Abstract:
In the scanning optical module of a scanner, the light source module is mounted over the lens module through a spring to push the light source module against the scan window. Thus, the light source is moved closer to the document to be scanned and irradiates the document with higher intensity than prior art light source, which must be clear away from the scan window to allow for manufacturing tolerances.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to a scanner, in particular to the light source of the scanner. 
     (2) Description of the Related Art 
     In the optical system of a scanner, the light source module can be subdivided into a “light source module” and a “lens module”. The light source module refers to the light source components including the light source and the base for supporting the light source. The lens module is to process the light ray with imaging signal including reflecting mirrors and focusing lens, etc. Conventional light source module and lens module are fixed with respect with each other. 
     FIG. 1 shows the top view of a typical optical module. The light  16  is mounted on an L-shaped base  12  by means of two bracelets  18  as shown in FIG. 2, which is the side view of FIG.  1 . The L-shaped base  12  is mounted over the lens module  10 . The light source scans and irradiates document  50  placed over a scan window  20  and produces a reflected light ray to pass through the light slot  14  on the lens module  10 . As shown in FIG. 2, the reflected light ray  22  through the light slot  14  contains image signal and is reflected by the mirror  102  for further signal processing. 
     The L-shaped base  12  has a vertical flange. While the flange can reinforce the base to prevent bending and concentrate the light intensity to prevent scattering, the vertical flange protrudes upward toward the scan window  20  typically to an elevation higher than the brackets  18  as shown in FIG.  2 . Due to manufacturing variations, allowance must be made to tolerate the any variations in the dimensions of the different components in the light source module and the lens module. In a practical design, the highest point in the light source module must clear the bottom of the window  20  by 3 mm. Otherwise, when the optical module scans the document back and forth, the top of the L-shaped base  12  may scratch the bottom of the scan window and the optical module may even be blocked. As shown in FIG. 2, the distance  66  is the minimum distance of 3 mm allowed for variations in mechanical dimensions of the different components. In practical scanners, the 3 mm allowance is barely enough to prevent scratching. 
     Such an allowance is not desirable, because the light source  16  must be moved away from the scanned document and is weakened as it irradiates the document. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to irradiate the scanned document with a more intense light. Another object of this invention is to move the light source closer to the document being scanned. Still another object of the present invention is to provide smoother scanning motion for the optical module. 
     These objects are achieved by mounting the light source module over the lens module through a spring. The spring pushes the light source module against scan window with minimum clearance. Thus, the light source is moved closer to the document being scanned and the intensity is increased. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 shows the top view of a prior art light source module. 
     FIG. 2 shows side view of FIG.  1 . 
     FIG. 3 shows the side view of a first embodiment of the present invention. 
     FIG. 4 shows an enlarged view of FIG.  3 . 
     FIG. 5 shows the side view of a second embodiment of the present invention. 
     FIG. 6 shows the side view of a third embodiment of the present invention. 
     FIG. 7 shows the side view of a fourth embodiment of the present invention. 
     FIG. 8 shows the side view of a fifth embodiment of the present invention. 
     FIG. 9 shows the end view of FIG.  8 . 
     FIG. 10 shows the side view of a sixth embodiment of the present invention. 
     FIG. 11 shows a first design of the sliding guide for the light source. 
     FIG. 12 shows a second design of the sliding guide for the light source. 
     FIG. 13 shows a third design of the sliding guide for the light source. 
     FIG. 14 shows the end view of FIG.  13 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 shows the side view of the first embodiment of the present invention. The light source  16  is held by the brackets  38 , which are mounted on an L-shaped base  12 . The upper tip of the vertical flange of the L-shaped base is lower than the upper tips of the brackets  38 . The L-shaped base is coupled to the optical module  10  through a spring  30 , which pushes the tips of the brackets  38  against the bottom of the scan window  20 , over which a document  50  to be scanned is placed. The bottom of the base  12  and the top of the lens module  10  is separated by a distance  68 . Due to intimate contact between the brackets  38  and the scan window  20 , the distance between the light source  16  and the document  50  is made much shorter than the prior art shown in FIG.  1 . Without allowing for manufacturing tolerance, the light source  16  irradiates the document with much higher intensity than the prior art. 
     FIG. 4 shows an enlarged view of the L-shaped base  12  and the spring  30 . To provide smooth gliding motion of the light source module under the scan window  20 , the brackets  38  can be made of low friction material such as nylon. 
     FIG. 5 shows a second embodiment of the present invention. The structure is similar to FIG. 4 with same reference numbers referring to the same corresponding parts. The exception is that only the top  382  of the brackets  38  is composed of low friction material. The lower section of the brackets  38  need not be of low friction material. 
     FIG. 6 shows a third embodiment of the present invention. The brackets  68  for holding the light source  16  are of inverted U-shape. The tops  682  of the brackets  68  are in contact with the bottom of the scan window  20 . The brackets  68  are made of low friction material to allow smooth gliding motion of the light source  16  under the scan window  20 . The light source  16  is held by the brackets  68  and mounted on the L-shaped base  12 , which is pushed by a spring  30  as described before. 
     FIG. 7 shows a fourth embodiment of the present invention. The structure is similar to FIG. 6 with same reference numerals referring to the same corresponding parts. The exception is that the inverted U-shaped brackets  68  is capped with a low friction layer  782 , and the body of the brackets  68  itself need not of low friction material. The low friction cap allows smooth gliding motion of the light source under the scan window  20 . 
     FIG. 8 shows a fifth embodiment of the present invention. Two tracks  182  of low friction material are attached under the scan window  20 . These tracks are aligned with the brackets  18  for holding the light source  16 . The brackets  18  are similar to those described in FIG.  2  and mounted on an L-shaped base  12 , which is pushed by springs  30  against the lens module  10 . The low friction tracks allows smooth scanning motion of the light source  16 , while maintaining a short distance between the light source and the scan window  20 . 
     FIG. 9 shows the side view of FIG.  8 . Note the long strip  182  attached under the scan window  20 . 
     FIG. 10 shows a sixth embodiment of the present invention. This structure combines the features of FIG.  8  and FIG.  6 . The brackets  68  have an inverted U-shape and glide under two long tracks  182  under the scan window  20 . Here the brackets  68  need not be of low friction material since the tracks  182  provide the smoothing scan of the light source  16 . The slight source module base  12  on which the brackets  68  are mounted is pushed by the spring to glide smoothly under the scan window  20 . 
     FIG. 11 shows a design of the brackets  78  for holding the light source. The brackets are of U-shape each with two flanges. Each flange is pushed upward by a spring  30 . 
     FIG. 12 shows a second design of the brackets  88  for holding the light source. The brackets are of U-shape with a cover  88  wider than the U-shaped groove forming two flanges. The two flanges are pushed upward by two springs  30 . 
     FIG. 13 shows a third design of the brackets  98 . The brackets  98  are coated directly on the light source  16  and attached to the base  12  of the light source module, which is pushed upward by a spring  30 . The coating may be applied by painting, electrolysis or wrapping. 
     FIG. 14 shows the end view of FIG.  13 . The distance between the light source  16  and the window  20  is the thickness of the coating  98 . 
     In prior art, a typical window  20  has a thickness of 3 mm. A typical allowance  66  between the top of light source module and the scan window  20  is 3 mm. In this present invention, the distance between the top of the light source module and the scan window  20  is less than 0.2 mm. The light intensity is inversely proportional to the square of the distance between the light source and the object. In the former case, the intensity is proportional to 1/(3+3) 2 ={fraction (1/36)}, while in the latter case the light intensity is proportional to 1/(3+0.2) 2 ={fraction (1/10.24)} The light intensity for the present invention is therefore ({fraction (1/10.24)})/({fraction (1/36)})=3.52 times stronger than prior art. Thus, the present intensity ally utilizes the light source. Due to increased intensity the exposure time can be reduced and the scan speed can be increased. Besides, due the intimate contact between the light source module and scan window, the structure can tolerate a large variation in the dimensions of the different components in the light source module. The low friction contact material allows smooth scanning mother of the light source module. 
     While a spiral spring  30  is shown in the foregoing figures, other kinds of springs such as elastic belts may also be used, so long as they can exert a push-up action from the lens module to the light source module. 
     While particular embodiments of the invention have been described, it will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the present invention. Such modifications are all within the scope of this invention.