Abstract:
A color image reading apparatus includes a light source, first and second photoelectric conversion devices, first and second document size detection units and a control unit. The first photoelectric conversion device obtains first electric signal information at a first speed and the second photoelectric conversion device obtains second electric signal information at a second speed higher than the first speed. The first document size detection unit detects a document size based on the first electric signal information and the second document size detection unit detects a document size based on the second electric signal information. The control unit controls, at the time of forward scanning by the light source, so as to detect the document size by the second document detection unit.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a color image reading apparatus used for document reading of a digital copying machine and an input terminal of a personal computer and a document size detecting method in the color image reading apparatus. 
   2. Description of the Related Art 
   In a color image reading apparatus which is used for a digital copying machine or a personal computer and reads optical image information from a document using a color charge coupled device (hereinafter abbreviated to CCD), a document size detecting device for forward-scanning a document at the time of pre-scanning, deciding whether the document is a color document or a monochromatic document, at the time of backward scanning, detecting the document size on the decision level based on the obtained decision result, thereby preventing a misdetection is disclosed in Japanese Patent Publication 6-59351. However, this conventional document size detecting device detects first the document size at the time of backward scanning, so that the pre-scanning time for detecting the document size is prolonged and it is an obstacle to speeding up the image reading operation. 
   Furthermore, in a color image reading apparatus using a color CCD sensor, conventionally, regardless of a color document or a monochromatic document, an apparatus for detecting the document size by the color CCD sensor at the time of pre-scanning for detecting the document size is known. However, in this conventional apparatus, even for a monochromatic document the size of which can be originally detected in a short-time, the same detection time as that at the time of detection of the color document size is required to detect the document size. Therefore, in a monochromatic document, the pre-scanning time is wasted and speeding up of the reading operation is disturbed. 
   Therefore, in a color image reading apparatus using a color CCD sensor, it is desired to surely detect the document size regardless of a color document or a monochromatic document and shorten the pre-scanning time to speed up the image reading operation. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to shorten the document size detection time and speed up the image reading operation without impairing the accuracy of document size detection. 
   According to this embodiment of the present invention, the color image reading apparatus comprises a light source for irradiating a document relatively moving and scanning the document, a first photoelectric conversion device for receiving optical image information from the document and the background of the document by the light source and obtaining first electric signal information at a first speed, a second photoelectric conversion device for receiving the optical image information and obtaining second electric signal information at a second speed higher than the first speed, a first document size detection unit for detecting, on the basis of the first electric signal information from the first photoelectric conversion device, the boundary between the document and the background of the document and detecting the document size, a second document size detection unit for detecting, on the basis of the second electric signal information from the second photoelectric conversion device, the boundary between the document and the background of the document and detecting the document size, and a control unit for controlling, at the time of forward scanning of the document by the light source, so as to detect the document size using the second document size detection unit. 
   Further, according to the embodiment of the present invention, the document size detecting method in the color image reading apparatus having a first photoelectric conversion device for receiving optical image information from a document by a light source moving relatively to the document and obtaining electric signal information at a first speed and a second photoelectric conversion device for receiving the optical image information and obtaining the electric signal information at a second speed higher than the first speed, and detecting, on the basis of the first electric signal information from the first photoelectric conversion device, the boundary between the document and the background of the document, thereby detecting the document size or detecting, on the basis of the second electric signal information from the second photoelectric conversion device, the boundary between the document and the background of the document, thereby detecting the document size, at the time of forward scanning of the document by the light source, detects the document size on the basis of the second electric signal information from the second photoelectric conversion device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram showing a color scanner of the embodiment of the present invention, 
       FIG. 2  is a schematic plan view of a color scanner of the embodiment of the present invention viewed from the top, 
       FIG. 3  is a schematic block diagram showing a 4-line CCD sensor of the embodiment of the present invention, 
       FIG. 4  is a block diagram showing a document size detection control system of the embodiment of the present invention, 
       FIG. 5  is a flow chart showing the document size discrimination process of the embodiment of the present invention, and 
       FIG. 6  is a timing chart showing an output signal from a monochromatic CCD sensor of the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The embodiments of the present invention will be explained in detail hereunder with reference to the accompanying drawings.  FIG. 1  shows a color image reading apparatus of the embodiment of the present invention and it is a schematic block diagram showing a color scanner  10  used in combination with a digital color printer  50 . On the top of a body  1  of the color scanner  10 , as shown in  FIG. 2 , a document plate  11  made of a transparent glass plate and a platen sheet  12  covering overall the document plate  11  are installed. A coating face  12   a  of the platen sheet  12  as a background of a document D loaded on the document plate  11  is composed of a colored plastic sheet material. Furthermore, on the top of the body  1 , a control panel  2  having a ten-key pad  2   a,  a display panel  2   b,  and a start button  2   c  is installed. 
   Under the document plate  11 , an optical unit  13  for irradiating light to the document D on the document plate  11  and detecting reflected light from the document D which is optical image information is installed. The optical unit  13  has a first carriage  17  for loading a xenon lamp  14  which is a light source and a first mirror  16 , a second carriage  21  for loading a second and a third mirror  18  and  20 , a focusing lens  22 , and a 4-line CCD sensor  23  which is a photoelectric conversion device. The first carriage  17  and the second carriage  21  move back and forth by driving by a pulse motor  31  in the sub-scanning direction of the document plate  11 . A control unit  30  for controlling the body of the color scanner  10  controls the pulse motor  31 . 
   The 4-line CCD sensor  23 , as shown in  FIG. 3 , is composed of 4 lines such as 3 lines of R (red), G (green), and B (blue) of color CCD sensors  24 ,  26 , and  27  and 1 line of a monochromatic CCD sensor  28 . 
   The respective CCD sensors  24  to  28  are structured so that for example, the size of one pixel is 8×8 μm, and the number of pixels of one line is 8000, and the line interval is 32 μm. The image reading speed of the color CCD sensors  24  to  27  is the first speed of 105 mm/s. On the other hand, the monochromatic CCD sensor  28  outputs by dividing into two parts of odd pixels and even pixels, so that the image reading speed thereof is the second speed of 210 mm/s which is two times of that of the color CCD sensors  24  to  27 . 
   The 4-line CCD sensor  23  receives the reflected light from the document D, which is separated into R, G, and B, by the 3 lines of the color CCD sensors  24 ,  26 , and  27 , receives the reflected light, which is not separated, by the monochromatic CCD sensor  28 , and photo-electrically converts them respectively to output signals which are electric signal information. The output signals from the CCD sensors  24  to  28  are subject to the signal processes such as adjustment of the amplification factor for each sensitivity of the CCD sensors  24  to  28 , A-C conversion, and shading correction by a CCD control substrate  32  and transferred to the digital color printer  50  for image forming. 
     FIG. 4  is a block diagram showing a document size detection control system  29  for executing size detection of the document D on the document plate  11  by the control unit  30  for controlling the whole color scanner  10 . The control unit  30  is connected to the ten-key pad  2   a , the display panel  2   b , and the start button  2   c  on the control panel  2 , and a pulse motor  31  or the CCD control substrate  32  and controls the entire color scanner  10 . 
   The document size detection control system  29  has a first document size detection unit  36 . The first document size detection unit  36  has a first boundary detection circuit  33  for detecting the boundary between the coating face  12   a  of the platen sheet  12  and the document D from color output signals from the color CCD sensors  24  to  27  which are processed by the CCD control substrate  32  and a first latch circuit  34  for latching the address of the color CCD sensors  24  to  27  corresponding to the boundary obtained by the first boundary detection circuit  33  and inputting them to the control unit  30 . 
   Further, the document size detection control system  29  has a second document size detection unit  40 . The second document size detection unit  40  has a second boundary detection circuit  37  for detecting the boundary between the coating face  12   a  of the platen sheet  12  and the document D from a monochromatic output signal from the monochromatic CCD sensor  28  which is processed by the CCD control substrate  32  and a second latch circuit  38  for latching the address of the monochromatic CCD sensor  28  corresponding to the boundary obtained by the second boundary detection circuit  37  and inputting it to the control unit  30 . Furthermore, the document size detection control system  29  has a size discrimination circuit  42  for comparing whether the document size obtained from the address input from the first latch circuit  34  or the second latch circuit  38  is equivalent to the figurate paper size stored in a memory  41  of the control unit  30  beforehand or not and discriminating that the document D is of a predetermined size. The first boundary detection circuit  33  and the second boundary detection circuit  37  detect the document size by detecting changes in the reflection factor generated in the boundary position between the coating face  12   a  of the platen sheet  12  and the document D by the CCD sensors  24  to  28 . 
   The control unit  30 , at the time of pre-scanning before image reading scanning by the CCD sensors  24  to  28 , when forward scanning the document D by the optical unit  13 , sets the pulse motor  31  and the CCD control substrate  32  so as to detect the document size using the second document size detection unit  40  for detecting the document size on the basis of an output signal from the monochromatic CCD sensor  28 . Namely, to detect the document size on the basis of the output signal from the monochromatic CCD sensor  28 , the control unit  30  controls the pulse motor  31  so as to scan at a speed of 210 mm/s by the optical unit  13 . 
   However, at the time of document size detection using the monochromatic CCD sensor  28 , when the document D is a color document, depending on color tone and color strength, the boundary between the coating face  12   a  of the platen sheet  12  and the document D cannot be detected and impossibility of document size detection may be caused. When the document size cannot be detected at the time of forward scanning of pre-scanning like this, the control unit  30  sets the pulse motor  31  and the CCD control substrate  32  so as to detect the document size using the first document size detection unit  36  for scanning the document D again at the time of backward operation of the optical unit  13  of pre-scanning and detecting the document size on the basis of output signals from the color CCD sensors  24  to  27 . Namely, to detect the document size on the basis of the output signals from the color CCD sensors  24  to  27 , the control unit  30  controls the pulse motor  31  so as to scan at a speed of 105 mm/s by the optical unit  13 . 
   Further, when the document size can be detected at the time of forward scanning of pre-scanning, the control unit  30  controls the pulse motor  31  so as to return the optical unit  13  to the wait position at the same speed of 210 mm/s as that of forward scanning without executing backward scanning to obtain output signals from the color CCD sensors  24  to  27 . 
   The color scanner  10  structured in this way, at the start time of image reading, pre-scans the document plate  11 , discriminates the document size, and then starts the document D reading operation. Next, the document size discrimination process by pre-scanning will be described by referring to the flow chart shown in  FIG. 5 . When the image reading operation is started, at Step  100 , the process compares whether the operation mode is the document size discrimination mode or not. When the document size is not set on the control panel  2  and it must be discriminated, the process goes to Step  101 . On the other hand, when an operator sets the document size from the control panel  2  and the document size discrimination scanning is not necessary, the process goes to Step  120 . 
   When the start button  2   c  is turned on at Step  101 , Pre-scan for detecting the document size is set and at Step  102 , the first and second carriages  17  and  21  are initialized to the start positions indicated by dotted lines shown in  FIG. 1 . At Step  103 , to select the second document size detection unit  40  using the monochromatic CCD sensor  28  and detect the document size, the pulse motor  31  or the CCD control substrate  32  is set. At Step  104 , the xenon lamp  14  is turned on, and the first and second carriages  17  and  21  perform the forward operation from the start positions in the direction of the arrow s at a speed of 210 mm/s and forward scan the document D on the document plate  11  and the platen sheet  12 . At Step  106 , the monochromatic CCD sensor  28  sequentially reads the reflected light from the document D and the platen sheet  12  and at Step  107 , it discriminates the document size. 
   Namely, at Step  106 , by forward scanning of the document D and the platen sheet  12 , from the monochromatic CCD sensor  28 , the output signal shown in the timing chart in  FIG. 6  is output. The second boundary detection circuit  37  is in the boundary position between the coating face  12   a  of the platen sheet  12  and the document D and outputs (A) and (B) shown in  FIG. 6  the output voltage of which varies from v 1  to v 2  or from v 2  to v 1 . The second latch circuit  38  recognizes and latches the output timing from the second boundary detection circuit  37  as addresses of the monochromatic CCD sensor  28  equivalent to the front end (A 1 ) and rear end (B 1 ) of the document D in the main scanning direction and inputs it to the control unit  30 . 
   At the same time, the second latch circuit  38  recognizes and latches the timing that the boundary positions (A) and (B) between the area of the coating face  12   a  of the platen sheet  12  and the area of the document D are not output during forward moving of the first and second carriages  17  and  21  as an address indicating the end of the document D in the sub-scanning direction and inputs it to the control unit  30 . For the timing in the sub-scanning direction, the pulse of the pulse motor  31  is used. 
   At Step  107 , the control unit  30  recognizes the area of the document D by address input from the second latch circuit  38 , compares it with the figurate paper size stored in the memory  41  by the size discrimination circuit  42 , thereby discriminates the size of the document D. In the size discrimination circuit  42 , when the area of the document D coincides with the figurate paper size and the document size can be discriminated, the process goes to Step  108 . When the area of the document D cannot be recognized or the recognized area of the document D does not coincide with the figurate paper size in the size discrimination circuit  42  and the document size cannot be discriminated, the process goes to Step  113 . 
   At Step  108 , the xenon lamp  14  is turned off, and the first and second carriages  17  and  21  perform the backward operation at the same speed of 210 mm/s as that of the forward operation in the direction of the arrow t and return to the wait position, and at Step  110 , the document size is decided, and the pre-scanning is finished, and at Step  111 , the image reading operation is started. At Step  113 , the document size detection using the monochromatic CCD sensor  28  at the time of forward scanning is switched to the document size detection using the color CCD sensors  24  to  27  and backward scanning is executed. 
   At Step  113 , the first document size detection unit  36  using the color CCD sensors  24  to  27  is selected and the pulse motor  31  or the CCD control substrate  32  is set. At Step  114 , the xenon lamp  14  is turned on, and the first and second carriages  17  and  21  perform the backward operation at a speed of 105 mm/s, which is ½ of that of the forward operation, in the direction of the arrow t, and the document D on the document plate  11  and the platen sheet  12  are  10  backward scanned. At Step  116 , in the same way as with Step  106 , the color CCD sensors  24  to  27  sequentially read the reflected light from the document D and the platen sheet  12  and at Step  117 , in the same way as with Step  107 , discriminate the document size. 
   At Step  116 , in place of the second document size detection  115  unit  40  at Step  106 , the first document size detection unit  36  latches the boundary address between the coating face  12   a  of the platen sheet  12  and the document D and inputs it to the control unit  30 . At Step  117 , the control unit  30  recognizes the area of the document D from the input address and discriminates in the size discrimination circuit  42  whether it is equivalent to the figurate paper size stored in the memory  41  or not, and when the area of the document D recognized by output signals from the color CCD sensors  24  to  27  coincides with the figurate paper size and the document size can be discriminated, the process goes to Step  110 . 
   At Step  110 , the document size is decided and the pre-scanning is finished. At Step  117 , when the area of the document D cannot be recognized even by the color CCD sensors  24  to  27  or the recognized area of the document D does not coincide with the figurate paper size and the document size cannot be discriminated, the process goes to Step  118 . At Step  118 , a document size detection error is displayed on the display panel b. Further, when the document size discrimination mode is not set at the start time of the image reading operation, by turning the start button  2   c  on at Step  120 , the image reading mode is set and at Step  121 , the first and second carriages  17  and  21  are initialized to the start positions indicated by dotted lines shown in  FIG. 1  by the pulse motor  31 . Next, the image reading operation is started at Step  111  without pre-scanning. 
   According to this embodiment, the color scanner  10 , regardless of the kind of document D, at the time of forward scanning of pre-scanning, discriminates the document size on the basis of an output signal from the monochromatic CCD sensor  28 . When a discrimination error of the document size is caused in the monochromatic CCD sensor  28 , during the backward operation of pre-scanning, the color scanner  10  scans the document D again using the color CCD sensors  24  to  27  and detects the document size on the basis of output signals from the color CCD sensors  24  to  27 . Further, when the document size can be discriminated by forward scanning of pre-scanning, at the time of the backward operation of pre-scanning, the color scanner  10  does not scan the document D and returns the optical unit  13  to its wait position. 
   Therefore, when the discrimination of the document size is finished only by forward scanning using the high-speed monochromatic CCD sensor  28 , the optical unit  13  can be returned to its wait position at high speed, and the pre-scanning time is shortened, thus the reading operation can be speeded up. Moreover, when the document size cannot be detected by the monochromatic CCD sensor  28 , during the backward operation, the document size detection is executed again using the color CCD sensors  24  to  27  capable of surely detecting even a color document, thus the document size can be surely discriminated and the apparatus can respond to diversification of documents. 
   Further, the present invention is not limited to the aforementioned embodiments and it can be changed within a range which is not deviated from the objects of the present invention. For example, the light source of the color image reading apparatus, if the photoelectric conversion device can detect light from a document, may be a halogen lamp and the optical image information may be transmitted light from a document instead of reflected light. Further, the size of pixels of the photoelectric conversion device and the number of pixels are not limited. Furthermore, with respect to the platen sheet which is a background of a document, if a difference in the reflection factor from the document or the transmission factor can be made clear, the material thereof is optional and may be matte-finished. 
   As mentioned above in detail, according to the present invention, at the time of document size detection of the color image reading apparatus, forward scanning is executed using the high-speed photoelectric conversion device for reading a monochromatic image and the pre-scanning time is shortened, thus the image reading operation can be speeded up. Further, when a document size detection error is caused during the forward operation by the high-speed photoelectric conversion device, the document size detection is executed using the photoelectric conversion device for surely reading a color image, thus the document size can be surely detected regardless of the document kind and the apparatus can respond to diversification of document kinds.