. 11  is a perspective view of a preferred embodiment showing a state in which a front cover and a back cover are engaged with each other in a folding mobile phone according to the present invention. 
         FIG. 12  ( a ) is an exploded view showing a construction of a perpendicular open and closing shaft and  FIG. 12  ( b ) is a sectional view of a front cover engagement portion in a folding mobile phone according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 4  shows a perspective view of a preferred embodiment of a folding mobile phone when a phone is in an open state according to the present invention. 
     Referring to  FIG. 4 , folding mobile phone  1  has upper unit  2  and lower unit  3 . Upper unit  2  has display  4  and lower unit  3  has input keys  5 . Units  2  and  3  are connected to each other by a hinge  6  that has two axis of rotation shafts that are capable of being opened, folded and turned. Operation input section  7  is arranged at the apex of the rotation shaft of hinge  6 . 
     Upper unit  2  can be opened through 180 degrees with respect to lower unit  3  via hinge portion  6 . 
       FIG. 5  shows a perspective view of a preferred embodiment showing rotation of upper unit  2  with respect to lower unit  3  of folding mobile phone  1  according to the present invention.  FIG. 6  is a perspective view of a preferred embodiment of folding mobile phone  1  when folding mobile phone  1  is in a folded state according to the present invention. 
     As shown in  FIGS. 5 and 6 , upper unit  2  can be turned through 180 degrees to the right and left horizontally with respect to lower unit  3  via hinge  6  from a perpendicularly opened state. 
     In this embodiment, display  4  can be exposed as shown in  FIG. 6 , even if folding mobile phone  1  is in a folded state. Further, folding mobile phone  1  has an operation input section  7  for operating display  4  in hinge  6 , so that folding mobile phone  1  can be used for playing a game and being easily operated by operation input section  7  even if folding mobile phone  1  is in a folded state. 
     The details of hinge  6  and the surrounding area of folding mobile phone  1  are explained below. 
       FIG. 7  is a perspective view of a preferred embodiment showing details of the interior structure of hinge  6  of folding mobile phone  1  according to the present invention. 
     In  FIG. 7 , hinge  6  includes a base  100 , a horizontal rotation shaft  101 , which is a first shaft member, and brackets  102  and  103 , which are second shaft members fixed at the right and left of horizontal rotation shaft  101  in the direction perpendicular to horizontal rotation shaft  101 . Base  100 , which is a base portion of hinge  6 , is fixed to lower unit  3 . Horizontal rotation shaft  101  is held by a central portion of base  100  to lower unit  2  so that it can rotate. 
     Mount  104  is provided between brackets  102  and  103 . Brackets  102  and  103  are fixed at an upper part of horizontal rotation shaft  101 , and are connected to each other under mount  104 . In the opening and closing shaft direction of bracket  103 , perpendicular opening and closing shaft  105  is provided for operating upper unit  2  so it can be opened and closed. Further, flexible board fixing member  110  is provided for fixing flexible board  106  and bobbin  107  for winding flexible board  106  around horizontal rotation shaft  101 . 
     Horizontal rotation shaft  101  is arranged on base  100  so that upper unit  2  is perpendicular to the face of input keys  5  on lower unit  3 , and so that it can be turned in the horizontal plane with respect to the face of input keys  5 . 
     Brackets  102  and  103 , which are the opening and closing shaft members at the upper part of horizontal rotation shaft  101 , and perpendicular opening and closing shaft  105  are fixed to upper unit  2 , so that upper unit  2  can be turned horizontally through 180 degrees to the right and left with respect to the face of input keys  5  of lower unit  3  by the rotating operation of horizontal rotation shaft  101 . 
     A space for mounting the aforementioned operation input section  7  is provided on the upper face of mount  104 . An input device such as a track ball or a pointing device according to the slide amount of key may be used as operation input section  7 . As the pointing device, for example, a device described in Japanese Patent Application Publication Laid-Open Kokai No. 2001-236351 may be used. However, the pointing device is not limited to the devices described in this publication. 
     Mount  104  may be mounted with an audio input device or an audio output device in addition to operation input section  7 . Also, a light emitting element may be mounted on mount  4 . The size of mount  104  is expandable in the lengthwise direction according to the device to be mounted thereon, by which a space capable of mounting the device can be secured. 
     Next, a connecting and attaching method using flexible board  106  for connecting a board of upper unit  2  to a board of lower unit  3  in hinge  6  will be explained. Flexible board  106  extending from a circuit board (not shown) of upper unit  2  is inserted into mount  104  in bracket  102  through a slot provided at an upper part of bracket  102  in a loose state with the flexible board being vertical. Herein, the loose state means the wound state shown in  FIG. 7 . Flexible board  106  passes through bracket  102  and mount  104  and is wound on bobbin  107 . An electrical path is formed by a part of flexible board  106  passing through mount  104  and is electrically connected to operation input section  7 . 
     Bobbin  107  is attached to the periphery of horizontal rotation shaft  101  has guide  108  at its upper part. Bobbin  107  does not rotate together with horizontal rotation shaft  101 . Bobbin  107  is fixed to lower unit  3  or base  100 . By winding flexible board  106  on bobbin  107 , flexible board  106  wound around horizontal rotation shaft  101  can be prevented from shifting in an axial direction. 
     Flexible board  106  wound on bobbin  107  is bent through 90 degrees so that it can be connected to a board of lower unit  3 , and a portion bent through 90 degrees is reinforced for high durability by flexible board fixing member  110 , which prevents flexible board  106  from floating. After being fixed by flexible board fixing member  110 , flexible board  106  is connected to a circuit board (not shown) of lower unit  3 . 
       FIG. 8  is an exploded perspective view of a preferred embodiment showing the relationship between hinge  6 , front cover  200  and back cover  201  of upper unit  2  in folding mobile phone  1  according to the present invention. In  FIG. 8 , guide  108  for bobbin  107 , as shown in  FIG. 7 , is omitted to make the figure understandable. 
     Front cover  200  and back cover  201  make up upper unit  2 . Front cover engagement portions  202  and  203  are formed separately from each other to connect front cover  200  to hinge  6  at the tip end on the hinge side of front cover  200 . Front cover engagement portion  202  is a cylinder having a substantially half moon shaped cross section, and flexible board  106  is arranged therein. Also, front cover engagement portion  202  is attached so that it can be fitted on a bush in the bracket  102 . Front cover engagement portion  203  is a cylinder without a notch, and perpendicular opening and closing shaft  105  is fixed therein. Perpendicular opening and closing shaft  105 , which is explained below, is inserted from one end of front cover engagement portion  203  from the rear and is fixed in a state in which front cover engagement portions  202  and  203  are connected to each other with brackets  102  and  103  being held therebetween, and is further fixed so that is can be turned with respect to bracket  103 . 
     Side cover portion  213 , cover member  212  and front cover engagement portion  202  restrain the movement of flexible board  104 , and side cover  211  covers one end of perpendicular opening and closing shaft  105 . 
       FIG. 9  is an enlarged perspective view of a preferred embodiment showing bracket  102  of a folding mobile phone according to the present invention. 
     In  FIG. 9 , bush  301  is a fixed shaft for supporting the rotation of upper unit  2  moving along with the rotation of perpendicular opening and closing shaft  105 , that is with the rotation due to opening and closing of upper unit  2 . Front cover engagement portion  202 , which is shown in  FIG. 8 , rotates while rubbing bush  301 . Front cover engagement portion  202  is rotated because the inside diameter of front cover engagement portion  202  is slightly larger than bush  301 . 
     When front cover engagement portion  202  engages with bush  301 , flexible board  106  of hinge portion  6  passes through bush  301  in bracket  102  and is wound in the cylinder of front cover engagement portion  202 , and thereby is connected to circuit board of upper unit  2 . 
       FIG. 10  is a perspective view of a preferred embodiment showing a state in which perpendicular opening and closing shaft  105  and bracket  103  are connected to each other in a folding mobile phone according to the present invention. 
     In  FIG. 10 , mount  104 , flexible board  106 , front cover  200 , and back cover  201  shown in  FIG. 5  are omitted. Bracket  103  adjoins front cover engagement portion  203 , which is shown in  FIG. 8 , when perpendicular opening and ciosing shaft  105  penetrates front cover engagement  203 . Front cover engagement portion  203  has a cylindrical shape as shown in  FIG. 8 , perpendicular opening and closing shaft  105  passes in front cover engagement portion  203 , head  401  of perpendicular opening and closing shaft  105  is embedded in a recess provided in advance in bracket  103 , and pin  410  is inserted from the upper part of bracket  103  to penetrate perpendicular opening and closing shaft  105 , by which head  401  (described below) is fixed to bracket  103 . The above method in which head  401  is fixed to bracket  103  is only one preferred embodiment. Other methods of fixing head  401  to bracket  103  can be used. 
       FIG. 11  is a perspective view of a preferred embodiment showing a state in which front cover  200  and back cover  201  are engaged with each other in a folding mobile phone according to the present invention. 
     Referring to  FIG. 11 , perpendicular opening and closing shaft  105  is inserted from one end of front cover engagement portion  203  and is fixed to bracket  103  by pin  410 , and then back cover  201  is fitted to front cover  200 . 
     In this embodiment, flexible board  106 , in a loose state, is arranged in a space on one side (bracket  102  side) in the opening and closing shaft direction of brackets  102  and  103 , which are the opening and closing shaft members, and perpendicular opening and closing shaft  105  is arranged on the other side (bracket  103  side) in the opening and closing shaft direction of brackets  102  and  103 . Therefore, flexible board  106  does not need to be wound around the shaft. Also, since flexible board  106  does not interfere with perpendicular opening and closing shaft  105 , the diameters of front cover engagement portions  202  and  203  can be decreased, and the diameter of the hinge can be decreased. 
       FIG. 12  ( a ) is an exploded view showing a construction of perpendicular opening and closing shaft  105  and  FIG. 12  ( b ) is a sectional view of a front cover engagement portion  203  in a folding mobile phone according to the present invention. 
     Perpendicular opening and closing shaft  105  for perpendicularly rotating (opening and closing) operation of upper unit  2  with respect to lower unit  3  is inserted in the cylindrical portion of the front cover engagement portion  203 . In the perpendicularly rotating (opening and closing) operation, upper unit  2  can be turned within 180 degrees with respect to lower unit  3  with a shaft  402  shown in  FIG. 12  ( a ) serving as a central axis. Perpendicular opening and closing shaft  105  is made up of shaft  402 , which is the center-of rotation, head  401  for turning shaft  402 , fixed cam A  403  fixed to shaft  402 , rotating cam A  404  paired with fixed cam A  403 , rotating cam B  406  fixed to shaft  402 , fixed cam B  407  paired with rotating cam B  406 , spring  405  for pressing rotating cam A  404  and rotating cam B  406  against fixed cam A  403  and fixed cam B  407 , respectively, and cover  408  for covering these elements. 
     Cover  408  of perpendicular opening and closing shaft  105  has a non-circular cross section so that the movement of perpendicular opening and closing shaft  105  is directly transmitted to the front cover engagement portion  203  as shown in  FIG. 8 . The shape of the cross section of cover  408  is not subject to any special restriction if the shape is such that cover  408  engages with front cover engagement portion  203  and hence the rotation of perpendicular opening and closing shaft  105  is transmitted to upper unit  2 . 
     Next, the operation of perpendicular opening and closing shaft  105  will be explained. Rotating cam A  404  is fixed to shaft  402  and is rotated together with shaft  402 . Fixed cam A  403  fixed to cover  408  and rotating cam A  404  are provided so that rotating cam A  404  and fixed cam A  403  are engaged with each other when upper unit  200  is in a closed (0 degree) state to produce suction torque of the closed side (0 degree). Similarly, fixed cam B  407  fixed to cover  408  and rotating cam B  406  are provided so that rotating cam B  406  and fixed cam B  407  are engaged with each other when upper unit  200  is in an opened (180 degree) state to produce suction torque of the opened side (180 degree). 
     Next, the assembly of perpendicular opening and closing shaft  105  will be explained. The tip end of shaft  402  is installed in head  401 , and shaft  402  is caused to pass through a hole formed in the cover  408 , by which an exposed portion of shaft  402  is covered with cover  408 . Subsequently, fixed cam A  403 , rotating cam A  404 , spring  405 , rotating cam B  406 , and fixed cam B  407  are slipped onto shaft  402  in succession. After all elements are assembled, shaft  402  is caulked, which fixes shaft  402  so that it does not to come off. 
     The connecting relationship between perpendicular opening and closing shaft  105  and bracket  103  as shown in  FIG. 10  will now be described. After head  301  of perpendicular opening and closing shaft  105  is arranged in a concave portion provided in bracket  103 , perpendicular opening and closing shaft  105  is connected to bracket  103  with pin  401  as shown in  FIG. 10  so that pin  410  penetrates perpendicular opening and closing shaft  105  from the upper part of bracket  103 . Head  401  of perpendicular opening and closing shaft  105  and shaft  402  each are formed with through hole  409  for causing pin  410  to penetrate to fix perpendicular opening and closing shaft  105  to bracket  103  at this time. By the connection of perpendicular opening-and closing shaft  105  and bracket  103 , head  401  and shaft  402  of perpendicular opening and closing shaft  105  are connected to bracket  103 , so that head  401  and shaft  402  are fixed during the opening and closing operation. When upper unit  2  is opened or closed by perpendicular opening and closing shaft  105 , fixed cam A  403 , rotating cam A  404 , spring  405 , rotating cam B  406 , fixed cam B  407  and cover  408  other than head  401  and shaft  402  are operated together with upper unit  2 . 
     In this embodiment, perpendicular opening and closing shaft  105  is fixed to bracket  103  by inserting pin  401  in perpendicular opening and closing shaft  105  fixed to bracket  103  from upper part of bracket  103 . However, perpendicular opening and closing shaft  105  may be attached to bracket  103  using pressure by providing perpendicular opening and closing shaft  105  fixing portion on lower unit  3  and by pressing perpendicular opening and closing shaft  105  from the outside. 
     In the above-described embodiment, since front cover engagement portion  203  of front cover  200  has a closed cylindrical shape as shown in  FIG. 8 , when perpendicular opening and closing shaft  105  is installed, as shown in  FIG. 8 , it is necessary to insert perpendicular opening and closing shaft  105  in front cover engagement portion  203 . However, if front cover engagement portion  203  has an accurate cross section, front cover  200  can be fitted over perpendicular opening and closing shaft  105  after perpendicular opening and closing shaft  105  is fixed in advance to bracket  103 . 
     Also, perpendicular opening and closing shaft  105  may be configured so that it is fixed to back cover  201 , and not to front cover  200 . In any case, any configuration can be used in which perpendicular opening and closing shaft  105  rotates integrally around an opening and closing shaft along with the opening and closing of upper unit  2 . 
     Also, in this embodiment, the horizontal rotation shaft  101  is arranged so that it is vertical with respect to the face of input key  5  and is provided so that it can be rotated in a horizontal plane with respect to the face of input key  5 , and the opening and closing shaft members (brackets  102  and  103 ) are fixed to horizontal rotation shaft  101 . However, the present invention is not limited to this configuration. For example, the configuration may be such that horizontal rotation shaft  101  is not rotated and is fixed to base  101 , and brackets  102  and  103 , which are opening and closing shaft members, are fixed to horizontal rotation shaft  101  and turn in the horizontal plane around the non-rotating horizontal rotation shaft. 
     The above description of an embodiment of this invention has been made by taking a mobile phone by way of example. However, the invention is not limited to a mobile phone. The present invention can also be applied to any personal digital assistant in which the operating section and the display section are separated so that they can be foldable and the operation input section can be mounted on the horizontal rotation shaft, and can achieve the same advantages. 
     The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by the limitations of the claims and equivalents.

Summary:
A folding electric has an upper unit and lower unit. A hinge connects the upper unit to the lower unit. The hinge includes at least a perpendicular opening and closing shaft to open and close the upper unit with respect to the lower unit and a horizontal rotation shaft, fixed vertically to the surface of the lower unit, to rotate the upper unit with respect to the lower unit coming in contact with each other.