Abstract:
An image-reading device includes a plurality of image sensor chips, a switch, an output selector and a controller. The plurality of image sensor chips is juxtaposed along a line extending in a widthwise direction of an original document carrying images thereon. Each image sensor chip includes a plurality of image sensors, reads the images on the original document, and generates image signals. The switch is configured to combine at least two image sensor chips into one virtual image sensor chip. The output selector allows the image signals from the virtual image sensor chip and remaining image sensor chip to be outputted. The controller controls the switch depending on the width of the original document, and controls, depending on the width of the original document, the output selector to allow the image signals to be outputted.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an image-reading device, and particularly to an image-reading device employing a contact image sensor (CIS) having a plurality of image sensor integrated circuits (IC) chips arranged linearly.  
         [0003]     2. Description of Related Art  
         [0004]     A conventional image-reading device such as that disclosed in Japanese unexamined patent application publication No. SHO-63-20952 includes a contact image sensor having a plurality of image sensor IC chips arranged linearly. In the example shown in  FIG. 1 , trigger signals TG 1 , TG 2 , and TG 3  are inputted simultaneously into image sensor IC chips CH 1 , CH 2 , and CH 3  so that image signals AO 1 , AO 2 , and AO 3  are read in parallel from the image sensor IC chips CH 1 , CH 2 , and CH 3 .  
         [0005]     One conventional image-reading device disclosed in Japanese unexamined patent application publication No. 2003-298813 includes a contact image sensor having a plurality of image sensor IC chips arranged linearly and divided into blocks of a natural multiple of three. Each block outputs an image signal to a triple-channel analog front end (AFE), thereby improving the speed for reading image signals. The triple-channel AFE is widely used in image-reading devices because, along with single-channel AFEs, triple-channel AFEs are more popular than AFEs having another number of channels and are mass-produced and, therefore, less expensive.  
         [0006]     However, this conventional technology can only read an image at one speed, even when the original document is of a narrower width that does not require all image sensor IC chips. Accordingly, the time required to read an image with this conventional image-reading device is governed by the number of pixels in each image sensor IC chip if all chips have the same number, or by the number of pixels in the image sensor IC chip having the largest number when the number of pixels is not uniform.  
       SUMMARY OF THE INVENTION  
       [0007]     In view of the above-described drawbacks, it is an objective of the present invention to provide an image-reading device capable of reading a narrow original faster.  
         [0008]     In order to attain the above and other objects, the present invention provides an image-reading device including a plurality of image sensor chips, a switch, an output selector and a controller. The plurality of image sensor chips is juxtaposed along a line extending in a widthwise direction of an original document carrying images thereon. Each image sensor chip includes a plurality of image sensors, reads the images on the original document, and generates image signals. The switch is configured to combine at least two image sensor chips into one virtual image sensor chip. The output selector allows the image signals from the virtual image sensor chip and remaining image sensor chip to be outputted. The controller controls the switch depending on the width of the original document, and controls, depending on the width of the original document, the output selector to allow the image signals to be outputted.  
         [0009]     Another aspect of the present invention provides an image-reading device including a plurality of image sensor units, a switch, an output selector and a controller. The plurality of image sensor units is juxtaposed along a line extending in a widthwise direction of an original document carrying images thereon. Each image sensor unit includes a plurality of image sensors, reads the images on the original document, and generates image signals. The switch is configured to divide the image sensor unit into a plurality of sensor segments so that each sensor segment includes at least one of the image sensors. The output selector allows the image signals from the sensor segment and remaining image sensor unit to be outputted. The controller controls the switch depending on the width of the original document, and controls, depending on the width of the original document, the output selector to allow the image signals to be outputted. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings in which:  
         [0011]      FIG. 1  is a block diagram showing a structure of a conventional image-reading device;  
         [0012]      FIG. 2  is a perspective view of a multifunction device incorporating an image-reading device according to a preferred embodiment of the present invention;  
         [0013]      FIG. 3  is a cross-sectional view of the image-reading device according to the preferred embodiment;  
         [0014]      FIG. 4  is a perspective view of a contact image sensor shown in  FIG. 3 ;  
         [0015]      FIG. 5  is a block diagram showing an electrical configuration of the image-reading device according to the preferred embodiment;  
         [0016]      FIG. 6  is a circuit diagram illustrating an example structure of image sensor IC chips shown in  FIG. 5 ;  
         [0017]      FIG. 7  is a block diagram showing a configuration of the image-reading device according to the preferred embodiment;  
         [0018]      FIG. 8  is a block diagram showing a switching state when reading an A3-size original with the image-reading device shown in  FIG. 7 ;  
         [0019]      FIG. 9  is a block diagram showing a switching state when reading a left-justified A4-size original with the image-reading device shown in  FIG. 7 ; and  
         [0020]      FIG. 10  is a block diagram showing a switching state when reading a centered A4-size original with the image-reading device shown in  FIG. 7 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     An image-reading device according to preferred embodiments of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description.  
         [0022]      FIG. 2  is a perspective view of a multifunction device  1  incorporating an image-reading device  10  according to the preferred embodiment. The multifunction device  1  has a clamshell structure configured of a lower casing  1   a , and an upper casing  1   b  mounted on the lower casing  1   a  and being capable of opening and closing thereon. The image-reading device  10  is provided in the upper casing  1   b . A control panel  2  is also provided on a front surface side of the upper casing  1   b . The multifunction device  1  also includes a laser printer or other image-forming device in addition to the image-reading device  10 . However, since this image-forming device is not directly related to the present invention, the device will not be described herein.  
         [0023]      FIG. 3  is a cross-sectional view of the image-reading device  10 . As shown in  FIG. 3 , the image-reading device  10  includes a flatbed mechanism and an automatic document feeder (ADF). The image-reading device  10  itself also has a clamshell structure configured of a flatbed unit  10   a  and a cover  10   b  attached to the flatbed unit  10   a  and capable of opening and closing thereon.  
         [0024]     The flatbed unit  10   a  includes a contact image sensor  12  and a platen glass  14 . The cover  10   b  includes an original tray  16 , an original conveying device  18 , and an original receiving tray  20 .  
         [0025]     The contact image sensor  12  includes light-receiving elements  22 , such as photodetectors, a SELFOC lens  24 , and a light source  26 . The light source  26  irradiates light onto the original document at a reading position, and the light-receiving elements  22  receive the light reflected off the original through the SELFOC lens  24 . The contact image sensor  12  is configured to read an image based on the results of light received by the light-receiving elements  22 . A driving mechanism (not shown) is also provided for driving the contact image sensor  12  to reciprocate in the left-to-right direction in  FIG. 3  so that the light-receiving elements  22  are moved directly below the reading position in the actual reading process.  
         [0026]     As shown in  FIGS. 4 and 5 , the contact image sensor  12  is mounted on the surface of a substrate  30  and includes five image sensor IC chips ch 1 -ch 5  aligned in a single row and having light-receiving elements that are also arranged linearly. Each of the image sensor IC chips ch 1 -ch 5  is rectangular in shape and includes a plurality of light-receiving elements spaced at intervals in a single row. In the preferred embodiment, A3-size and A4-size sheets are disposed so that a direction in which a short dimension of the A3-size or A4-size sheets extends is identical to a direction in which the image sensor IC chips ch 1 -ch 5  are arranged. The contact image sensor  12  is configured to support reading of an original having a width equivalent to an A3-size sheet. Each of the image sensor IC chips ch 1 -ch 5  has a resolution of 1200 dpi (47.2 dot/mm). As shown in  FIG. 7 , the image sensor IC chip ch 1  has light-receiving elements for 2,126 pixels; the image sensor IC chip ch 2  for 3,976 pixels, the image sensor IC chip ch 3  for 3,976 pixels; the image sensor IC chip ch 4  for 2,126 pixels; and the image sensor IC chip ch 5  for 2,126 pixels. Hence, the contact image sensor  12  has a total of 14,330 light-receiving elements spaced at intervals in a single line.  
         [0027]     As shown in  FIG. 6 , each of the image sensor IC chips ch 1 -ch 5  has phototransistors PT 1 -PTn constituting the respective prescribed number of light-receiving elements. Upon receiving light, the phototransistors PT 1 -PTn store an electric charge corresponding to the amount of received light. The basic circuit structure of the image sensor IC chips ch 1 -ch 5  themselves is identical to the conventional image sensor IC chips. When a trigger signal TG outputted from a control circuit  41  described later is inputted into the image sensor IC chip, a shift register  29  provided in the chip sequentially turns on a plurality of field effect transistors FET 1 -FETn in a fixed direction according to an inputted clock signal CLK. As a result, the electric charges stored in the phototransistors PT 1 -PTn are discharged in a fixed sequence. The electric charges are amplified by an amplifier OP and outputted serially as image signal AO 1  to A 05  from the image sensor IC chips ch 1 -ch 5  respectively. The image signals AO 1  to A 05  are analog signals. The image sensor IC chips ch 1 -ch 5  also include a voltage terminal VDD for supplying a drive voltage as required power for operating the components in the image sensor IC chips ch 1 -ch 5 , and a terminal GND connected to ground.  
         [0028]     As shown in  FIG. 5 , the connector  31  is provided on an edge of the substrate  30 ; and switches SW 1 , SW 2 , and SW 3  and an image signal selecting circuit  32  are provided on the same surface of the substrate  30  as the contact image sensor  12 . These components are connected by a wiring pattern. One end of the wiring pattern is connected to the connector  31  so that a device external to the substrate  30  connected to the connector  31  via a cable (not shown) can supply power to and exchange signals with the image sensor IC chips ch 1 -ch 5 .  
         [0029]     The image-reading device  10  includes the triple-channel AFE  40 , the clock control circuit  41  and a memory device  43 . The triple-channel AFE  40  and the clock control circuit  41  are connected to the connector  31  of the substrate  30 . The triple-channel AFE  40  is configured of an analog/digital (A/D) converter  42  and a timing control circuit  44 .  
         [0030]     The switch SW 1  has a first input terminal connected to the image sensor IC chip ch 1 , a second input terminal connected to the control circuit  41  for receiving the trigger signal TG therefrom, and a switch terminal connected to the image sensor IC chip ch 2 . The switch SW 1  is switched according to a control signal CO 1  inputted from the control circuit  41  to select whether to input a trigger signal TG 1  (outputted from the image sensor IC chip ch 1  after the image sensor IC chip ch 1  reads the image) or a trigger signal TG 2  into the image sensor IC chip ch 2 .  
         [0031]     The switch SW 2  has a switch terminal connected to the image sensor IC chip ch 1  for receiving the image signal A 01  shifted out from the image sensor IC chip ch 1 , a first output terminal connected to the image sensor IC chip ch 2 , and a second output terminal connected to the image signal selecting circuit  32 . The switch SW 2  is switched according to a control signal control signal CO 2  inputted from the control circuit  41  to select whether to serially input the image signal AO 1  outputted from the image sensor IC chip ch 1  into the image sensor IC chip ch 2  or whether to output the image signal A 01  as is.  
         [0032]     The switch SW 3  has a switch terminal connected to the image sensor IC chip ch 4  for receiving the image signal A 04  shifted out from the image sensor IC chip ch 4 , a first output terminal connected to the image sensor IC chip ch 5 , and a second output terminal connected to the image signal selecting circuit  32 . The switch SW 3  is switched according to the control signal CO 2  inputted from the control circuit  41  to select whether to serially input an image signal AO 4  outputted from the image sensor IC chip ch 4  into the image sensor IC chip ch 5  or whether to output the image signal image signal A 4  as is. Hence, the switches SW 2  and SW 3  are switched in association with each other by the control signal CO 2 .  
         [0033]     While not shown in detail in the drawings, the image signal selecting circuit  32  has five input terminals and three output terminals. The first input terminal of the image signal selecting circuit  32  is connected to the second output terminal of the switch SW 2 ; the second input terminal to an output terminal of the image sensor IC chip ch 2 ; the third input terminal to an output terminal of the image sensor IC chip ch 3 ; the fourth input terminal to the second output terminal of the switch SW 3 ; and the fifth input terminal to an output terminal of the image sensor IC chip ch 5 . The first, second, and third output terminals of the image signal selecting circuit  32  are all connected to the A/D converter  42  via the connector  31 . The image signal selecting circuit  32  selects three image signals among the image signals that are inputted therein according to a control signal CO 3  inputted from the control circuit  41 , and outputs the three signals to the A/D converter  42  via the connector  31 .  
         [0034]     The control circuit  41  is configured to transmit the trigger signal TG and the clock signal CLK to the connector  31 . The trigger signal TG is inputted into the image sensor IC chip ch 1  as the trigger signal TG 1 , into the image sensor IC chip ch 3  as a trigger signal TG 3 , and into the image sensor IC chip ch 4  as a trigger signal TG 4 . The trigger signal TG can also be inputted into the image sensor IC chip ch 2  via the switch SW 1  as the trigger signal TG 2  after the image sensor IC chip ch 1  reads the image. The clock signal CLK is inputted into each of the image sensor IC chips ch 1 -ch 5 . The control circuit  41  also outputs the control signal CO 1  for switching the switch SW 1 , the control signal CO 2  for switching the switches SW 2  and SW 3 , and the control signal CO 3  for switching the image signal selecting circuit  32 . The signal lines for the control signals CO 1 , CO 2 , and CO 3  are indicated by dotted lines in  FIG. 5  merely to help distinguish them from the other lines.  
         [0035]     The A/D converter  42  is a triple-channel device capable of converting three analog signals to digital signals in parallel. The multiplexer  44  functions to multiplex three image signals converted to digital signals by the A/D converter  42  and output the multiplexed signals to the memory device  43 .  
         [0036]     The memory device  43  is configured of a random access memory (RAM), for example, and functions to store data of signals converted to digital data by the A/D converter  42  and multiplexed by the multiplexer  44  in association with addresses. The clock control circuit  41  also functions to control data that is read from the memory device  43  so that one line worth of image signals converted to digital data is outputted from the memory device  43  in a prescribed sequence. The sequence of the image signals is identical to the sequence in which the image signals were obtained when the fifteen image sensor IC chips ch 1 -ch 5  are driven one at a time in order, for example.  
         [0037]     As shown in  FIG. 7 , the contact image sensor  12  includes the image sensor IC chip ch 1  for 2,126 pixels, the image sensor IC chip ch 2  for 3,976 pixels, the image sensor IC chip ch 3  for 3,976 pixels, the image sensor IC chip ch 4  for 2,126 pixels, and the image sensor IC chip ch 5  for 2,126 pixels arranged linearly from left to right in the order given. Between the image sensor IC chips ch 1  and ch 2  are provided the switch SW 1  for determining whether to input the trigger signal TG 1  outputted from the image sensor IC chip ch 1  into the image sensor IC chip ch 2  or to input the trigger signal TG 2  into the image sensor IC chip ch 2 ; and the switch SW 2  for determining whether to shift in the image signal image signal A 01  shifted out from the image sensor IC chip ch 1  into the image sensor IC chip ch 2  or to output the image signal A 01  directly. Further, between the image sensor IC chips ch 4  and ch 5  is provided the switch SW 3  for determining whether to shift in the image signal AO 4  shifted out from the image sensor IC chip ch 4  into the image sensor IC chip ch 5  or to output the image signal AO 4  directly.  
         [0038]     Next, the operations of the image-reading device  10  according to the preferred embodiment will be described. Note that the image-reading device  10  is provided with a size input unit (not shown) into which a user inputs the size of the original and the position of the original, that is, whether the original is left-justified or centered.  
         [0039]     (1) Reading an A3-Size Original (See  FIG. 8 )  
         [0040]     All of the image IC chips ch 1  to ch 5  reads the image when reading an A3-size original. As shown in  FIG. 8 , when reading an A3-size original, the control circuit  41  switches the switch SW 1  with the control signal CO 1  so that the trigger signal TG 1  outputted from the image sensor IC chip ch 1  is inputted into the image sensor IC chip ch 2 . With the control signal CO 2 , the control circuit  41  also switches the switch SW 2  so that the image signal A 01  serially outputted from the image sensor IC chip ch 1  is serially inputted into the image sensor IC chip ch 2 , and switches the switch S 3  so that the image signal AO 4  outputted from the image sensor IC chip ch 4  is serially inputted into the image sensor IC chip ch 5 . The control circuit  41  controls the image signal selecting circuit  32  with the control signal CO 3  to select and output the image signals AO 2 , AO 3 , and AO 5 .  
         [0041]     As a result, the image signal A 02  is serially outputted from the image sensor IC chips ch 1  and ch 2 , the image signal A 03  is serially outputted from the image sensor IC chip ch 3 , and the image signal A 05  is serially outputted from the image sensor IC chips ch 4  and ch 5 .  
         [0042]     The link between the image sensor IC chips ch 1  and ch 2  has the maximum number of pixels for reading an A3-size original. Hence, the time required for reading the A3-size original is the shift-out time that the image sensor IC chips ch 1  and ch 2  take to read the image. In other word, the time required for reading an A3-size original is determined by the total number of pixels for the image sensor IC chips ch 1  and ch 2  (6,102 pixels)×the pixel period.  
         [0043]     (2) Reading a Left-justified A4-Size Original (See  FIG. 9 )  
         [0044]     The image IC chips ch 1 , ch 2  and ch 3  read the image when reading a left-justified A4-size original. As shown in  FIG. 9 , when reading the left-justified A4-size original, the control circuit  41  switches the switch SW 1  with the control signal CO 1  so as to input the trigger signal TG 2  into the image sensor IC chip ch 2 . The control circuit  41  also switches the switch SW 2  with the control signal CO 2  so as to output the image signal A 01  serially outputted from the image sensor IC chip ch 1  to the image signal selecting circuit  32  and switches the switch SW 3  so as to output the image signal AO 4  serially outputted from the image sensor IC chip ch 4  to the image signal selecting circuit  32 . The control circuit  41  also controls the image signal selecting circuit  32  with the control signal CO 3  to select and output the image signals A 01 , AO 2 , and AO 3 .  
         [0045]     As a result, the image signal A 01  serially outputted from the image sensor IC chip ch 1 , the image signal A 02  serially outputted from the image sensor IC chip ch 2 , and the image signal A 03  serially outputted from the image sensor IC chip ch 3  are outputted to the triple-channel AFE  40 .  
         [0046]     The image sensor IC chip ch 2  or ch 3  has the maximum number of pixels for reading the left-justified A4-size original. Hence, the time required for reading the left-justified A4-size original is the shift-out time that the image sensor IC chip ch 2  or ch 3  takes to read the image. In other word, the time required for reading the left-justified A4-size original is determined by the number of pixels in the image sensor IC chip ch 2  or ch 3  (3,976)×the pixel period. The time required for reading the left-justified A4-size original is about two-thirds the time required for reading the A3-size original.  
         [0047]     (3) Reading a Centered A4-Size Original (See  FIG. 20 )  
         [0048]     The image IC chips ch 2 , ch 3  and ch 4  read the image when reading a centered A4-size original. As shown in  FIG. 10 , when reading a centered A4-size original, the control circuit  41  switches the switch SW 1  with the control signal CO 1  so as to input the trigger signal TG 2  into the image sensor IC chip ch 2 . The control circuit  41  also switches the switch SW 2  with the control signal CO 2  so as to output the image signal A 01  serially outputted from the image sensor IC chip ch 1  to the image signal selecting circuit  32  and to switch the switch SW 3  so as to output the image signal AO 4  serially outputted from the image sensor IC chip ch 4  to the image signal selecting circuit  32 . The control circuit  41  also controls the image signal selecting circuit  32  with the control signal CO 3  to select and output the image signals A 02 , AO 3 , and AO 4 .  
         [0049]     As a result, the image signal A 02  serially outputted from the image sensor IC chip ch 2 , the image signal A 03  serially outputted from the image sensor IC chip ch 3 , and the image signal A 04  serially outputted from the image sensor IC chip ch 4  are outputted to the triple-channel AFE  40 .  
         [0050]     The image sensor IC chip ch 2  or ch 3  has the maximum number of pixels for reading the centered A4-size original. Hence, the time required for reading the centered A4-size original is the shift-out time that the image sensor IC chip ch 2  or ch 3  takes to read the image. In other word, the time required for reading the centered A4-size original is determined by the number of pixels in the image sensor IC chip ch 2  or ch 3  (3,976)×the pixel period. The time required for reading the centered A 4  size original is about two-thirds the time required for reading the A3-size original.  
         [0051]     Hence, the time required for reading image signals of an A4-size original is approximately two-thirds the time required for reading an A3-size original, thereby increasing the reading speed for an A4-size original. Further, when reading an A4-size original, the image-reading device  1  can read the original faster than when reading an A3-size original, whether the original is left-justified or centered.  
         [0052]     With this construction, the image-reading device  1  can output image signals from the image sensor IC chips in parallel when the original has a narrower width by switching the connection state among the image sensor IC chips according to the width of the original being read. Since the reading time is governed by the image sensor IC chip reading the largest number of pixels, the present invention can reduce the image-reading time in comparison to the time required to read an original of the maximum width.  
         [0053]     Since these image sensor IC chips ch 1  to ch 5  are arranged in the order m-pixel type, n-pixel type, n-pixel type, m-pixel type, and m-pixel type (m=2126, n=3976 in the preferred embodiment), the number of pixels in one line of a narrow original having a narrower width than an original-supporting surface for supporting an original having the maximum width can be set to (m+2n) pixels whether the narrow original is left-justified or centered on the original-supporting surface, making the image-reading process more versatile.  
         [0054]     The image-reading device  1  can read image signals on three channels, whether the image signals are for an original of the maximum width or for an original of a narrow width. Hence, while the conventional image-reading device cannot read an original in a shorter time than the maximum number of pixels in image sensor IC chips for a maximum size original×the pixel period, the image-reading device  1  can read an original of a narrower width than the maximum width at the maximum number of pixels in image sensor IC chips for the narrow original×the pixel period. Using m and n as the number of pixels in the image sensor IC chips, the maximum number of pixels×the pixel period in this case can be calculated as {⅓·(3m+2n)}=(m+⅔·n).  
         [0055]     The image-reading device  1  can read an original with three channels, whether the original is an A3-size original or an A4-size original. Hence, while the conventional image-reading device cannot read an original in a shorter time than (m+⅔·n) pixels×the pixel period, the image-reading device  1  can read an A4-size original at n pixels×the pixel period. Further, when reading an A4-size original, the image-reading device  1  achieves the same effects whether the original is left-justified or centered.  
         [0056]     Since the image-reading device  1  performs image reading over the entire width of the original using all pixels in the image sensor IC chips, the image-reading device  1  can read an original having the maximum width in a time period equivalent to the maximum number of pixels in image sensor IC chips for reading an original of the maximum width×the pixel period.  
         [0057]     The image-reading device  1  can read an original having a narrow width at a time equivalent to the maximum number of pixels in image sensor IC chips for an original having a narrow width×the pixel period. Further, when reading an original having a narrow width, the image-reading device can achieve the same effects whether the original is left-justified or centered.  
         [0058]     While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.  
         [0059]     For example, the image-reading device  10  is provided with the size input unit (not shown) into which a user inputs the size of the original and the position of the original, that is, whether the original is left-justified or centered in the preferred embodiment. However, the image-reading device  10  may be provided with sensors that detect the size of the original and the position of the original instead of the size input unit.  
         [0060]     In the preferred embodiment, the switches SW 1 , SW 2  and SW 3  are switched based on whether the original is A4-size or A3-size. However, the switches SW 1 , SW 2  and SW 3  may be switched based on whether the original is letter size or double-letter size.