Abstract:
A backlight device with an easily replaced lamp. The backlight device includes a frame, a lighting guide and at least one lamp assembly. The frame has an inner surface. The lighting guide is disposed inside the frame. The lamp assembly is disposed inside the frame and besides the lighting guide. A gap is provided between the inner surface of the frame and the lamp assembly to decrease the friction applied onto the lamp assembly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a backlight device, wherein it is easy to replace the tubular lamps of the backlight device. 
     2. Description of the Related Art 
     Backlight devices are widely used in liquid crystal displays (LCDs) and scanners. A backlight device has tubular lamps inside to generate light. The lamps need to be replaced when they burn out. U.S. Pat. No. 5,537,296 discloses a structure of a backlight device, the only one part that the backlight device of the burned liquid crystal displays need to replaced is the tubular lamp. Other elements besides the burned lamp are left without being replaced together. However, it is difficult for an operator to disassemble and assemble the backlight device for repairing the burned lamp. JP patent No. 4-104486 and 4-288526 simplify the structure of the backlight device for easy maintenance, wherein the burned lamp is drawn out from the side surface of the backlight device. However, when the friction applied to the lamp is great, it is difficult to draw out a tight tubular lamp. 
     FIG. 1A is an exploded perspective diagram of a conventional backlight device, wherein the directions of top, bottom, left, right, front and rear are defined for easy description. The backlight device includes a first frame  1 , a diffuser  2 , a lighting guide  3 , a reflection sheet  4 , a second frame  5 , a back plate  6  and two lamp assemblies  7 . In the assembling operation, the back plate  6  and the second frame  5  are screwed together via screws  61 , and it looks like a box without a cover. Then, the reflection sheet  4 , lighting guide  3  and diffuser  2  are put in the box in sequence, with one laid over another. Grooves  51  are formed between the second frame  5  and the lighting guide  3 . The lamp assemblies  7  are inserted, from the right to the left, into the grooves  51 . Then, the second frame  5  is engaged with the first frame  1  by the engaging portions  52  to fix all of the elements  4 ,  3 ,  2 ,  7  therebetween. 
     Referring to FIG.  1 B and FIG. 2, each lamp assembly  7  includes two fluorescent tubes  72 , a tube guard  71  covering the fluorescent tubes  72 , and a base  73  for fixing the fluorescent tubes  72  in the tube guard  71 . Light is emitted from the fluorescent tubes  72  to propagate in the lighting guide  3  in two paths: (1) Light  75  passes through the front surface of the lighting guide  3  and then propagates out from the diffuser  2 . (2) Light  76  passes through the rear surface of the lighting guide  3 , is scattered by protrusions  31  on the lighting guide  3 , is reflected by the reflection sheet  4  back to the lighting guide  3 , and then propagates out from the diffuser  2 . The protrusions  31  on the rear surface of the lighting guide  3  are used for scattering the light  76 . The diffuser  2  is provided to further scatter the light  76  so that the distribution of the light  76  out from the diffuser  2  is more uniform (without the diffuser  2 , the images of the protrusions  31  can still be observed by the user in front of the lighting guide  3 ). 
     It is important that the distance between the fluorescent tubes  72  and the lighting guide  3  must be accurately kept, otherwise (a) the light emitted out from the upper portion and lower portion of the lighting guide  3  will be too strong due to the fluorescent tubes  72  are too close to the lighting guide  3 . (b)On the other hand, the light emitted out from the upper portion and lower portion of the lighting guide  3  will be poor due to the fluorescent tubes  72  are far away from the lighting guide  3 . 
     FIG. 3 is a front view of FIG. 1A, wherein the lighting guide  3 , the reflection sheet  4 , the second frame  5  and the back plate  6  are already assembled. Also, the diffuser  2  and the first frame  1  are not shown in FIG.  3 . In assembling operation, the lamp assemblies  7  are inserted into grooves  51  from the right to the left, wherein the grooves  51  is formed and disposed between the second frame  5  and the lighting guide  3 . In the disassembling operation, ordinary the lamp assemblies  7  are pulled out from the grooves  51  from the left to the right. The widths of the grooves  51  and those of the lamp assemblies  7  are well matched to keep the lamp assemblies  7  tight, therefore, it is difficult for an operator to assemble/disassemble the backlight device due to a great friction between the lamp assemblies  7  and the grooves  51 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a backlight device with easy maintained tubular lamps. 
     The backlight device of the present invention includes a frame, alighting guide and at least one lamp assembly. The frame has an inner surface. The lighting guide is disposed inside the frame. The lamp assembly is disposed inside the frame and beside the lighting guide. A gap is provided between the inner surface of the frame and the lamp assembly to decrease the friction between the lamp assembly and the frame, thereby facilitating the replacement of the tubular lamp. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
     FIG. 1A is an exploded perspective diagram of a conventional backlight device; 
     FIG. 1B is a local enlarged view of FIG.1A; 
     FIG. 2 depicts the operation of a conventional backlight device; 
     FIG. 3 is a front view of FIG. 1A; 
     FIG. 4A is a front view of the backlight device in accordance with the present invention; 
     FIG. 4B is a local enlarged view of FIG. 4A; 
     FIG. 4C is a perspective diagram of a second frame of FIG. 4B; 
     FIG. 4D depicts another example of the second frame; 
     FIG. 4E depicts another example of the second frame; 
     FIG. 5 depicts the lamp assembly and the back plate screwed together by a screw. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 4A, grooves  51  are formed and disposed between the lighting guide  3  and the inner surfaces of the second frame  5 . Each groove  51  has a closed end  56  and an open end  57 . 
     FIG. 4B is a local enlarged view of FIG. 4A, wherein the second frame  5  has a first inner surface  59  parallel to the lamp assembly  7  and a second inner surface  53  inclined with respect to the lamp assembly  7 . The lamp assembly  7  meets the inclined inner surface  53  of the second frame  5  at an angle θ, thereby producing a gap therebetween. This arrangement effectively decreases the friction between the lamp assembly  7  and the second frame  5  and facilitates the assembling/disassembling operations. FIG. 4C is a perspective diagram of the second frame  5  of FIG.  4 B. 
     FIG. 4D depicts another example of the second frame  5 , wherein reference numeral  54  indicates an inclined surface to create a gap between the lamp assembly and the second frame. 
     FIG. 4E depicts another example of the second frame  5 , wherein the second frame  5  has a flange  55  on its inner surface  58 . The flange  55  is parallel to the lamp assembly  7 . The inner surface  58  is also parallel to the lamp assembly  7 . The flange  55  creates a gap between the lamp assembly  7  and the inner surface  58  of the second frame  5 , when the flange  55  physically contacts the lamp assembly  7 . 
     Referring back to FIG. 4B, it is understood that the distance D 1  between the first inner surface  59  and the lighting guide  3  is smaller than the distance D 2  between the second inner surface  53  and the lighting guide  3 . 
     The lamp assembly  7  is elongated and has a first end  77 , a second end  78 , a first side surface  79  and a second side surface  80 . Referring to FIG. 5, the first side surface  79  is the top surface of the tube guard  71 . Also, the second side surface  80  is the bottom surface of the base  73 . The width D of the lamp assembly  7  is substantially same as the distance D 1  between the first inner surface  59  and the lighting guide  3 . Therefore, the width D of the lamp assembly  7  is smaller than the distance D 2  (&gt;D 1 ). When the lamp assembly  7  is inserted in the groove  51 , the first side surface  79  physically contacts the first inner surface  59  of the second frame  5  and the second side surface  80  contacts the lighting guide  3 . Also, the first side surface  79  does not contact the second inner surface  53  of the second frame  5  because a gap is provided between the second inner surface  53  and the lamp assembly  7 . Therefore, the friction applied onto the second end  78  of the lamp assembly  7  is smaller than the friction applied onto the first end  77 . That facilitates the insertion of the lamp assembly  7  into the groove  51 . 
     However, the gap formed and disposed between the second inner surface  53  and the lamp assembly  7  makes the second end  78  of the lamp assembly  7  flexible in the groove  51 . In other words, it fails to keep the second end  78  of the lamp assembly  7  at the designed position. Then, the quality of the light emitted from the backlight device is poor. That should be avoided. Therefore, a hole  64  is provided on the back plate  6 , near the end  57  of the groove  51 . A screw  62  goes through the hole  64  to fasten the second end  78  of the lamp assembly  7 . Thus, the second end  78  of the lamp assembly  7  cannot move in the groove  51 . Thus the lamp assembly  7  is substantially parallel to the lighting guide  3 , and the quality of the liquid crystal display is good. 
     In conclusion, the present invention provides a gap between the lamp assembly  7  and the second frame  5  to decrease the friction therebetween. Then, it is easy for a operator to assemble/disassemble the lamp assembly  7 . Furthermore, the lamp assembly  7  is fixed to the back plate  6  at its end  78 . This prevents the second end  78  of the lamp assembly  7  from moving in the groove  51 . Then, the lamp assembly  7  is substantially parallel to the lighting guide  3 , and the quality of the liquid crystal display is good. 
     While the. invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.