Abstract:
The separation between the light source module for a film scanner and the protection window for pressing against the film document is minimized to increase light intensity by inserting low friction material between the scanning light source module and the protection window. The pressure is exerted by means of a spring or gravity.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to scanners, in particular to scanners for films. 
     (2) Description of the Related Art 
     A scanner for films generally has two modules: the light source module and the optical module. The light source module includes the light source and a carriage for the light source. The optical module is for processing the optical image signal and includes a frame and reflecting mirrors. In conventional scanners for slides, transparencies, photographic film negatives, X-ray films, etc., the light source module and the optical module are two separate entities. The light source module is fixed over the transparent scanning window and the protection window. The optical module is placed underneath the transparent scan window and the protection window. The protection window protects the light source and presses the film document against the scan window. The light source is mounted on the carriage and slides along a rail. The lowest point of the light source module must clear the protection window by a certain distance to allow for structural variations. A typical minimum clearance is 1.5 mm. Because of this 1.5 mm clearance, the light source cannot be in intimate contact with the protection window and the light source intensity is weakened. 
     FIG. 1 shows a prior art optical system of a scanner for films. A light source  10  is mounted on a base  12  which is attached to a carriage  17 . The carriage can slide along a rail  14 . The light source  10  emits a light beam  15  through a protection window  16  which is used to press a film document (not shown) against a scanning window  18 . The light beam transmitted past the scanning window  18  is incident on an optical module  11 , which has mirrors for further processing the optical signals. The base  12  has a light source  10  which is customarily softened with translucent glass placed underneath the base  12 . The light beam emitted from the light source  10  passes through the protective window  16  to scan the film document placed over the scan window  18 . The light beam now contains optical signals for incidence on the first mirror  13  of the optical module  11 . 
     FIG. 2 shows another side view of FIG.  1 . The carriage  17  supports a guide rod  14  on its right side and is attached to a module  12  for housing a light source  10  along its length. The carriage  17  slides along the guide  14 . Underneath the light source module  12  is the protection window  16  and the scan window  18  on which a film document (not shown) is placed. Below the scan window  18  is the optical module  11 . 
     FIG. 9 shows another prior art scanning system for film documents. The carriage  27  also functions as the support for the light source  10 , which is hanging uncovered directly without a housing as shown in FIG. 10, and is capable for sliding along the guide rail  14 . Underneath the protection window  26  is the scan window  18 . The light beam  15  transmits through the protection window  26 , the film document (not shown) and the scan window  18  to reach the optical module  11 . The scan signal is reflected by the mirror  13  for further signal processing. The closest point between the lowest point of the light source  10  and the surface of the protection window  26  is indicated by the distance  284 . 
     Due to manufacturing variations in either the structure of FIG. 1 or FIG. 9, the dimensions of different components may fluctuate somewhat. To allow for such fluctuations, the common practice is to provide a clearance  184  in FIG. 1 and 284 in FIG. 9 of at least 1.5 mm between the lowest point of the light source  10  and the protection window  16  to avoid rubbing the light source  10  against the protection window  16 . 
     SUMMARY OF THE INVENTION 
     An object of this invention is to increase the light intensity of the scanner. Another object of this invention is to place the light source module as close to the optical module as possible. These objects are achieved by pushing the light source module against the optical module by means of spring action or by gravity. Separation between the light source module and the protection window pressing the document to be scanned is minimized to increase light intensity by inserting low friction material between the light source module and the protection window. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 shows the side view of a prior art optical system of a scanner for films. 
     FIG. 2 shows the another side view of the optical system shown in FIG.  1 . 
     FIG. 3 shows an embodiment of the light source module of the present invention. 
     FIG. 4 shows another side view of the light module shown in FIG.  3 . 
     FIG. 5 shows a second embodiment of the present invention. 
     FIG. 6 shows another side view of the structure shown in FIG.  5 . 
     FIG. 7 shows a third embodiment of the present invention. 
     FIG. 8 shows another side view of the structure shown in FIG.  7 . 
     FIG. 9 shows a second prior art optical system. 
     FIG. 10 shows a side view of the structure shown in FIG.  9 . 
     FIG. 11 shows a fourth embodiment of the present invention. 
     FIG. 12 shows another side view of the structure shown in FIG.  11 . 
     FIG. 13 shows a fifth embodiment of the present invention. 
     FIG. 14 shows another side view of the structure shown in FIG,  13 . 
     FIG. 15 shows a sixth embodiment of the present invention. 
     FIG. 16 shows another side view of the structure shown in FIG.  15 . 
     FIG. 17 shows a seventh embodiment of the present invention. 
     FIG. 18 shows another side view of the structure shown in FIG.  17 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 shows the side view of the first embodiment of the present invention. A carriage  37  provides scanning function by sliding along a rail  14 . The light source module  32  houses a light source  10  to provide soft lighting. The protection window  16  protects the light source module  32  and presses against the film (not shown) to be scanned. A spring  20  is used to press the light source module  32 , and is placed between the carriage  37  and the light source module  32 . To allow the light source module  32  to slide over the protection window  16 , two friction coefficient linings  182  are placed under the light source module  32  to reduce the friction between the sliding fight source module  32  and the protection window  16 . 
     FIG. 4 shows another side view of the structure shown in FIG.  3 . The sliding carriage  37  has guide rod  14 . The light source module  32  encloses the one light source  10  to produce soft light. The protection window  16  protects the light source module  32  and presses the film document (not shown) to be scanned. The elastic element  20  such as a spiral spring is placed between the carriage  37  and the light source module  32  to provide elastic coupling between the light source module  32  and the carriage  37 , thus providing smooth sliding action of the light source module  32  over the protection window  16 . The low friction pads  182  along the two sides of the light source module  32  allow the light source module  32  to slide smoothly over the protection window  16 . 
     FIG. 5 shows the side view of a second embodiment of the present invention. A carriage  47  can slide back and forth along a guide rail  14  for scanning. The light source module  42  houses a light source  10  to provide soft lighting. The protection window  16  protects the light source module  42  and presses against the film (not shown) to be scanned. The light module  42  has a T-bar head  422  which is clamped between the claws  472  of the carriage  47 . Thus the light source module  42  is coupled to the lower part of the carriage  47 . The light source module  42  rests on the protection window by gravity and slides freely. The clearance  484  between the bottom of the claw-shape carriage  47  and the top of the T-bar of the light source module  42  allows for fluctuations in the dimensions of the different components of the structure. Two low friction linings  282  are placed under the light source module  42  to reduce friction for the light source module  42  to slide over the protection window  16 . 
     FIG. 6 shows another side view of FIG. 5 The sliding carriage  47  has a guide rod  14 . The light source module  42  encloses a light source  10  to produce soft lighting and is clamped by the carriage  47  by the claws  472 . The protection window  16  protects the light source module  42  and presses the film document (not shown) to be scanned. The weight of the light source module  42  presses against the protection window  16  by gravity. The low friction pads  282  along the two sides of the light source module  42  allow the light source module  42  to slide smoothly over the protection window  16 . 
     FIG. 7 shows a third embodiment of the present invention. The structure is similar to that of FIG. 5 except that the low friction pads  382  are placed over the protection window  16  instead of attaching to the light source module  42 . FIG. 8 shows another side view of FIG.  7 . Note that the low friction pads  382  are placed over the protection window  16 . 
     FIG. 11 shows a fourth embodiment of the present invention. The structure is an improvement over the prior art structure shown in FIG.  9 . The carriage  27  is capable of sliding along a guide rail  14 . The light source  10  is hanging uncovered on a light source plate  22  without being enclosed. The light source plate  22  is coupled to the carriage  27  through a spring  20 . The light source  10  is coated with two rings of low friction layer  482  by means of electrolysis, painting, wrapping, etc. to allow the light source plate  22  to slide smoothly over the protection window  26 . 
     FIG. 12 shows another side view of FIG.  11 . The carriage  27  supports a guide rod  14  on its right side. The light source  10  hangs uncovered under the light source plate  22 . The elastic element  20  placed between the carriage  27  and the light source plate  22  provides smooth sliding action of the light source plate  22  over the protection window  26 . The low friction rings  482  of the light source  10  allow the light source plate  22  to slide smoothly over the protection window  16 . 
     FIG. 13 shows a fifth embodiment of the present invention. The structure is similar to FIG. 11, except that a sidewall  582  is erected at two ends of the light source  10  and is made of low friction material to allow smooth sliding of-the light source plate  22  over the protection window  26 . 
     FIG. 14 shows another side view of FIG.  13 . The carriage  27  supports a guide rod  14  on its right side. The light source  10  hangs bare on the light source plate  22 . The elastic element  20  placed between the carriage  27  and the light source plate  22  provides smooth sliding action of the light source  10  over the protection window  16 . The low friction walls  582  allow the light source plate  22  to slide smoothly over the protection window  16 . 
     FIG. 15 shows a sixth embodiment of the present invention. The difference between FIG.  15  and FIG. 11 is that no elastic spring  20  is used. Instead, a T-bar light source plate  52  is clamped by a carriage  47  to replace the elastic spring. The carriage  47  is capable of sliding along a guide rail  14 . The light source  10  hangs uncovered on the light source plate without being enclosed. The light source plate  22  has a T-bar head  522 , which is clamped between the claws  472  of the carriage  47 . Thus the light source plate  52  is coupled to the lower part of the carriage  47 . The light source  10  rests on the protection window by gravity over the protection window  26 . The light source  10  is wrapped with a layer of low friction rings  482  to allow the light source  10  to slide smoothly over the protection window  16 . 
     FIG. 16 shows another side view of the structure shown in FIG.  15 . The carriage  47  supports a guide rod  14  on its right side. The light source  10  hangs bare on the light source plate  52  and provides a soft lighting. The protection window  16  protects the light source  10  and presses the film document (not shown) to be scanned. The light source plate has a T-bar head  522  which is clamped by the claws  472  of the carriage  47 . The coupling between the T-bar head  522  and the claws  472  renders the light source plate  52  to follow the movement of the carriage  47 . The light source  10  presses the protection window  16  by gravity. The light source is wrapped with low friction material  482  at the two ends to allow the light source  10  to slide smoothly over the protection window  16 . 
     FIG. 17 shows a seventh embodiment of the present invention. The difference between this structure and FIG. 3 is that light source module  32  is supported by four wheels  682  which can roll along the direction of a guide rod  14  and provides low friction to the sliding movement for the light source to slide over the protection window. FIG. 18 shows another side view of FIG. 17 showing the four wheels located at the four corners of the light source module  32 . 
     In conventional scanners, the protection window  15  is typically 2 mm thick. Typical tolerance  184  between the protection window  16  and the lowest point of the light source module is 1.5 mm. In the present invention, the distance between the protection window  16  and the light source module is less than 0.2 mm. The light intensity is inversely proportional to the square of the distance from the light source. The former intensity is 1/(1.5+2) 2 =1/12.25. For the present invention, the intensity is proportional to 1/(0.2+2) 2 =1/4.84. In comparison, the light intensity of the present invention is stronger by a factor of (1/4.84)/(1/12.25)=2.53. It shows that the present invention can fully utilize the available energy. In addition, due to increased light intensity, the exposure time is reduced, and the scanning speed can be increased. In conventional technology, more than one light bulb may be used to increase the light intensity. Reflectors may also be used to increase the light intensity. These techniques may also be incorporated with the present invention. On a one-on-one comparison, the present invention is far superior to the conventional techniques. Besides, the present invention allows the light source module to be in intimate contact with the protection window to avoid any error caused by fluctuation in manufacturing process. 
     The elastic element  20  described in the foregoing paragraphs uses a spiral spring as an example. Other kinds of elastic elements such as C-spring, S-spring, rubber, etc. may also be used. 
     While particular embodiments of the invention have been described, it will apparent to those skilled in the art that various modifications may be made in the embodiments without departing from the spirit of the present invention. Such modifications are all within the scope of this invention.