Abstract:
A scanner capable of selecting scanning positions includes a scanning window, a scanning module and a control processing unit. Before a sheet of documents is scanned, the control processing unit moves the scanning module to a first location to generate a first image datum, and moves the scanning module to a second location to generate a second image datum. The control processing unit compares both the image data according to differences between the first and second image data, and moves the scanning module to a scanning location for scanning the sheet of document.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a scanner and a scanning method for the scanner, and more particularly, to a scanner capable of selecting scanning positions and a scanning method for the scanner for preventing dust grains from affecting scanned images and for improving a scanning quality of the scanner. 
     2. Description of the Prior Art 
     Scanners are primary document processing devices in modern societies, particularly sheet-fed scanners, which are popular for scanning stacks of documents. Differing from the sheet-fed scanner, the flatbed scanner can merely scan one sheet of document in each scan, and it indicates a fact that after a first sheet of document is scanned, a second sheet of document cannot be scanned until the first sheet is removed or replaced, so that the flatbed scanner is troublesome in scanning a large number of documents. On the contrary, the sheet-fed scanner provides an automatic sheet-feeding mechanism, with which the sheet-fed scanner conveys a stack of sheets of documents one by one to a scanning position automatically and scans the stack of sheets consecutively. Therefore, the sheet-fed scanner is easy for usage, and saves much time of users. 
     However, for a sheet-fed scanner, or even for a flatbed equipped with an automatic document feeder, an interior scanning module is fixed at a same location for scanning documents. Therefore, when being scanned, sheets of documents are fed into the scanner one by one by the sheet feeder, and each sheet of document is moved across a scanning window, which is located corresponding to the scanning position of the scanning module. However, when such a scanner has dust grains on the scanning window, the dust grains are scanned along with the documents so that image data generated have unexpected lines, which do not exist on said documents. That is, the scanning quality of the scanner is affected by the dust grains. 
     Though decreasing the amount of dust grains around the scanner may reduce the effect of the dust grains, however, some tiny materials such as tiny dust grains, flakes, or hairs are hard to be removed and avoided. It is more troublesome when such tiny materials adhere to the under side of the scanning window. Moreover, the cleaner the surroundings for the manufacturing of the scanner are, the cost for the production of the scanner gets higher, and a scanner having a higher resolution requires cleaner surroundings. Instead of spending such a huge cost in cleaning surroundings for the manufacturing of the scanner, the scanning mechanism of the scanner is more worthy of being improved for refining the scanning quality. 
     Please refer to  FIG. 1 , which is a simplified diagram of a conventional sheet-fed scanner  100 . The sheet-fed scanner  100  includes a housing  110 , a sheet-in tray  115 , a sheet-out tray  116 , a stepper motor  130 , a roller  125 , a transparent platform  135 , a light source  140 , a memory  150 , a control circuit  155 , and a scanning module  145 . 
     The sheet-in tray  115  is connected to the housing  110  for storing a stack of to-be-scanned documents  120 . The sheet-out tray  116  is also connected to the housing  110  for storing a stack of scanned documents  121 . The stepper motor  130  is disposed interior to the housing  110  for rotating the roller  125  to move the to-be-scanned documents  120  into the housing  110  one by one. The control circuit  155  is utilized for manipulating the scanner  100 . The scanning module  145  is disposed interior to the scanner  100  for scanning the to-be-scanned documents  120  to generate image data of said to-be-scanned documents  120 . The light source  140  provides light required in scans. The memory  150  is utilized for storing the generated image data. The scanning module  145  is located at a scanning position. When the roller  125  moves a sheet of the to-be-scanned documents  120  across the scanning position, the scanning module  145  scans the sheet of the to-be-scanned documents  120 , and stores an image datum generated by scanning the sheet of the to-be-scanned documents  120  into the memory  150 . 
     The scan procedure implemented on the sheet-fed scanner  100  includes steps as follows: 
     Step  00 : Load the to-be-scanned documents  120  in the sheet-in tray  115  of the sheet-fed scanner  100 . 
     Step  05 : Initiate the scan procedure for the to-be-scanned documents  120 . 
     Step  10 : Control the stepper motor  130  to rotate the roller  125  for moving sheets of the to-be-scanned documents  120  to the transparent platform  135 . 
     Step  15 : Control the scanning module  145  with the control circuit  155  to scan sheets of the to-be-scanned documents  120  when the roller  125  moves the to-be-scanned documents  120  sheet by sheet across the scanning position, and store image data of the to-be-scanned documents  120  into the memory  150 . 
     Step  20 : Repeat Step  10  and Step  15  until all sheets of the to-be-scanned documents  120  are scanned. 
     In the scan procedure, the scanning module  145  scans the to-be-scanned documents  120  sheet by sheet at a same location, i.e., the scanning position of the scanning module  145  for scanning the to-be-scanned documents  120  is fixed. Therefore, when there are dust grains  180  at the scanning position of the scanning module  145  on the transparent platform  135 , there are corresponding lines on the generated image data. 
     Please refer to  FIG. 2 , which is a diagram of an image datum  220  when there is a dust grain  180  at the under side of the transparent platform  135  of the sheet-fed scanner  100 . As illustrated in  FIG. 2 , there is a line  280  on the image datum  220 . The line  280  results from the fact that when a sheet of the to-be-scanned document  120  is moved across the transparent platform  135 , the dust grain  180  keeps on preventing lights from passing through and results in a corresponding shadow in the scan. If the dust grain  180  is removed at the scanning position, the line  280  disappears too. Therefore, the scanning quality of the sheet-fed scanner  100  is severely affected by the dust grain  180  adhering to the transparent platform  135 . 
     SUMMARY OF THE INVENTION 
     The claimed invention discloses a scanning method for a scanner capable of selecting scanning positions. The scanning method comprises moving a scanning module to a first position to generate a first image datum, moving the scanning module to a second position to generate a second image datum, comparing the first image datum with the second image datum for calculating a difference between the first image datum and the second image datum, and scanning a document with the scanning module according to the calculated difference between the first image datum and the second image datum. 
     The claimed invention also discloses a scanner capable of selecting scanning positions. The scanner comprises a housing, a scanning window disposed on the housing, a scanning module disposed interior to the housing, in a movable manner, and a control processing unit for controlling the scanning module and for processing a plurality of generated image data corresponding to a plurality of scanning positions. When the scanning module is moved to the plurality of scanning positions, the corresponding plurality of image data is generated. The control processing unit compares the plurality of generated image data, calculates differences between said plurality of generated image data, and moves the scanning module to a scanning position for scanning a document passing by the scanning window according to the calculated differences between said plurality of generated image data. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified diagram of a sheet-fed scanner of the prior art. 
         FIG. 2  is a diagram of an image datum when there is a dust grain at the under side of the transparent platform of the sheet-fed scanner shown in  FIG. 1 . 
         FIG. 3  is a diagram of a scanner according to a preferred embodiment of the present invention. 
         FIG. 4  is a diagram of a procedure of the scanning method according to a preferred embodiment of the present invention. 
         FIG. 5  is a diagram of a procedure according to another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 3 , which is a diagram of a scanner  300  according to a preferred embodiment of the present invention. The scanner  300  includes a housing  310 , a sheet-in tray  315 , a sheet-out tray  316 , a roller  325 , a first motor  330 , a transparent platform  335 , a light source  340 , a scanning module  345 , a memory  350 , a control circuit  355 , and a second motor  360 . 
     The first motor  330  is disposed interior to the housing  310  for rotating the roller  325  to move the to-be-scanned documents  320  to the transparent platform  335 . The second motor  360  is disposed interior to the housing  310  for moving the scanning module  345 . In an embodiment of the present invention, functions of the first motor  330  may directly be completed by the second motor  360 , and vice versa. The sheet-in tray  315  is connected to the housing  310  for storing a stack of the to-be-scanned documents  320 . The sheet-out tray  316  is also connected to the housing  310  for storing a stack of scanned documents  321 . The light source  340  is disposed interior to the housing  310  for providing required lights for scanning. The memory  350  is disposed interior to the housing  310  for storing generated image data of the stack of to-be-scanned documents  320 . 
     The scanning module  345  includes a photoelectric transforming element  346  and an analog-to-digital converter  347 . The photoelectric transforming element  346  includes a plurality of light sensing units  348 , which is disposed in a straight line substantially perpendicular to a direction of movement of the scanning module  345 . Each of the plurality of light sensing units  348  is for receiving lights, which are then transformed into corresponding analog image data by the photoelectric transforming element  346 . The analog-to-digital converter  347  is coupled to the photoelectric transforming element  346  for transforming the analog image data into corresponding digital image data, which are then stored in the memory  350 . 
     The control circuit  355  includes a microprocessor  357 , a first motor driving circuit  358 , and a second motor driving circuit  359 . The microprocessor  357  is for comparing digital image data stored in the memory  350  to generate a difference value, and for comparing the difference value with a predetermined critical value to determine whether the current scanning position of the scanning module  345  is appropriate for scanning the to-be-scanned documents  320 . The first motor driving circuit  358  is for driving the first motor  330  to rotate the roller  325  to move the to-be-scanned documents  320 . The second motor driving circuit  359  is for driving the second motor  360  to move the scanning module  345 . Moreover, the microprocessor  357  controls the second motor driving circuit  359  to drive the second motor  360  to move the scanning module  345  until the scanning module  345  reaches an appropriate scanning position. After the scanning module  345  reaches the appropriate scanning position, the microprocessor  357  controls the first motor driving circuit  358  to drive the first motor  330  to rotate the roller  325  to move the to-be-scanned documents  320  for being scanned. 
     Please refer to  FIG. 4 , which is a diagram of a procedure  499  of the scanning method according to a preferred embodiment of the present invention, where the procedure  499  may be regarded as a summary of the abovementioned descriptions of the scanning method of the present invention. The procedure  499  includes steps as follows: 
     Step  400 : Load the to-be-scanned documents  320  in the sheet-in tray  315  of the scanner  300 . 
     Step  405 : Initiate the scan procedure for the to-be-scanned documents  320 . 
     Step  410 : Control the second motor driving circuit  359  with the microprocessor  357  of the control circuit  355  to drive the second motor  360  to move the scanning module  345  to a first location. 
     Step  415 : Generate a first analog image datum by scanning a sheet of the to-be-scanned documents  320  with the scanning module  345  at the first location and transform the first analog image datum generated by the photoelectric transforming element  346  into a first digital image datum with the analog-to-digital converter  347 . 
     Step  420 : Store the first digital image datum in the memory  350 . 
     Step  425 : Control the second motor driving circuit  359  with the microprocessor  357  of the control circuit  355  to drive the second motor  360  to move the scanning module  345  to a second location. 
     Step  430 : Generate a second analog image datum by scanning the sheet of the to-be-scanned documents  320  with the scanning module  345  at the second location and transform the second analog image datum generated by the photoelectric transmitting element  346  into a second digital image datum with the analog-to-digital converter  347 . 
     Step  435 : Store the second digital image datum in the memory  350 . 
     Step  440 : Compare the first digital image datum with the second digital image datum by the microprocessor  357  of the control circuit  355  for generating a difference value. 
     Step  445 : Determine whether the generated difference value is smaller than a predetermined critical value with the microprocessor  357  of the control circuit  355 . When the difference value is smaller than the predetermined critical value, go to step  485 . Otherwise, go to Step  450 . 
     Step  450 : Control the second motor driving circuit  359  with the microprocessor  357  of the control circuit  355  to drive the second motor  360  to move the scanning module  345  to a next location from the second location. 
     Step  455 : Generate an analog image datum by scanning the sheet of the to-be-scanned documents  320  with the scanning module  345  at the next location and transforming the analog image datum generated by the photoelectric transmitting element  346  into a digital image datum with the analog-to-digital converter  347 . 
     Step  460 : Store the digital image datum in the memory  350 . 
     Step  465 : Compare the digital image data generated with respect to the second location and the next location with the microprocessor  357  of the control circuit  355  for generating a difference value. 
     Step  470 : Determine whether the difference value generated in Step  465  is smaller than a predetermined critical value with the microprocessor  357  of the control circuit  355 . When the difference value is smaller than the predetermined critical value, go to Step  485 . Otherwise, go to Step  475 . 
     Step  475 : When the number of times of moving the scanning module  345  is larger than a critical value, go to Step  480 . Otherwise, go to Step  450 . 
     Step  480 : Control the second motor driving circuit  359  to drive the second motor  360  to move the scanning module  345  to a predetermined location or to one of a plurality of previous locations, where the scanning module  345  has reached during scanning the sheet of the to-be-scanned documents  320 . 
     Step  485 : Control the first motor driving circuit  358  with the microprocessor  357  of the control circuit  355  to drive the first motor  330  to rotate the roller  325  to move the sheet of the to-be-scanned documents  320  along a Y-axis utilized by the scanning module  345  and across the transparent platform  335  so that the sheet of the to-be-scanned documents  320  may be scanned by the scanning module  345 . 
     Step  490 : Repeat Step  485  until all sheets of the to-be-scanned documents  320  are scanned. 
     According to another preferred embodiment of the present invention, the procedure  499  may further be adapted in a manner described later. Since the scanning module  345  scans lines one by one along a Y-axis, where each of the scanned lines stretches parallel to a X-axis orthogonal to the Y-axis and has a plurality of pixels. In Step  440 , the microprocessor  356  of the control circuit  355  compares the first digital image datum with the second digital image datum for outputting a difference value, which may be generated by calculating respective difference values or an accumulated difference value between the plurality of first pixels in the first digital image datum and the plurality of second pixels in the second digital image datum. That is, the microprocessor  357  of the control circuit  355  calculates a difference value between a first pixel and a second pixel, both of which lie on a Y-axis, or calculates an accumulated difference value between a plurality of first pixels and a plurality of second pixels corresponding to the plurality of first pixels, for generating the difference value. In Step  445 , the microprocessor  357  determines whether the calculated difference value between the first digital image datum and the second digital image datum is not larger than a predetermined critical value. 
     Similarly, in Step  465 , the microprocessor  357  compares the digital image datum at the second location and the digital image datum at the next location for generating a difference value, which may be generated by comparing pixels of the digital image datum at the second location and pixels of the digital image datum at the next location one by one, or by directly calculating an accumulated difference value between pixels of both the image data. In Step  470 , whether the generated difference value is not larger than a predetermined critical value is determined. 
     Please refer to  FIG. 5 , which is a diagram of a procedure  599  according to another preferred embodiment of the present invention. The procedure  599  includes steps as follows: 
     Step  500 : Load the to-be-scanned documents in the sheet-in tray  315  of the scanner  300 . 
     Step  505 : Initiate the scan procedure for the to-be-scanned documents  320 . 
     Step  510 : Control the second motor driving circuit  359  with the microprocessor  357  to drive the second motor  360  for moving the scanning module  345  to a first location. 
     Step  515 : Generate a first analog image datum by scanning at the first location of the scanning module  345  and transform the first analog image datum generated by the photoelectric transforming element  346  into a first digital image datum with the analog-to-digital converter  347 . 
     Step  520 : Store the first digital image datum in the memory  350 . 
     Step  525 : Control the second motor driving circuit  359  with the microprocessor  357  to drive the second motor  360  for moving the scanning module  345  to a second location. 
     Step  530 : Generate a second analog image datum by scanning at the second location of the scanning module  345  and transforming the second analog image datum generated by the photoelectric transforming element  346  into a second digital image datum with the analog-to-digital converter  347 . 
     Step  535 : Store the second digital image datum in the memory  350 . 
     Step  540 : Compare the first digital image datum with the second digital image datum with the microprocessor  357  for generating a difference value. 
     Step  545 : Determine whether the difference value is not larger than a predetermined critical value. When the difference value is not larger than the predetermined critical value, go to Step  585 . Otherwise, go to Step  546 . 
     Step  546 : Control the second motor driving circuit  359  to drive the second motor  360  for moving the scanning module  345  to a predetermined location or to the first location. 
     Step  585 : Control the first motor driving circuit  358  with the microprocessor  357  for driving the first motor  330  to rotate the roller  325  for moving the to-be-scanned documents  320  across the transparent platform  335  along a Y-axis so that the scanning module  345  can scan the to-be-scanned documents  320 . 
     Step  590 : Repeat Step  585  until the to-be-documents  320  are scanned completely. 
     The procedure  599  is described in detail as follows. The scanning module  345  scans along a Y-axis, where each image datum comprises a plurality of scan lines parallel to an X-axis orthogonal to the Y-axis and includes a plurality of pixels. In Step  540 , the microprocessor  357  compares a first digital image datum with a second digital image datum for generating a difference value. The difference value may be generated according to difference values between a plurality of pixels of the first digital image datum and a plurality of pixels of the second digital image datum, or be generated according to an accumulated difference value between pixels of both the first image datum and the second image datum. In Step  545 , the microprocessor  357  determines whether the generated difference value is not larger than a predetermined value. 
     In the abovementioned embodiments of the present invention, both the first motor  330  and the second motor  360  may be stepper motors or server motors, and may also be implemented with a same motor wringing with different gear wheels. Both the first motor driving circuit  358  and the second motor driving circuit  359  may be integrated into a same motor driving circuit on the control circuit  355 , and both of the first motor  330  and the second motor  360  may be initiated and switched with the aid of a switch on the integrated motor driving circuit. The light source  340  may be utilized in a reflective manner or in a transmissive manner for scanning documents, and moves synchronously with the scanning module  345 . 
     In summary, when there are dust grains adhering to the transparent platform  335  above or below, with the aid of the scanning method of the present invention, the scanning module  345  may still be moved to a location for scanning documents without being effected by the dust grains. Therefore, with the aid of the scanning method of the present invention, a scanner keeps an ideal scanning quality under non-ideal circumstances. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.