Abstract:
This invention is related to a backlight module for a liquid crystal display device and, more particularly, to a backlight module having a frame with an impact damping design. The impact damping design can damp impact or absorb impact energy, and thereby protect the important components of the backlight module, such as the lamp or the light guide plate. The backlight module includes a light guide plate that has at least one protrusion located at its periphery, and a frame that has at least one indentation part located at its inner side edge. The indentation part engages with the protrusion to fix the light guide plate, and has at least one opening nearby to damp an impact to the indentation part.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a backlight module for a liquid crystal display device and, more particularly, to a backlight module having a frame with an impact damping design used in a liquid crystal display device. 
     2. Description of Related Art 
     With reference to  FIGS. 1 and 2 ,  FIG. 1  is a top view of the backlight module of a prior art, and  FIG. 2  is an enlarged sectional view taken along the line A—A in  FIG. 1 . The liquid crystal display device commonly needs an additional backlight module acting as a light source. In practice, the backlight module uses a light guide plate  11  to transform the light rays provided by a lamp  12  into a uniform planar light source, and a frame  10  to accommodate and fix all the components of the backlight module. 
     When estimating the reliability of a backlight module, the Shock Test is one of the important tests. Two particular requirements to pass the Shock Test are that the structure of the backlight module cannot be deformed, and the components of the backlight module, such as the light guide plate  11  or the lamp  12  cannot be damaged, the lamp  12  especially. The type of the lamp  12  most used currently in the industry is the cold cathode fluorescent lamp (CCFL), which contains mercury vapor. If the cold cathode fluorescent lamp is damaged, then the user and the environment will be seriously contaminated. Therefore, under the demands of environmental protection and safety consideration, the conditions for carrying out the Shock Test have become more and more exhaustive. In particular, the light guide plate  11  often impacts the lamp  12  due to inertia when external shock energy is applied. Therefore, there must be a suitable design for fixing the light guide plate  11 . 
     However, the design for fixing the light guide plate is confronted by strict challenges, which are illustrated as the following: 
     Firstly, as the information products have a tendency toward being lightweight and small in size, there is less and less space on the frame  10  for constructing a fixing structure. In addition to that, the frame  10  must reserve some space for disposing the cables of the driving ICs because more and more Driving ICs are needed. Consequently, the usable space of the frame  10  is even more reduced. 
     Secondly, the light guide plate  11  has to provide a uniform planar light source. The light-guiding efficiency of the light guide plate  11  and the progress paths of the light rays have been precisely simulated and experimented with. Accordingly, any irregular protrusion or indentation on the light guide plate will cause local light dispersion to be not uniform. 
     Thirdly, the light entry side  13  of the light guide plate  11  easily impacts on the lamp  12  when the Shock Test is carried out. Also, the light entry side  13  is a receiving side that receives the light rays coming from the lamp  12 . Under the consideration of the displaying brightness, there cannot be any blocking structure located between the light guide plate  11  and the lamp  12  to prevent the light guide plate  11  from impacting on the lamp  12 . 
     Japanese Patent No. JA-2003-66420 disclosed a fixing design of a light guide plate, which is relevant to the above-mentioned problems. With reference to  FIG. 3 , there is a lamp housing  22  for locating a lamp (not shown in this figure), and a frame  21  with an indentation part  24 . The light guide plate has a protrusion (not shown in this figure) that corresponds to the indentation part  24  so that the light guide plate can be fixed. Near the indentation part  24 , there is a slit  23  for forming a damping structure  25 . However, such a design will face the problems described below: 
     (I) Too much space is occupied: Said patent utilizes the slit to form a damping structure resembling a cantilever beam, which occupies too much space. Especially, as the information products tend to be light, thin, and small, and more and more driving ICs are required to get higher resolution, there must be space reserved on the frame for disposing the cables. Consequently, difficulties are experienced in applying that design. (II) The root of the cantilever beam is easily broken: Because the root  26  of the cantilever is frail, it will be broken easily when the condition of the Shock Test becomes particularly severe. (III) The test and verification of the fixing design are difficult: Because the result of the Shock Test is unpredictable, the fixing design has to undergo continuous modification and practical verification from design on paper to mass production. However, the mold for producing the frame structure disclosed by that patent is hard to be modified and thus a lot of verification time is needed. (IV) The structure of the mold is complex: No matter whether it is the verification process before making the mold, or the modification process after making the mold, both the structures concerned are complex and both the processes are time-consuming, and thus the exploitation progress is seriously delayed. 
     TW Patent No. 525,791 disclosed another similar design for fixing the light guide plate of the backlight module. With reference to  FIG. 4 , there is an indentation part  34  formed on a frame  31 , and a protrusion  33  located on a light guide plate  32 . The protrusion  33  can engage with the indentation part  34  to fix the light guide plate  32 . In order to pass the Shock Test and prevent the corner  35  of the protrusion  33  from cracking, the corner  35  is commonly designed as a circular angle that can avoid stress concentration. However, based on the consideration of usable space on the frame  31 , the width W of the protrusion  33  is already very small (about 5 mm). If the corner is designed as a circular angle, the straight part  36  of the protrusion  33  will be even smaller. Combined with the manufacturing tolerance, the protrusion  33  of the light guide plate will easily come off the indentation part  34 , and then the light guide plate will impact on the lamp. Hence, the shock durability of that design is still not high enough. 
     Therefore, it is desirable to provide a backlight module with an impact damping design to mitigate and/or obviate the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a backlight module having high durability for successfully undergoing the Shock Test. 
     Another object of the present invention is to provide a backlight module that is easy to be verified. 
     To achieve the object, the backlight module with an impact damping design of the present invention includes a light guide plate that has at least one protrusion located at its periphery, and a frame that has at least one indentation part located at its inner side edge. The indentation part engages with the protrusion to fix the light guide plate, and has at least one opening nearby. The opening and its vicinity form a damping structure that can absorb the impact energy transferred from the protrusion during the Shock Test, and prevent the protrusion from breaking. 
     To achieve the object, another backlight module with an impact damping design of the present invention includes a light guide plate that has at least one indentation part located at its periphery, and a frame that has at least one protrusion located at its inner side edge. The protrusion engages with the indentation part to fix the light guide plate, and has at least one opening nearby. The opening and its vicinity form a damping structure. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section view showing the backlight module of the prior art; 
         FIG. 2  is an enlarged cross-sectional view taken along the line A—A in  FIG. 1 ; 
         FIG. 3  is a perspective view showing the damping structure of the frame in one prior art; 
         FIG. 4  is a top view showing the damping structure of the frame in another prior art; 
         FIG. 5  is a cross-section view showing the backlight module of the present invention; 
         FIG. 6  is a top view showing the damping structure of one preferred embodiment of the present invention; 
         FIG. 7  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 8  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 9  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 10  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 11  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 12  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 13  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 14  is a top view showing the damping structure of another preferred embodiment of the present invention; 
         FIG. 15  is a top view showing the damping structure of another preferred embodiment of the present invention; and 
         FIG. 16  is a top view showing the damping structure of another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIGS. 5 and 6 , the backlight module has a frame  100 , which accommodates a light guide plate  200  and a lamp  300 . The light guide plate  200  has a pair of protrusions  210  located symmetrically at its periphery  220 . The frame  100  has a pair of indentation parts  110  that correspond to the protrusions  210  of the light guide plate  200 . By engaging the indentation parts  110  with the protrusions  210 , the light guide plate  200  is fixed by the frame  100 . The present invention is particularly characterized in that an opening  120  is formed near the indentation parts  110  on the frame  100  and, certainly, between the protrusion  210  and the lamp  300 . The opening  120  can weaken the strength of its nearby structure on the frame  100  and form a damping part  130 . When the protrusion  210  of the light guide plate  200  impacts on the indentation part  110  of the frame  100  due to an impact or a shock caused by the Shock Test or an accident that takes place on the backlight module, the energy of the impact or the shock can be effectively absorbed by the damping part  130 . Therefore, the protrusion  210  is not easily broken, especially the corner  230 . The equivalent in the prior art of the corner  230  used to be easily broken due to the concentrated stress. In order to moderate the concentration of stress, the corner  230  is therefore designed to be a circular angle. The larger the curvature of the circular angle is, the better the moderation of the concentration of stress will be. However, the aforesaid design has some limitations and derivative problems. As the curvature of the circular angle is increased, the straight part  240  of the protrusion  210 , which is used to engage with the straight part  140  of the indentation part  110 , will become shorter and shorter. In addition to that, the deviation caused by manufacturing tolerance should be considered at the same time. As a result, the light guide plate  200  will easily escape the constraint given by the frame  100 , and then impact on the lamp. Nevertheless, the design of the present invention can reduce the curvature of the corner  230 , and even permit the corner  230  to be a right angle. Hence, not only the reliability of the backlight module can be improved, but also the range of manufacturing tolerance that may affect production cost need not to be so tight. Furthermore, the top half edge  250  of the protrusion  210  can be a bevel edge when the backlight module only mounts a lamp below the light guide plate, because no concern need be given about impact on the top lamp and the bevel edge is sufficient for damping the impact and preventing the concentration of stress. 
     Anyone skilled in the art can easily infer that the shape of the opening  120  is not restricted to the rectangle drawn in  FIG. 5 . The opening  120  can be a circle or other polygons. The depth of the opening  120  is not limited, either. The opening  120  can be a through hole or a blind hole. Moreover, the location of the opening  120  is not restricted to be below the protrusion  210  and can also be above the protrusion  210 . Alternatively, a pair of openings  121 ,  122  can be located respectively below the protrusion  211  and above the protrusion  211 , as shown in  FIG. 7 . Similarly, the frame  101  can engage with the protrusion  211  for fixing the light guide plate. Next, with reference to  FIG. 8 , the light guide plate  400  of the backlight module has an indentation part  410  at its periphery, and a protrusion  510  that corresponds to the indentation part  410  is formed at the inner side edge of the frame  500 . Through the engagement between the protrusion  510  and the indentation part  410 , the light guide plate  400  is fixed by the frame  500 . Furthermore, an opening  530  is located near the protrusion  510  to form a damping part  520  with a weakened structure. As in the principle described above, the damping part  520  similarly can absorb the impact energy and thus protect the lamp and the light guide plate  400 . 
       FIG. 9  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 7 . In this damping structure, there are two openings  121 ,  122  located below and above the protrusion  211  of the light guide plate, respectively. Besides, the protrusion  211  of the light guide plate is circular, while the corresponding indentation part of the frame  101  is circular, too. 
       FIG. 10  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 7 . In this damping structure, there are two openings  121 ,  122  located below and above the protrusion  211  of the light guide plate, respectively. Besides, the protrusion  211  of the light guide plate is trapezoid-shaped, while the corresponding indentation part of the frame  101  is trapezoid-shaped, too. 
       FIG. 11  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 7 . In this damping structure, there are two openings  121 ,  122  located below and above the protrusion  211  of the light guide plate, respectively. Besides, the protrusion  211  of the light guide plate is triangular, while the corresponding indentation part of the frame  101  is triangular, too. 
       FIG. 12  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 7 . In this damping structure, there are two openings  121 ,  122  located below and above the protrusion  211  of the light guide plate, respectively. Besides, the protrusion  211  of the light guide plate is polygonal, while the corresponding indentation part of the frame  101  is polygonal, too. 
       FIG. 13  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 8 . In this damping structure, the light guide plate  400  of the backlight module has a triangular indentation part  410  at its periphery, and a triangular protrusion  510  that corresponds to the indentation part  410  is formed at the inner side edge of the frame  500 . Through the engagement between the protrusion  510  and the indentation part  410 , the light guide plate  400  is fixed by the frame  500 . Furthermore, an opening  530  is located near the protrusion  510  to form a damping part  520  with a weakened structure. The damping part  520  absorbs the impact energy and thus protects the lamp and the light guide plate  400 . 
       FIG. 14  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 8 . In this damping structure, the light guide plate  400  of the backlight module has a polygonal indentation part  410  at its periphery, and a polygonal protrusion  510  that corresponds to the indentation part  410  is formed at the inner side edge of the frame  500 . Through the engagement between the protrusion  510  and the indentation part  410 , the light guide plate  400  is fixed by the frame  500 . Furthermore, an opening  530  is located near the protrusion  510  to form a damping part  520  with a weakened structure. The damping part  520  absorbs the impact energy and thus protects the lamp and the light guide plate  400 . 
       FIG. 15  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 8 . In this damping structure, the light guide plate  400  of the backlight module has a circular indentation part  410  at its periphery, and a circular protrusion  510  that corresponds to the indentation part  410  is formed at the inner side edge of the frame  500 . Through the engagement between the protrusion  510  and the indentation part  410 , the light guide plate  400  is fixed by the frame  500 . Furthermore, an opening  530  is located near the protrusion  510  to form a damping part  520  with a weakened structure. The damping part  520  absorbs the impact energy and thus protects the lamp and the light guide plate  400 . 
       FIG. 16  is a top view showing the damping structure of another preferred embodiment of the present invention, which is similar to the damping structure shown in  FIG. 8 . In this damping structure, the light guide plate  400  of the backlight module has a trapezoid-shaped indentation part  410  at its periphery, and a trapezoid-shaped protrusion  510  that corresponds to the indentation part  410  is formed at the inner side edge of the frame  500 . Through the engagement between the protrusion  510  and the indentation part  410 , the light guide plate  400  is fixed by the frame  500 . Furthermore, an opening  530  is located near the protrusion  510  to form a damping part  520  with a weakened structure. The damping part  520  absorbs the impact energy and thus protects the lamp and the light guide plate  400 . 
     Through the comparison between the present invention and the prior arts, it can be summed up that the present invention has the following advantages: 
     1. The damping structure occupies little space of the frame, and hence the frame can offer a sufficient space for other use; 
     2. The damping structure is stable, so it does not fail through damage otherwise easily occurring. Therefore, it can absorb the impact energy effectively, and pass the strict Shock Test. 
     3. Owing to the impact energy absorbing capability of the damping structure, the curvature of the corner at the joint of the protrusion and the light guide plate can be reduced, and the corner can even be a straight angle. Hence, the range of the straight engagement is substantially enlarged. As a result, the light guide plate is successfully prevented from coming off the indentation part as well as preventing impact on the lamp. 
     4. The verification of the design effect is easier than that of the prior arts. Because the damping structure of the present invention is easily manufactured, its effect can be immediately verified by using a handmade sample. Therefore, the bottleneck that used to be encountered at the design process can be resolved right away. 
     5. The mold is easy to be modified. Because only an opening is needed, the process is simpler than the prior arts. Besides, the original whole structure of the mold is not affected, and the modification schedule can be controlled easily. 
     6. The present invention can be carried out easily. Because only the mold is modified and no additional handmade treatment is required, therefore, the present invention does not need more labor hours and is quite suitable for mass production. Thus, the cost of material and manpower will not be increased. 
     7. Not only the impact energy transferred in the vertical direction can be absorbed by the damping structure of the present invention, but also that in the horizontal direction can be absorbed. Consequently, the impact durability and reliability of the backlight module using the damping structure of the present invention is high. 
     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.