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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
   The present invention relates to a latch mechanism, and more particularly to a latch mechanism for a portable computer. 
   DESCRIPTION OF PRIOR ART 
   Typically, an electronic device, such as a portable computer, includes a cover unit and a base unit pivotally connected with the cover unit, and a latch mechanism is provided to lock the cover unit to the base unit. 
   As disclosed in U.S. Pat. No. 6,115,239, a latch mechanism for locking a cover unit to a base unit, includes a latch frame movably installed inside the cover unit, a plurality of latches are formed on the latch frame at predetermined intervals and one end portion of each latch protrudes from a front surface of the cover unit, and a slide knob is operatively connected to the latch frame for concurrently operating the latches. The latches are inserted into and locked by latch grooves formed at positions corresponding to the latches on an upper surface of the base unit. The latches are urged against the base unit by elastic forces applied by double springs mounted on two ends of the latch frame. However, to open the cover unit, the slide knob is slid to overcome the elastic forces of the springs to move the latch mechanism for disengaging from the base unit. The slide force depends on friction between the slide knob and fingers of an operator. It is laborious for an operator to provide enough force to move a slide knob. 
   What is needed, therefore, is a laborsaving latch mechanism. 
   SUMMARY OF THE INVENTION 
   An exemplary latch mechanism is provided for locking a cover unit to a base unit. The latch mechanism includes a latching member for being slidably installed in the cover unit and a button for being rotatably fixed to the cover unit. The latching member includes a main body and a hook extending from the main body for engaging with the base unit. The button includes a driving surface operatively engagable with the main body of the latching member for cooperatively transforming rotating movement of the button into linear movement of the latching member thereby disengaging the hook from the base unit. 
   Other advantages and novel features will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded, isometric, inverted view of a latch mechanism with a cover unit in accordance with a preferred embodiment of the present invention, and the cover unit includes a first panel and a second panel; 
       FIG. 2  is an enlarged, assembled view of  FIG. 1  without the second panel of the cover unit; 
       FIG. 3  is similar to  FIG. 2 , but showing another state of the latch mechanism; and 
       FIG. 4  is a schematic, assembled and partly-sectioned view of  FIG. 1  with a base unit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 4 , a latch mechanism is provided in accordance with a preferred embodiment of the present invention, for locking a cover unit  10  to a base unit  50  of an electronic device, such as a portable computer. The latch mechanism includes a button  20 , a latching member  30 , and an elastic member  40 . In this embodiment, the elastic member  40  is a spring. 
   The cover unit  10  includes a first panel  11 , and a second panel  13  having a pair of through holes  131  defined therein. The first panel  11  includes a front wall  111 , and a recess  112  is defined inward in the middle of the front wall  111 . A pivot  113  extends up from an inside surface of the first panel  11  at the rear of the recess  112 . A first plate  114  and a second plate  115  are formed oppositely on the inside surface of the first panel  11  adjacent the front wall  111 . A first guiding hole  116  is drilled in a generally middle portion of the first plate  114 , and a second guiding hole  117  is defined in the second plate  115  by cutting out a top portion thereof. Two spaced guiding tabs  118  are disposed generally between the first and second plates  114 ,  115  in parallel to the front wall  111 . 
   The button  20  is generally a circular plate with a portion cut out therefrom. A pivot hole  21  is defined through a center of the circular plate. A knob  23  extends from a circumferential surface of the circular plate. A planar blocking surface  24  is formed extending from the circumferential surface to but not reaching the pivot hole  21  of the button  20 , and spaced from the knob  23 . An arcuate mating surface  25  extends a predetermined length around the pivot hole  21  from an end of the blocking surface  24  adjacent the pivot hole  21 . An arcuate driving surface  26  is defined with two ends thereof communicating with the mating surface  25  and the circumferential surface respectively. An acme of the mating surface  25  is nearer to the pivot hole  21  than an acme of the driving surface  26 . 
   The latching member  30  includes a main body  31  with an arcuate middle portion offsetting a distance from a line defined by two opposite ends thereof. An arcuate concave section  312  is defined in the middle portion of the main body  31  communicating with a lateral surface  311  thereof, corresponding to the mating surface  25  of the button  20 . An arcuate recessed section  313  is formed in the middle portion of the main body  31 , and cooperatively forms a protruding edge with the concave section  312 , corresponding to the driving surface  26  of the button  20 . A pair of hooks  32  each having a hooking portion  321  protrude out from a top surface of the main body  31 , corresponding to the through holes  131  of the second panel  13 . A first rod  33  and a second rod  34  extend from the two opposite ends of the main body  31  respectively. 
   Referring particularly to  FIG. 4 , the base unit  50  defines a pair of latching slots  51 , corresponding to the hooks  32  of the latching member  30 . 
   Referring also to  FIGS. 1 and 2 , in assembly, the elastic member  40  is placed around the first rod  33  of the latching member  30 , and a free end of the first rod  33  extends through the first guiding hole  116  of the first plate  114  of the first panel  11 , with two free ends of the elastic member  40  respectively engaging with the main body  31  of the latching member  30  and the first plate  114  of the first panel  11 . The second rod  34  of the latching member  30  is pressed down into the second guiding hole  117  from the top portion of the second plate  115 . Another lateral surface of the main body  31  of the latching member  30  engages with the guiding tabs  118 , thereby slidably fixing the latching member  30  to the first panel  11 . The button  20  is pivotably mounted on the first panel  11  with the pivot  113  of the first panel  11  extending through the pivot hole  21  of the button  20 . The blocking surface  24  of the button  20  abuts against the lateral surface  311  of the main body  31  of the latching member  30 , the mating surface  25  of the button  20  is fittingly engaged with the concave section  312  of the main body  31 , and the driving surface  26  of the button  20  is received in the recessed section  313  of the main body  31 . The knob  23  of the button  20  extends out through one side of the recess  112  of the front wall  111  of the first panel  11 , for being manipulated from outside the first panel  11 . 
   The second panel  13  holds a liquid crystal display therein, and the first panel  11  is fixed to the second panel  13  to secure the liquid crystal display. The hooks  32  of the latching member  30  extend outward from the through holes  131  of the second panel  13  respectively; thereby, the cover unit  10  is fully assembled. The cover unit  10  is then pivotably attached to the base unit  50 . 
   In use, the cover unit  10  is pivoted to cover the base unit  50  when the electronic device is not in use. When bottom surfaces of the hooking portions  321  of the hooks  32  abut against portions adjoining the latching slots  51  of the base unit  50  respectively, the cover unit  10  is pressed downward and the latching member  30  is therefore pushed to compress the elastic member  40  and slides toward the first plate  114  until the hooking portions  321  of the hooks  32  entirely enter the latching slots  51  respectively. After that, the elastic member  40  is restored pushing the latching member  30  to slide toward the second plate  115 , top surfaces of the hooking portions  321  of the hooks  32  engage with the portions of the base unit  50  adjoining the latching slots  51 . Thus, the cover unit  10  is locked to the base unit  50 . 
   Referring further to  FIG. 3 , to unlock the cover unit  10  from the base unit  50 , the knob  21  of the button  20  is pushed from one side to the other side of the recess  112  to rotate the button  20  around the pivot  113 . Concurrently, the blocking surface  24  and the mating surface  25  of the button  20  disengage from the lateral surface  311  and the concave section  312  of the latching member  30  respectively. The driving surface  26  of the button  20  contacts and drives the protruding edge shared by the concave section  312  and the recessed section  313  of the latching member  30 , and the latching member  30  is therefore pushed to slide toward the first plate  114  compressing the elastic member  40 . The button  20  is continually operated to move the latching member  30  until most of the driving surface  26  of the button  20  engages with the recessed section  313  of the latching member  30 , the hooking portions  321  of the hooks  32  move in corresponding latching slots  51  and disengage from the portions adjoining the latching slots  51  respectively, the cover unit  10  is ready to be pivoted open. After the cover unit  10  is opened, the elastic member  40  is restored driving the latching member  30  back, and the latching member  30  drives the button  20  to reversely rotate until the blocking surface  24  of the button  20  abuts against the lateral surface  311  of the latching member  30 . The cover unit  10  is then ready to be closed. 
   It is believed that the present embodiment and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the example hereinbefore described merely being preferred or exemplary embodiment of the invention.

Summary:
A latch mechanism is provided to lock a cover unit to a base unit, which includes a latching member for being slidably installed in the cover unit and a button for being rotatably fixed to the cover unit. The latching member includes a main body and a hook extending from the main body for engaging with the base unit. The button includes a driving surface operatively engagable with the main body of the latching member for cooperatively transforming rotating movement of the button into linear movement of the latching member thereby disengaging the hook from the base unit.