Abstract:
A multiple-background device for a scanner and a calibration device utilizing the same principle are disclosed. The multiple-background device includes a shaft, a low-reflectance portion and a high-reflectance portion are formed along the length of the shaft. Thereby the shaft can provide various background colors, and the optical module can acquire a plurality of scan lines by means of rotating the shaft for image calibration.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a device for alternating scan backgrounds and for facilitating the shading correction of a scanner. In particular, the device provides more than one background color and is capable to alternate the background colors of the scanner. Such, The device provides an optical module of the scanner with scan lines of different shades to adjust the shade value of the optical module. 
   2. Description of the Prior Art 
   Conventionally, a flatbed scanner comprises a mobile optical module which move linearly for scanning. When the scanning is in process, the moving optical module captures optical signals of a plurality of scan lines of an original document. An optical sensor of the optical module then produces a scan image based on the acquired scan information. 
   For an original document with binder holes or lacerations, black image emerge on its scan image at the positions corresponding to the binder holes or the edges of the scan image if the scanner has a black scan background. To solve this problem, the state of the art utilizes a white scan background. 
   Another solution for the aforementioned problem is to design a dual scan background including a black scans background and a white scan background. The optical module is driven to move to a position underneath the selected background color and capture image information when the moving original document passes over the optical module. However, since a moveable optical module is required for the transformation of background, this solution is only applicable to a flatbed scanner in combination with a document feeder, as claimed in U.S. Pat. No. 6,166,394. The solution disclosed in said US patent requires the position adjustment of the optical module in accordance with the positions of the background and, thus, makes the positioning of the optical module difficult. 
   A flatbed scanner is applicable for itself or combines with a sheet feeder with an optical module for duplex scanning. However, for a scanner with dual optical modules, the optical modules of the scanner are fixed during the scanning process. If the optical module position corresponding to different background colors changes when performing shading correction, the angles and distances between the optical modules and the original document will be different from those during the scanning process; in result, the scan image using the correction values is defected. Therefore, to ensure best image quality while implementing the background alternation, the best way is not to move the optical module in order not to altering the optical path of the signals which carry the image information. 
   In addition, with the conventional device, the fixed optical module is not capable of capturing a plurality of scan lines, so the result of this shading correction is questionable. According to U.S. Pat. No. 6,323,933, the optical module on top of the scanner body is capable of capturing a plurality of scan lines of a calibration sheet on the optical module moving underneath the scanner. However, the said patent does not solve the problem that the distance between the upper and the lower optical modules may be different from the distance between the original document and the upper optical module. As a result, the optical path length may be different in the two circumstances and, thus, the accuracy of the shading correction is affected. 
   SUMMARY OF THE INVENTION 
   The primary objective of the present invention is to provide a multiple-background device for a scanner, in particular a device providing background color alternation function to solve the problem of the black image due to holes or lacerations on an original document. 
   Another objective of the present invention is to provide a shading correction device for a scanner to capture a plurality of scan lines from the multiple-background device for the shading correction of an optical module. 
   To achieve the aforementioned objectives, a rotating shaft is installed on the scanner of the present invention opposite to the scan window and the optical module of the scanner. The rotating shaft comprises a low reflectivity area and a high reflectivity area. When an alternation of the background colors is required, the rotating shaft is rotated such that the surface area of a selected reflectance is facing the scan window. When a shading correction is required, the rotating shaft only needs to comprise a reflecting area and rotate by one circle so that the optical module can capture a plurality of scan lines for the shading correction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view showing the present invention; 
       FIG. 2  is an outer view showing a rotating shaft of the multiple-background device of the present invention; 
       FIG. 3  is a schematic view showing a usage of the dark background color of the present invention; 
       FIG. 4  is a schematic view showing a usage of the light background color of the present invention; 
       FIG. 5  is a schematic view showing a usage of the present invention for the shading correction; 
       FIG. 6  is a schematic view showing another structure of the multiple-background device of the present invention; 
       FIG. 7  is a schematic view showing a usage of the multiple-background device of the present invention with another structure; 
       FIG. 8  is a schematic view showing an application of the present invention on a sheet fed scanner; and 
       FIG. 9  is an outer view showing another rotating shaft of the multiple-background device of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The embodiment in  FIG. 1  shows a scanner  1  with document feeding function as a combination of an automatic document feeder  10  and a flatbed scanner  30 . The scanner  1  is capable of duplex scanning. The automatic document feeder (ADF)  10  has a fixed optical module  12  that does not move along with scanning movement. The ADF  10  has a scan window  14  on the bottom thereof and the light emitted from a light source  16  can reach to the scan window  14 . Two multiple-background devices  20 ,  50  are disposed in the scanner  1  and opposite to the optical modules  12 ,  34  respectively. The multiple-background device  20 , for example, is disposed in the flatbed scanner  30  and opposite to the scan window  14 . As  FIG. 2  shows, the multiple-background  20  has a rotating shaft  22 , which has a low reflectivity area  24  and a high reflectivity area  26  on the surface thereof. The low reflectivity area  24  may have a black color and high reflectivity area  26  may have a white color. It is important to note that the present invention is not limited to a structure with two reflecting areas on the rotating shaft  22  and more than two reflecting areas are allowable if required. The surface area of the low reflectivity area  24  can be set smaller than the surface area of the high reflectivity area  26 . 
   As shown in  FIG. 3 , the optical module  12 , for example, has a light source  16 , a reflecting mirror  15 , a lens  17 , and an optical sensor  18 . The light source  16  provides light required for scanning, while the reflecting mirror  15  is used to reflect an optical signal  19 . The lens  17  and optical sensor  18  are assembled on the optical path of the optical signal  19 , so that the optical signal  19  is reflected by the reflecting mirror  17  and focused by the lens  17 , and used for producing images when received by the optical sensor  18 . The optical sensor  18  is either a charge coupled device (CCD) or a contact image sensor (CIS). The other optical module  34  may have the same components and configuration as the optical module  12 . 
   As  FIG. 1  shows, the rotating shaft  22  is driven by a power source  62 , which can be either a stepper motor or a servomotor. The power source  62  is also applicable as a power source for the optical module  34 . A solenoid valve can be used as the power source as well to drive the rotating shaft  22  to do reciprocating motions at a specific angle to provide different scanning backgrounds for the optical module  12 . 
   The flatbed scanner  30  has a housing  32  and an optical module  34  capable of doing reciprocating motions. A small scan window  36  and a large scan window  38  are disposed on the surface of the housing  32 . When the flatbed scanner  30  and the ADF  10  are combined, the optical module  34  is fixed to a scanning position and the light emitted from the light source  39  reaches to the small scan window  36 . The multiple-background device  50  disposed in the ADF  10  is located opposite to the optical module  34 . The multiple-background device  50  operates under the same principle as the multiple-background  20 , except that the power source which drives the roller set of the ADF  10  is also applicable as the power source  64  for the multiple-background device  50 . 
   For the multiple-background device  20 , for example, when the high reflectivity area  26  on the surface of the rotating shaft  22  is facing the scan window  14  and an original document  40  passes through the feeding path  42  of the scanner  1 , the background of the document  40  displays a light color. 
   As  FIG. 3 , when a dark background is required, the user may use controls (such as control keys or programmable options of the software used) to rotate the rotating shaft  22  so that the low reflectivity area  24  is facing the scan window  14 . The background color can be changed under the same principle when a light background is required. 
   In addition to providing different background colors, the multiple-background device  20  is applicable as a shading correction device. The shading correction of prior art is carried out by moving an optical module and having a light source illuminating a white calibration strip to capture scan lines. As  FIG. 4  shows, the high reflectivity area  26  is facing the light source  16  by having the rotating shaft  22  of the present invention rotate so that the light source  16  illuminates the high reflectivity area  26 . As  FIG. 5  shows, the light source  16  illuminates different locations of the high reflectivity area  26  when the rotating shaft  22  is rotating. The rotating shaft  22  stops rotating when the low reflectivity area  24  on the rotating shaft  22  is facing the scan window  14 . In doing so, the optical module  12  captures a plurality of scan lines from the high reflectivity area  26  and uses the scan lines for the shading. 
   In the aforementioned embodiment, the rotating shafts  22 ,  52  of the multiple-background devices  20 ,  50  are cylindrically shaped as shown in  FIG. 2 . Another embodiment in  FIG. 6  has a prism as the rotating shaft  23 . A surface area of the prism is designed as a low reflectivity area  25 , while the rest of the surface areas of the prism are designed as a low reflectivity area  27 . More reflecting areas with different colors are allowed by making use of the multiple surface areas of the prism. 
   For the multiple-background device  20  opposite to the optical module  12 , for example as illustrated in  FIG. 7 , the rotating shaft  23  is operated and driven under the same principle as the aforementioned embodiment of the present invention. When the rotating shaft  23  is installed at the same position as the rotating shaft  22  in  FIG. 5  and driven by a power source, the scan background is alternated accordingly. When the rotating shaft  23  is used as a shading correction device for the optical module  12 , the rotating shaft  23  rotates to allow the high reflectivity area  27  facing the light source  16  in order for the optical module  12  to capture a plurality of scan lines for the shading correction. A cross-section of the rotating shaft  23  in  FIGS. 6 and 7  shaped as a polygon will be sufficient for the present invention. 
     FIG. 8  shows the application of the present invention on a sheet fed scanner  2 . The sheet fed scanner  2  has a duplex scanning function and comprises an upper optical module  82  and a lower optical module  84  and corresponding optical modules  82  and  84 . The multiple-background device  72  is located opposite to the optical module  84 , while the other multiple-background device  74  is opposite to the optical module  82 . The sheet fed scanner  2  has two power sources  92  and  94  to drive the multiple-background devices  72  and  74 , respectively, under the same principle as the aforementioned embodiments. The power source  92  or  94  is applicable as the power source of the feeding roller. Since the optical modules of the sheet fed scanner are fixed, the design of the present invention can effectively solve the problems of background alternation and shading correction that prior art sheet fed scanners have encountered. 
   The rotating shaft of the present invention has multiple background colors on the surface thereon and, thus, is capable of changing background colors for scanning. The rotating shaft rotates in a manner of relative motion to the light source and allows the optical module to capture a plurality of scan lines for the shading correction. It is important to note that different background colors result in different amount of light received by the image sensor so that the scan background information transmitted to the optical module is different. 
   In other words, the present invention is designed to display the scan background color by mapping the light and optical signal received by the optical module. As  FIG. 9  shows, a trough  29  is axially formed on the rotating shaft  28 . As the light source illuminates the trough  29 , where an area equivalent to a dark surface is formed, less amount of the light reaches the optical module than when the light source illuminates the area with the trough  29 . Paints of different colors, papers of different colors, or materials of different reflectivities for the reflecting areas on the rotating shaft could achieve the objective of the present invention. In other words, rotating shafts comprising reflecting areas of various reflection coefficients are applicable to the present invention. 
   The aforementioned embodiments are applicable to the dual optical module of a combination of an automatic document feeder and a flatbed scanner, a dual optical module of the sheet fed scanner  2 , and, especially, to a scanner having only one single optical module. Use of the present invention does not affect the background transformation functionality and shading correction accuracy of the multiple-background device. 
   The rotating shafts in the aforementioned embodiments can merely contain a single standard color of a single light reflection coefficient for the shading correction. In other words, if the rotating shaft of the present invention has only a surface area of one light reflection coefficient, it can be used for the shading correction. If the rotating shaft has more than two reflecting areas of various reflection coefficients, it can be used for backgrounds alternation and selectively provides the shading correction functions. 
   Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments that will be apparent to persons skilled in the art. This invention is, there, to be limited only as indicated by the scope of the appended claim.