Patent Abstract:
A computer apparatus includes a base and a display device. The base includes a first casing and a ferromagnetic unit fastened to the first casing. The display device includes a second casing having a connecting side portion and a magnetic unit. In a first use state, the connecting side portion of the second casing is adjacent to the first casing of the base, and an angle formed therebetween is adjustable. The magnetic unit is fastened to the connecting side portion of the second casing, and magnetically attracts ferromagnetic unit of the base, thereby permitting sliding of the display device relative to the base without separating therefrom.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority of Taiwanese Application No. 101132148, filed on Sep. 4, 2012, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a computer apparatus, more particularly to a computer apparatus having a display device slidable with respect to a base. 
         [0004]    2. Description of the Related Art 
         [0005]    The main components of a notebook computer or a tablet PC with an expansion device includes a base and an adjustable display screen for adjusting the operational angle of the display screen with respect to the base. A current base for a notebook computer is a host used with a keyboard unit. A current base for a tablet PC is an accessory adapted for connecting a keyboard module and/or a charging module to the tablet PC. 
         [0006]    Generally speaking, the base and the display screen are pivotally interconnected. Various designs have emerged in the market, including ones with display screens slidable relative to a base. However, the sliding mechanism in most of those slidable designs relies on providing slide grooves in the base, and wheels on the display screen. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the present invention is to provide a computer apparatus that uses magnetism to enable relative sliding movement between a base and a display screen. 
         [0008]    According to the present invention, there is provided a computer apparatus comprising a base and a display device. 
         [0009]    The base includes a first casing and a ferromagnetic unit disposed on the first casing. 
         [0010]    The display device is slidably disposed on and above the base, and includes a second casing that has a connecting side portion, a display panel disposed on the second casing, and a magnetic unit fastened to the connecting side portion of the second casing for attracting the ferromagnetic unit. Ina first use state of the computer apparatus, the connecting side portion of the second casing is connected to the first casing of the base at an operational angle. Specifically, the ferromagnetic unit of the first casing and the magnetic unit of the second casing are magnetically attracted to each other to prevent separation of the display device from the base. 
         [0011]    The display device further includes a plurality of spaced-apart wheels installed along the connecting side portion of the second casing to facilitate the sliding movement of the display device relative to the base. A surface of each of the wheels slightly protrudes from the connecting side portion. Further, the plurality of wheels and the magnetic unit may be integrated as a single entity. 
         [0012]    The magnetic unit of the display device includes a plurality of cylindrical magnet members fastened to the connecting side portion. The width between the ferromagnetic units of the first casing is not smaller than the distance between outer ends of two outermost ones of the cylindrical magnet members of the second casing. 
         [0013]    The ferromagnetic unit is an iron plate disposed on the first casing. Alternatively, the ferromagnetic unit is a magnetic layer formed on a surface of the first casing, for example, by electroplating, laying iron powder on, or laying magnetic powder on the surface of the first casing. 
         [0014]    The computer apparatus further comprises a support frame having two ends respectively and pivotally connected to a rear end of the first casing of the base and the display device the display device. 
         [0015]    The computer apparatus further comprises a pair of slide seats disposed respectively on two opposite sides of the base and pivotally connected to the display device. The first casing of the base has an upper surface, two side surfaces connected respectively to two opposite sides of the upper surface, and two slide slots formed respectively in the two side surfaces in a front-rear direction. Each of the slide seats has an upper plate body superposed on the upper surface of the base, a lower plate body extending into a respective one of the slide slots, and a connecting plate body connecting the upper plate body to the lower plate body. Further, each of the slide seats includes a bearing disposed on the upper plate body that has a hole. 
         [0016]    The display device further includes two side support rods fixedly and respectively coupled to two opposite sides of the second casing, two pivot rods protruding respectively from the side support rods toward each other and adjacent to the connecting side portion of the second casing, and a plurality of washers sleeved on each of the pivot rods. Each of the pivot rods respectively extends through the hole of a corresponding one of the bearings such that at least two of the washers are clamped between the corresponding bearing and the corresponding side support rod. The washers provide a frictional resistance between the side support rods and the bearings for maintaining an operational angle between the display device and the base. Each of the bearings is disposed on a front end of the upper plate body of the respective slide seat, and further has a lock bolt that extends through a rear end of the upper plate body of the corresponding slide seat for maintaining the position of the corresponding slide seat relative to the base. 
         [0017]    The second casing of the display device further includes a receiving slot formed in the connecting side portion. Additionally, the computer apparatus further includes a rotation mechanism having a rotation seat that is accommodated by the receiving slot and that can rotate to project from the receiving slot. Further, the magnetic unit also has a magnet member fastened to the rotation seat. 
         [0018]    Moreover, the rotation mechanism has a resilient member having a fixed end secured to the second casing and a rotary end secured to the rotation seat. The resilient member provides a restoring force for pivoting and retracting the rotation seat into the receiving slot. The second casing of the display device further has a first surface facing in the same direction as the display panel, a second surface opposite to the first surface, and a slot bottom surface parallel to the first surface, and a slot peripheral surfaces extending from the slot bottom surface to the first surface for defining the receiving slot. The rotation mechanism further has two spaced-apart fixed frames protruding from the slot bottom surface. The rotation seat has a block-shaped body situated between the two fixed frames, and two rotary shafts extending respectively from the two sides of the block-shaped body and connected respectively and pivotally to the fixed frames. 
         [0019]    Additionally, the rotation seat of the rotation mechanism has a spring hole for accommodating the rotary end of the resilient member. The rotation mechanism includes a stop rib protruding from the slot bottom surface of the second casing and having one end adjacent to one of the two fixed frames for confining the fixed end of the resilient member between the stop rib and the one of the two fixed frames, thereby securing the fixed end of the resilient member to the second casing. The rotation mechanism further includes a limiting unit has a positioning peg that extends from a respective fastening unit and that limits the rotational angle of the rotation seat, and an arc-shaped positioning groove formed on an end of the block-shaped body for accommodating the positioning peg. 
         [0020]    When the positioning peg is disposed at an end of the arc-shaped positioning groove, the rotation seat is accommodated by the receiving slot. When the positioning peg is disposed at an opposite end of the arc-shaped positioning groove, the rotary shafts project from the receiving slot. 
         [0021]    The base includes a long, shallow groove formed in the upper surface of the first casing and extending in the front-rear direction for accommodating a ferromagnetic unit formed of an iron plate that corresponds in shape to the shallow groove. The magnetic unit of the display device is aligned with the shallow groove. 
         [0022]    The magnetic attractive force between the magnetic unit and the ferromagnetic unit is nonpolar. 
         [0023]    As such, the present invention relies on the magnetic attraction between a ferromagnetic unit on the first casing of the base and a magnetic unit situated in a corresponding position on the second casing of the display device to allow the display device to slide with respect to the base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
           [0025]      FIG. 1  is a perspective view of the first embodiment of a computer apparatus according to the present invention; 
           [0026]      FIG. 2  is an exploded perspective view of the computer apparatus in  FIG. 1 ; 
           [0027]      FIG. 3  is an enlarged fragmentary perspective view of the connection between a display device and a base of the embodiment of  FIG. 1 ; 
           [0028]      FIG. 4  to  FIG. 6  are perspective views illustrating sliding movement of the computer apparatus from a first use state to a second use state; 
           [0029]      FIG. 7  is a perspective view showing the computer apparatus with the display device separated from the base; 
           [0030]      FIG. 8  and  FIG. 9  are perspective views of a variant of the first embodiment, wherein the display device completely covers the base at a second use state; 
           [0031]      FIG. 10  is an enlarged view of a variant of a wheel used in the first embodiment; 
           [0032]      FIG. 11  is a perspective view of the second embodiment of a computer apparatus according to the present invention; 
           [0033]      FIG. 12  is an enlarged fragmentary perspective view illustrating a connection between a slide seat and a base; 
           [0034]      FIG. 13  is a perspective view of the third embodiment of a computer apparatus according to the present invention; 
           [0035]      FIG. 14  is an exploded perspective view of the third embodiment; 
           [0036]      FIG. 15  is an enlarged, exploded y perspective view of a rotation mechanism of the third embodiment 3; 
           [0037]      FIG. 16  is an enlarged perspective view of a block-shaped body of a rotation mechanism viewed from an angle different from that in  FIG. 15 ; 
           [0038]      FIG. 17  and  FIG. 18  are enlarged fragmentary perspective views of the rotation mechanism in the retracted and extended states, respectively; and 
           [0039]      FIG. 19  and  FIG. 20  are side views illustrating the ability to adjust the operational angle of the display device with respect to the base. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
         [0041]    With reference to  FIG. 1 , the first embodiment of a computer apparatus  100  of the present invention includes a base  1 , a display device  2  situated on and above and slidable relative to the base  1 , and a support frame  3  pivotally connected between the base  1  and the display device  2 . 
         [0042]    In this embodiment, as non-limiting examples, the display device  2  is a tablet PC, and the base  1  is an expansion keyboard for the tablet PC. Alternatively, the display device  2  may be the screen of a notebook computer and the base  1  a host of the notebook computer. 
         [0043]    With further reference to  FIG. 2 , the base  1  includes a first casing  11 , a ferromagnetic unit, and a keyboard  13 . In this embodiment, the ferromagnetic unit is an iron plate  12  disposed on and above the first casing  11 , and has a primary portion  120  covering a rear portion of the first casing  11 . Alternatively, the ferromagnetic unit may be an iron plate disposed on the underside of the first casing  11 , or a magnetic layer disposed on the surface of the first casing  11 , formed, for example, by electroplating, laying iron powder on or laying magnetic powder on the surface of the first casing, or using magnetic material for manufacturing the first casing  11  (i.e., unifying the first casing  11  and the ferromagnetic unit). The keyboard  13  is exposed from a front portion of the first casing  11 . 
         [0044]    The display device  2  includes a second casing  21 , a display panel  22  exposed from the second casing  21 , a magnetic unit  23  fastened to the second casing  21  and aligned with the iron plate  12  on the first casing  11 , and a pair of spaced-apart wheels  24  situated at two sides of the magnetic unit  23 , respectively. 
         [0045]    The second casing  21  has a first surface  211  facing in the same direction as the display panel  22 , a second surface  212  opposite to the first surface  211 , and a connecting side portion  213  adjacent to the first casing  11 . With reference to  FIGS. 4 and 5 , when the computer apparatus  100  is in a first use state, the connecting side portion  213  of the second casing  21  adjoins an upper surface of the first casing  11 , which forms an adjustable operational angle θ between zero and 180 degrees. With reference to  FIG. 6 , when the computer apparatus  100  is in a second use state, the second surface  212  of the second casing  21  lays flat against the first casing  11  of the base  1 , in such a manner that the keyboard  13  remains exposed from the second casing  21 , and the first surface  211  of the second casing  21  and the upper surface of the first casing  11  are parallel to each other. When the computer apparatus  100  is in a non-use state (not shown), the first surface  211  of the second casing  21  lays flat against the first casing  11  of the base  1  so that the angle θ is zero. 
         [0046]    The magnetic unit  23  includes a plurality of cylindrical magnet members  231  affixed to the connecting side portion  213  of the second casing  21 . Any two adjacent ones of the cylindrical magnet members  231  may abut against or spaced-apart from each other so long as the width of the iron plate  12  is not less than the overall width of an assembly of the plurality of cylindrical magnet members  231 . 
         [0047]    The wheels  24  are installed on the connecting side portion  213  of the second casing  21 , and are located at two sides of the magnetic unit  23  for facilitating sliding movement of the display device  2  relative to the base  1 . The cylindrical magnet members  231  are flush against the surface of the connecting side portion  213 , and are magnetically attracted to the iron plate  12 , thus drawing the first casing  11  and the second casing  21  together. Because each wheel  24  protrudes slightly from the connecting side portion  213  (see  FIG. 3 ), and because the cylindrical magnet members  231  are flush against the connecting side portion  213 , only the wheels  24  of the display device  2  make contact with the base  1 , which allows the display device  2  to slide more easily with respect to the base  1 . 
         [0048]    Alternatively, with reference to  FIGS. 2 and 10 , this embodiment may use wheels  24 ′ as shown in  FIG. 10  that have torque instead of the torqueless wheels as shown in  FIG. 2 . A display device using the wheels  24 ′ can slide at a controlled speed and maintain a desired position due to the resistance created in the wheels  24 ′. 
         [0049]    Specifically, each wheel  24 ′ has an axle  241  fixed to the second casing  21 , a rotary body  242  sleeved rotatably on the axle  241 , a first frictional pad  243  affixed to a side surface  2421  of the rotary body  242 , a second frictional pad  244  fixedly sleeved on the axle  241  for providing frictional resistance against the first frictional pad  243 , a plurality of leaf springs  245  sleeved on the axle  241  and adjacent to the second frictional pad  244 , and a retainer unit  246  for retaining the rotary body  242 , the first frictional pad  243 , the second frictional pad  244 , and the leaf springs  245  along the axle  241  together. The retaining unit  246  is operable to adjust the biasing force of the left spring  245  for pressing the second frictional pad  244  against the first frictional pad  243 . 
         [0050]    The support frame  3  is pivotally connected to a rear end  111  of the first casing  11  of the base  1  at an end thereof, and has a free end  31  extending toward the display device  2 . The free end  31  is pivotally connected to the second surface  212  of the second casing  21 . In this embodiment, at least one of the pivotal connections between the support frame  3  and the display device  2  and between the support frame  3  and the base  1  utilizes a torque control mechanism, such as friction pads (not shown), to increase the frictional resistance between the connected elements, to maintain the relative positions of the display device  2  and the base  1 , thereby facilitating angle adjustment of the display device  2 . 
         [0051]    With reference to  FIGS. 8 and 9 , the length of the support frame  3  in this embodiment may be modified to be longer than shown in  FIGS. 5 and 6 . In the first use state of the computer apparatus  100  (see  FIG. 8 ), the first surface  211  of the second casing  21  and the first casing  11  of the base  1  form an angle θ. In the second use state of the computer apparatus  100  (see  FIG. 9 ), the second surface  212  of the second casing  21  lays flat against and completely covers the first casing  11  of the base  1  such that the keyboard  13  is also covered. 
         [0052]    With reference to  FIG. 7 , using a tablet PC as an example of the display device  2 , when the user desires to remove the display device  2  from the base  1 , he/she need only overcome the magnetic attractive force between the plurality of cylindrical magnet members  231  and the iron plate  12 . The support frame  3  is detachable from the display device  2 , allowing the second casing  21  of the display device  2  to completely separate from the first casing  11  of the base  1 . 
         [0053]    With reference to  FIGS. 11 and 12 , the second embodiment of the present invention is similar to the first embodiment, except that the computer apparatus  200  includes a pair of slide seats  4 , and does not include a support frame  3  (see  FIG. 1 ). The slide seats  4  are disposed respectively on two opposite sides of the base  1 , and are pivotally connected to the display device  2 . 
         [0054]    Specifically, for engaging the slide seats  4 , the base  1  includes an upper surface  14 , two side surfaces  15  connected to the sides of the upper surface  14 , respectively, and two slide slots  16  formed respectively along the two side surfaces  15  in the front-to-rear direction. Each slide seat  4  is slidable within the corresponding slide slot  16 , and has an upper plate body  41  disposed on and above the upper surface  14  of the base  1 , a lower plate body  42  extending into the corresponding slide slot  16 , a connecting plate body  43  connecting the upper plate body  41  to the lower plate body  42 , and a bearing  44  that protrudes upwards out of a front end  411  of the upper plate body  41  and that has a hole  440  extending through the bearing  44  in a left-to-right direction. 
         [0055]    The display device  2  also includes two side support rods  251  fixedly coupled to respective sides of the second casing  21 , two pivot rods  252  protruding respectively from the side support rods  251  toward each other, adjacent to the connecting side portion  213  of the second casing  21 , and extending respectively through the holes  441  of the bearings  44 , and a plurality of washers  253  sleeved on each pivot rod  252 . At least two of the washers  253  are clamped between the corresponding bearing  44  and the corresponding side support rods  251  to provide frictional resistance against pivotal movement of the display device  2  such that, when no force is exerted against the display device  2 , the operational angle with respect to the base  1  can be maintained. To adjust the operational angle between the base  1  and the display device  2 , a user must overcome the frictional resistance between the washers  253 , the side support rods  251 , and the bearings  44 . 
         [0056]    Additionally, each slide seat  4  further has a lock bolt  45  that extends through a rear end  412  of the upper plate body  41  for maintaining the position of the corresponding slide seat  4  relative to the base  1 . When display device  2  together the slide seats  4  is moved to a desired position, the lock bolt  45  is operable to lock the display device  2  on the base  1 . 
         [0057]    Importantly, the wheels  24  of the previous embodiments may also be integrated with the magnetic unit  23 , for example, by installing one or many magnet pieces (not shown) on or within each wheel  24 . By housing a magnet piece within the wheel  24 , the wheel  24  is able to not only slide with respect to the base  1 , but also generate a magnetic force with respect to the base  1 , thus negating the need for a separate magnetic unit  23  on the connecting side portion  213  of the display device  2 . 
         [0058]    With reference to  FIGS. 13 and 14 , the third embodiment of a computer apparatus  300  of the present invention is similar to the first embodiment, except that the display device  2  includes a mobile magnetic unit  23 . To clarify, the display device  2  uses a rotatable magnetic unit  23  to both maintain its position and adjust its angle by sliding relative to the base  1 . The wheels  24  of the first embodiment may still be used to facilitate relative sliding movement between the display device  2  and the base  1 . Alternatively, it is also possible to omit the wheels  24  from the display device  2  and depend primarily on the magnetic unit  23  to maintain contact between the display device  2  and the base  1  for allowing relative sliding movement thereof. 
         [0059]    It should be noted that the following description of the magnetic unit  23 , the ferromagnetic unit, and an associated rotating means of the magnetic unit  23  is of a symmetrical design, but this does not limit the scope of this invention thereto. For example, the computer apparatus  100  may includes only a single magnet  232  installed in the middle of the display device  2  and the base  1 , and a single iron plate  12  disposed on the middle of the base  1 . 
         [0060]    The base  1  includes a pair of shallow grooves  17  disposed respectively in two sides of the upper surface  14  of the first casing  11  and each extending in the front-to-rear direction for accommodating an iron plate  12 . Each magnetic unit  23  of the display device  2  is positioned accordingly to attract the corresponding iron plate  12  housed by the corresponding shallow groove  17 . Alternatively, as in the first embodiment, each ferromagnetic unit may include an iron plate disposed on the underside of the first casing  11 , a magnetic layer disposed on the surface of the first casing  11 , for example, by electroplating, laying iron powder on or laying magnetic powder on the surface of the first casing, or unification of the first casing  11  and the ferromagnetic unit by using a magnetic material to manufacture the first casing  11 . 
         [0061]    With reference to  FIG. 15 , the second casing  21  of the display device  2  of the third embodiment also has a pair of spaced-apart receiving slots  214  formed respectively at the left and right ends of the connecting side portion  213  and a pair of slot covers  217  for covering the receiving slots  214 , respectively. Each receiving slot  214  is defined by a slot bottom surface  215  parallel to the first surface  211 , and a slot peripheral surface  216  extending from a periphery of the slot bottom surface  215  to the first surface  211  and aligned with the corresponding shallow groove  17 . 
         [0062]    The computer apparatus  300  further includes a pair of rotation mechanisms  5  respectively installed in the receiving slots  214 . Each rotation mechanism  5  has a rotation seat  51  that is accommodated by the corresponding receiving slot  214  and that can rotate to project from the receiving slot  214 , a resilient member  52 , two spaced-apart fixed frames  53  protruding from the slot bottom surface  215 , a limiting unit  54  for limiting the rotational angle of the rotation seat  51 , and a stop rib  55  protruding from the slot bottom surface  215  of the second casing  21  that has one end adjacent to one of said two fixed frames  53 . 
         [0063]    Each rotation seat  51  has a block-shaped body  511  situated between the two fixed frames  53 , two rotary shafts  512  extending respectively from the two sides of the block-shaped body  511  away from each other and connected respectively to the fixed frames  53 , amounting slot  513  formed in the block-shaped body  511 , and a spring hole  514  formed in one side of the block-shaped body  511  (shown at the right side of  FIG. 15 ). 
         [0064]    The magnetic unit  23  in this embodiment includes two magnet members  232  secured respectively in the mounting slots  513  of the rotation seats  51 . The positions of the magnet members  232  correspond respectively with those of the iron plates  12  in the shallow grooves  17 . When the ferromagnetic unit is of a different design, the positions of the iron plates  12  may be adjusted accordingly. Additionally, the shape of the magnet members  232  and the manner in which they are secured are not limited by those which are shown in the figures or what is discussed above, so long as the magnet members  232  are fastened respectively to the rotation seats  51 . 
         [0065]    The resilient member  52  of each rotation mechanism  5  includes a rotary end  522  inserted into the spring hole  514  of the corresponding rotation seat  51  and a fixed end  521  affixed to the second casing  21  of the display device  2 . As such, each of the resilient members  52  provides a restoring force for pivoting and retracting the corresponding rotation seat  51  into the corresponding receiving slot  214 . The fixed end  521  of each resilient member  52  is confined between one end of the stop rib  55  and the adjacent fixed frame  53 , thereby securing the fixed end  521  of the corresponding resilient member  52  to the second casing  21 . 
         [0066]    With reference to  FIGS. 15 and 16 , the limiting unit  54  of each rotation mechanism  5  has a positioning peg  541  extending from one of the fastening units  53 , and an arc-shaped positioning groove  542  formed in a side of the block-shaped body  511  of the corresponding rotation seat  51  for receiving the positioning peg  541  Such that, when the positioning peg  541  is disposed at an end of the positioning groove  542 , the corresponding rotation seat  51  is completely accommodated within the receiving slot  214 , as shown in  FIG. 17 . When the positioning peg  541  is disposed at an opposite end of the positioning groove  542 , the corresponding rotation seat  51  projects from the receiving slot  214  as shown in  FIG. 18 . At most, the rotary pegs  512  can rotate to the opposite end of the arc-shaped positioning groove  542 , which thus limits the ability of the rotation seat  51  to leave the receiving slot  214 . 
         [0067]    As in the first embodiment, the display device  2  is detachable from the support frame  3 . With reference to  FIGS. 14 ,  17  and  18 , when the display device  2  is a tablet PC and used independently from the base  1 , the rotation seat  51  is biased by the resilient member  52  to rotate into a completely concealed state (i.e., rotate completely into the corresponding receiving slot  214 ), as in  FIG. 17 , so as to maintain the outer appearance of the tablet PC. If the rotation seat  51  approaches to the ferromagnetic unit (such as an iron plate  12 ), it will rotate in the corresponding receiving slot  214  due to the magnetic attractive force between the magnet members  232  and the ferromagnetic unit. 
         [0068]    With reference to  FIGS. 14 ,  19  and  20 , when the magnet members  232  of the display device  2  attract the iron plates  12  of the base  1 , the display device  2  may be operated to allow the connecting side portion  213  to slide back and forth along the iron plates  12  to adjust the operational angle, as shown in  FIGS. 19 and 20 . As in the first embodiment, the operational angle of the display device  2  in this embodiment is maintained by the torque control of the support frame  3 . However, maintenance of the operational angle should not be limited to torque control of the support frame  3 . Alternatively, the torque design may be a resistance device implemented in the rotation mechanism  5 . 
         [0069]    To sum up, the present invention combines a ferromagnetic unit disposed on the first casing  11  of the base  1  with a magnetic unit  23  disposed on the second casing  21  of the display device  2 , and uses the attractive force between the ferromagnetic unit and the magnetic unit to facilitate relative sliding movement between the base  1  and the display device  2 . Of course, as can easily be seen by one skilled in the art, the positions of the ferromagnetic unit and the magnetic unit  23  are interchangeable. That is, the ferromagnetic unit is disposed on the second casing  21  and the magnetic unit  23  is disposed on the first casing  11 . Additionally, the magnetic attractive force between the magnetic unit  23  and the ferromagnetic unit does not depend on polarity. This means that if the magnetic unit  23  has north and south poles, the ferromagnetic unit can be manufactured from nonpolar, magnetically attractable material in the form of iron plate  12  or iron powder. This allows the magnetic unit  23  and ferromagnetic unit continuously attract rather than attract and repulse each other, which maintains stable and steady relative sliding movement between the base  1  and the display device  2 . 
         [0070]    While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.

Technology Classification (CPC): 6