Patent Publication Number: US-7224580-B2

Title: Exterior enclosure for portable information processor, method of manufacturing the same, and portable information processor using the enclosure

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an exterior enclosure for housing a portable information processor, such as a notebook-size computer and a personal digital assistance, and to a method of manufacturing the enclosure. 
     2. Background Art 
     Recently, improvements have been made in providing lightweight portable information processors, such as a notebook-size computer and a personal digital assistance. Under these circumstances, a lightweight and strong material such as magnesium alloy has come to be widely used in producing the exterior enclosure of a display section incorporating therein a liquid crystal display device. Further, in the manufacture of such a exterior enclosure, a method of press forming of plate material capable of producing thinner walled products to achieve reduction in weight has come to be adopted rather than a method of manufacturing them by melt-shaping, such as magnesium die-casting. 
       FIG. 4  is a sectional view of the display section of a conventional portable information processor. This drawing illustrates a structure based on the design values. Enclosure back panel  31  covers liquid crystal display device  32  from behind. Enclosure back panel  31  has elevated portion  31 A raised along ridge lines  31 B. Elevated portion  31 A has its surface formed flat to provide top plane  31 C. In front of liquid crystal display device  32 , there is disposed enclosure front panel  33 . 
     Such a structure as described above is called a bonnet structure. The bonnet structure is used when fabricating an enclosure with a thin-walled material. When fabricated in a bonnet structure, the strength of enclosure back panel  31  is enhanced. An example in which such a bonnet structure is applied to an enclosure of a portable information processor is disclosed, for example, in Unexamined Japanese Patent Publication No. 2003-204174. 
     Fabrication sequence of enclosure back panel  31  in the press forming process will be described below.  FIG. 5  is a schematic diagram showing a process for fabricating enclosure back panel  31  by the press forming method. Plate-shaped blank material  44  of magnesium alloy is sandwiched between blank holder  46  and die set  43  and pressed down by punch  42 , in a condition heated by heater  45 . 
     At the time when elevated portion  31 A is formed by press forming, however, a material distortion occurs around ridge line  31 B. Accordingly, elevated portion  31 A is deviated from flatness and deformed wavy. In cases where the material is magnesium alloy, it is generally practiced to perform the press forming operation at temperatures above 200° C. to prevent cracks from being formed due to bending the material. During the course of this heating, thermal expansion occurs in the material. Therefore, when a material as above is used, volume of the material becomes more than that of necessity in particular, and hence elevated portion  31 A is deformed into a sagged and swelled shape.  FIG. 6  is a sectional view of enclosure back panel  31  in which such a shape is represented with exaggerated dimensions for the sake of explanation. The difference between the convexed and concaved levels in actuality is only around ±0.5 mm. However, when the surface is deformed to have irregular concavity and convexity, it impairs the appearance. In addition, the convexed portion is easily dented when subjected to a slight external force. Thus, the surface loses its tautness and its dent resistance is significantly deteriorated. 
     SUMMARY OF THE INVENTION 
     An exterior enclosure of the present invention has an elevated portion providing a top plane thereon. The elevated portion is surrounded by two pairs of opposed ridge lines. The top plane has a concavely curved surface with respect to one of the pairs of ridge lines. This structure enhances the strength of the top plane. Such an exterior enclosure is fabricated by a process in which a plate-shaped metallic blank is fixed in place and then pressed in a heated condition such that the elevated portion constituting the top plane is shaped. In shaping the elevated portion, it is arranged such that the elevated portion has a concavely curved surface with respect to one of the two pairs of ridge lines. Thus, occurrence of the material distortion due to the press-forming fabrication method and formation of the concavity and convexity on the elevated portion caused by thermal expansion due to the press forming carried out at high temperatures can be prevented. As a result, a stable shape can be secured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a sectional view of a display section of a portable information processor according to an embodiment of the present invention. 
         FIG. 1B  is an enlarged perspective view of a main portion of an enclosure back panel of the display section shown in  FIG. 1A . 
         FIG. 2A  is a perspective view of the portable information processor employing the enclosure back panel according to the embodiment of the present invention. 
         FIG. 2B  is a block diagram of the portable information processor shown in  FIG. 2A . 
         FIG. 3  is a schematic diagram of a process in which the enclosure back panel shown in  FIG. 1A  is fabricated by a press forming fabrication method. 
         FIG. 4  is a sectional view of a structure of a display section based on design values of a conventional portable information processor. 
         FIG. 5  is a schematic diagram of a process in which a conventional enclosure back panel is fabricated by a press forming fabrication method. 
         FIG. 6  is a sectional view showing a conventional enclosure back panel in exaggerated dimensions to explain its shape. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1A  is a sectional view of a display section of a portable information processor according to an embodiment of the present invention.  FIG. 1B  is an enlarged perspective view of a main portion of an enclosure back panel of the display section shown in  FIG. 1A . Display section  4  has liquid crystal display device (hereinafter referred to as “display device”)  2 , enclosure back panel  1 , and enclosure front panel  3 . Enclosure back panel  1  as an exterior enclosure covers display device  2  from behind. On the upper surface side of enclosure back panel  1 , there is provided elevated portion  1 A raised along ridge lines  1 B. Elevated portion  1 A forms top plane  1 C. Elevated portion  1 A is surrounded by a first pair of ridge lines  1 B and a second pair of ridge lines  1 D adjoining first ridge lines  1 B. In front of display device  2 , there is disposed enclosure front panel  3 . In other words, enclosure front panel  3  and enclosure back panel  1  are fixed together with display device  2  sandwiched in between. 
     Enclosure back panel  1  is preferably fabricated by a press forming method of a plate material of magnesium alloy having a thickness of 0.5-0.7 mm to realize a lightweight and high strength panel. The provision of elevated portion  1 A enhances the strength of enclosure back panel  1  made of such a thin-walled metal plate. Top plane  1 C of elevated portion  1 A has a concavely curved surface downward from ridge lines  1 B. It is preferred that the curved surface is a cylindrical face as shown in  FIG. 1B . In other words, it is preferred that mutually opposed two ridge lines  1 D have coaxial cylindrical arc shapes. Such shapes are exaggeratedly depicted in  FIGS. 1A and 1B . Although the difference in level between ridge line  1 B and the bottom of the concaved portion is 0.4 mm to 0.6 mm, it is substantially unnoticeable by sight inspection because the curved surface is formed with a constant curvature. 
       FIG. 2A  is a perspective view of a portable information processor employing enclosure back panel  1  according to the present embodiment. Display section  4  is pivotably attached to main body  5 .  FIG. 2B  is a block diagram of the portable information processor shown in  FIG. 2A . Display device  2  and inputting section  7  are connected with information processing section  6 . Information processing section  6  has such parts as CPU, memory, and hard disk and is built in main body  5 . Inputting section  7  is made up of a keyboard, a touch panel, and a track ball provided on main body  5 , or an interface with external equipment, a media drive, or a mouse connected to information processing section  6  via a cable. Inputting section  7  may be structured of a touch panel disposed on display device  2  of display section  4 . 
     Enclosure back panel  1  of the portable information processor configured as described above is provided thereon with elevated portion  1 A formed by raising a portion of the panel, for enhancing its strength. Top plane  1 C provided on elevated portion  1 A has a concavely curved surface downward from opposed ridge lines  1 B. Therefore, even if an external force is applied to top plane  1 C, tautness of the surface is maintained and the surface strength is secured. Thus, even if enclosure back panel  1  is structured of a thin-walled plate material, its strength against external forces can be secured; namely, enclosure back panel  1  lighter in weight can be obtained. 
     The fabrication method of enclosure back panel  1  will be described with reference to  FIG. 3 .  FIG. 3  is a schematic diagram of a press forming process for fabricating the enclosure back panel according to the present embodiment. First, blank material  14  in a plate form made of a metallic material is fixed as sandwiched between blank holder  16  and die set  13 . Blank material  14  is preferably made of magnesium alloy. Then, blank material  14 , while being heated by heater  15 , is press shaped by punch  12  and thus enclosure back panel  1  is fabricated. 
     Here, die set  13  is provided with convex portion  13 A and punch  12  is provided with concave portion  12 A corresponding to convex portion  13 A. That is, each of punch  12  and die set  13  has a curved structure to form top plane  1 C in a concave shape. Therefore, elevated portion  1 A having top plane  1 C as shown in  FIGS. 1A and 1B  can be formed. 
     When enclosure back panel  1  is fabricated by such a press forming method as described above, there sometimes occurs a material distortion by the press work or a distortion due to a phenomenon that volume of the material becomes more than that of necessity caused by thermal expansion. Even if such a distortion occurs, top plane  1 C is prevented from becoming convex because the excess portion deforms toward the direction in which top plane  1 C becomes more concave. Therefore, top plane  1 C is always stably formed into a concaved shape. Thus, production yield of enclosure back panel  1  is enhanced. 
     In the curved surface of top plane  1 C, it is preferred that mutually opposed two ridge lines  1 D have coaxial cylindrical arc shapes. Thus, by having top plane  1 C formed so as to have a constant curvature, concentration of external forces on a local area can be prevented and, hence, occurrence of deformation of top plane  1 C when subjected to external forces can be lessened. Namely, by forming a stable shape having uniform concavity, the surface strength of enclosure back panel  1  is more enhanced. 
     Although an example of top plane  1 C having such a curved surface that is concaved downward from two ridge lines  1 B is mentioned above, the surface is not limited to that shape. Top plane  1 C may be such that has a curved surface concaved downward from two ridge lines  1 D. It is enough if top plane  1 C has a curved surface concaved downward from one of the two pairs of mutually opposed ridge lines. In either case, it is made possible to obtain a stable shape having small material distortion under press forming work and small waviness on the surface expanded due to thermal expansion. Hence, deformation of top plane  1 C occurring when it is subjected to external forces can be reduced. Also in this case, it is preferred that mutually opposed two ridge lines have coaxial cylindrical arc shapes. In other words, it is preferred that one pair of curved ridge lines of the concavely curved surface have coaxial cylindrical arc shapes. 
     In the present embodiment, an example in which magnesium alloy is used as the material of enclosure back panel  1  is described. Other than that, a thin-walled metallic plate material of aluminum alloy or the like may be used. In view of the strength of the overall enclosure product, however, magnesium alloy is specifically preferred. 
     The above described method may be applied not only to enclosure back panel  1  of enclosure back panel  1  but also to other exterior enclosure members, such as the enclosure back panel of main body  5 . Further, it may be applied to both display section  4  and main body  5 . 
     In the present embodiment, the method of manufacturing enclosure back panel  1  by a press forming method is described. However, the product may be manufactured also by a melt-shaping method. The strength of top plane  1 C in this case can also be enhanced. 
     In the exterior enclosure of portable information processors according to the present invention, the thin-walled material is partly elevated to enhance the strength of the enclosure. Further, it is provided with a stable shape having small material distortion under press forming work and small waviness on the expanded surface due to thermal expansion. Thus, this exterior enclosure is effectively applicable to the display section of portable information processors and the like.