Abstract:
An image-reading device includes a plurality of image sensors, a starting signal generator and a signal timing regulator. Each image sensor reads images on a pixel basis and generating an image signal indicative of the image. The image signal is an analog signal. The starting signal generator generates starting signals at every predetermined time period. A sampling period for sampling the image signal is set within the predetermined time period. In response to the starting signal sequentially inputted to the image sensors, the image sensors read the image until the predetermined time period is expired. The signal timing regulator delays an input timing at which the starting signal is inputted to the image sensor so that the sampling periods for the plurality of image sensors are different from one another.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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. 
     2. Description of Related Art 
     Recently, time period of clock signal is used at a boundary speed at which an image sensor can read an image. 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. 
     Another conventional image-reading device disclosed in Japanese unexamined patent application publication No. HEI-7-236026 is provided with a plurality of multiplexers. The image-reading device can increase the speed for outputting data in proportion to the number of the multiplexers by outputting the data from the plurality of multiplexers. 
     The conventional image-reading device disclosed in Japanese unexamined patent application publication No. 2003-298813 is problematic in that when the image reading area increases, the number of blocks of image sensor IC chips into which the contact image sensor is divided will likely increase, thereby requiring a plurality of triple-channel AFEs. When using contact image sensors for an A3-size original, for example, the contact image sensor is divided into six blocks of image sensor IC ships, thereby requiring two triple-channel AFEs. 
     In addition, a sampling period among a single pixel reading period in which the image sensor IC ship can samples an image is one part of the single pixel reading period. Therefore, the image-reading device disclosed in Japanese unexamined patent application publication No. HEI-7-236026 is problematic in that a non-sampling period among a single pixel reading period that is not used for sampling prevents the speed for outputting data from increasing. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an image-reading device capable of achieving a fast image-reading speed with few AFEs. 
     In order to attain the above and other objects, the present invention provides an image-reading device including a plurality of image sensors, a starting signal generator and a signal timing regulator. Each image sensor reads images on a pixel basis and generates an image signal indicative of the image. The image signal is an analog signal. The starting signal generator generates starting signals at every predetermined time period. A sampling period for sampling the image signal is set within the predetermined time period. In response to the starting signal sequentially inputted to the image sensors, the image sensors read the image until the predetermined time period is expired. The signal timing regulator delays an input timing at which the starting signal is inputted to the image sensor so that the sampling periods for the plurality of image sensors are different from one another. 
     Another aspect of the present invention provides an image-reading device including a plurality of image sensors, a starting signal generator, a signal timing regulator and an A/D converter. Each image sensor reads images on a pixel basis and generates an image signal indicative of the image. The image signal is an analog signal. The starting signal generator generates starting signals at every predetermined time period. In response to the starting signal sequentially inputted to the image sensors, the image sensors read the image until the predetermined time period is expired. The signal timing regulator delays an input timing at which the starting signal is inputted to the image sensor. The A/D converter converts each image signal to digital signal after a predetermined time has elapsed since each starting signal is inputted to each image sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a perspective view of a multifunction device incorporating an image-reading device according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the image-reading device according to the first embodiment; 
         FIG. 3  is a perspective view of a contact image sensor shown in  FIG. 2 ; 
         FIG. 4  is a block diagram showing the electrical configuration of the image-reading device according to the first embodiment; 
         FIG. 5  is a circuit diagram illustrating an example structure of image sensor IC chips shown in  FIG. 4 ; 
         FIG. 6  is timing charts showing a sampling control process performed in the image-reading device according to the first embodiment; 
         FIG. 7  is a block diagram showing connections between a switching circuit and a contact image sensor in the image-reading device according to the first embodiment; 
         FIG. 8  is a block diagram showing connections between a switching circuit and a contact image sensor in an image-reading device according to a second embodiment; and 
         FIG. 9  is a block diagram showing connections between a switching circuit and a contact image sensor in an image-reading device according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A multifunction device  1  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. 
       FIG. 1  is a perspective view of a multifunction device  1  incorporating an image-reading device  10  according to the first 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. 
       FIG. 2  is a cross-sectional view of the image-reading device  10 . As shown in  FIG. 2 , 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. 
     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 . 
     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 so that the light-receiving elements  22  are moved directly below the reading position in the actual reading process. 
     As shown in  FIGS. 3 and 4 , the contact image sensor  12  is mounted on the surface of a substrate  30  and includes fifteen image sensor IC chips ch 1 -ch 15  aligned in a single row and having light-receiving elements that are also arranged linearly. Here, the expression “arranged linearly” also includes a staggered arrangement. Each of the image sensor IC chips ch 1 -ch 15  is rectangular in shape and includes a plurality of light-receiving elements spaced at intervals in a single row. 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 15  has a resolution of 1200 dpi (47.2 dot/mm) and has 936 light-receiving elements. Therefore, the contact image sensor  12  is configured of a total of 14,040 light-receiving elements arranged in a single row at equal intervals. 
     As shown in  FIG. 5 , each of the image sensor IC chips ch 1 -ch 15  includes phototransistors PT 1 -PTn that are configured of light-receiving elements (n=936 in the present embodiment). 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 15  themselves is identical to the conventional image sensor IC chips. When a trigger signal TG outputted from a clock 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 as a serial image signal AO. The image signal AO is an analog signal. The image sensor IC chips ch 1 -ch 15  also include a voltage terminal VDD through which a drive voltage as required power for operating the components in the image sensor IC chips ch 1 -ch 15  is supplied to the image sensor IC chips ch 1 -ch 15 , and a terminal GND connected to ground. 
     As shown in  FIGS. 3 and 4 , the image sensor IC chips ch 1 -ch 15  are divided into a total of five blocks B 1 -B 5  with three image sensor IC chips per block. The image sensor IC chips are arranged in a fixed order from one end to the other. 
     The image sensor IC chips ch 1 -ch 15  for the blocks B 1 -B 5  shown in  FIG. 4  have the same configuration. When the clock control circuit  41  described later transmits the trigger signal TG to a connector  31  provided on the edge of the substrate  30 , the trigger signal TG is simultaneously inputted into the image sensor IC chips ch 1 -ch 15 , driving all the image sensor IC chips ch 1 -ch 15  simultaneously. 
     As shown in  FIG. 4 , the connector  31  is provided on an edge of the substrate  30 , and a clock timing regulator circuit  32  and a switching circuit  33  are provided on the same surface of the substrate  30  as the contact image sensor  12 . The clock timing regulator circuit  32  and the switching circuit  33  are connected to the connector  31  by a wiring pattern. A device external to the substrate  30  connected to the connector  31  via a cable (not shown) can supply power and exchange signals with the image sensor IC chips ch 1 -ch 15 . 
     When the clock control circuit  41  described later inputs a clock signal CLK to the clock timing regulator circuit  32  via the connector  31 , the clock timing regulator circuit  32  outputs a first clock signal CLK 1 , second clock signal CLK 2 , third clock signal CLK 3 , fourth clock signal CLK 4 , and fifth clock signal CLK 5  to the blocks B 1 -B 5 , respectively. The clock signals are all phase-shifted with respect to each other so that a sampling period for sampling an image signal A 1  on the image sensor IC chip ch 1  of the block B 1 , a sampling period for sampling an image signal A 4  on the image sensor IC chip ch 4  of the block B 2 , a sampling period for sampling an image signal A 7  on the image sensor IC chip ch 7  of the block B 3 , a sampling period for sampling an image signal A 10  on the image sensor IC chip ch 10  of the block B 4 , and a sampling period for sampling an image signal A 13  on the image sensor IC chip ch 13  of the block B 5  do not overlap, but still all fit within a single pixel reading period. 
     As shown in  FIG. 7 , the switching circuit  33  is configured of three quintuple input switches  331 ,  332  and  333 . The first quintuple input switch  331  is connected to the image sensor IC chips ch 1 , ch 4 , ch 7 , ch 10  and ch 13 , and functions to switch the image sensor IC chips ch 1 , ch 4 , ch 7 , ch 10  and ch 13  using time-sharing to output any of the image signals A 1 , A 4 , A 7 , A 10  and A 13  as an image signal AO 1  to a single triple-channel AFE  40  described later. The second quintuple input switch  332  is connected to the image sensor IC chips ch 2 , ch 5 , ch 8 , ch 11  and ch 14 , and functions to switch the image sensor IC chips ch 2 , ch 5 , ch 8 , ch 11  and ch 14  using time-sharing to output any of the image signals A 2 , A 5 , A 8 , A 11  and A 14  as an image signal AO 2  to the single triple-channel AFE  40 . The third quintuple input switch  333  is connected to the image sensor IC chips ch 3 , ch 6 , ch 9 , ch 12  and ch 15 , and functions to switch the image sensor IC chips ch 3 , ch 6 , ch 9 , ch 12  and ch 15  using time-sharing to output any of the image signals A 3 , A 6 , A 9 , A 12  and A 15  as an image signal AO 3  to the single triple-channel AFE  40 . 
     As shown in  FIG. 4 , the image-reading device  10  includes the triple-channel AFE  40  connected to the connector  31  of the substrate  30 . The triple-channel AFE  40  is configured of the clock control circuit  41 , an analog/digital (A/D) converter  42 , a memory device  43 , and a timing control circuit  44 . 
     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 . 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. 4  merely to help distinguish them from the other lines. 
     The A/D converter  42  is a triple-channel device capable of converting three analog signals to digital signals in parallel. As shown in  FIG. 4 , the switching circuit  33  outputs the three image signals A 01 , AO 2 , and AO 3  that are inputted to the A/D converter  42  via the connector  31 . 
     The memory device  43  is configured of a random access memory (RAM), for example, and functions to store digital data of signals converted by the A/D converter  42  in association with addresses. The clock control circuit  41  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 15  are driven one at a time in order, for example. 
     The timing control circuit  44  outputs a clock timing control signal S 1  to the clock timing regulator circuit  32  and outputs a switch control signal S 2  to the switching circuit  33 . 
       FIG. 7  shows an example of connections between the contact image sensor  12  and switching circuit  33 . As described above, the contact image sensor  12  is formed of the fifteen image sensor IC chips ch 1 -ch 15 . Output terminals of all image sensor IC chip ch 1 -ch 15  are connected to the switching circuit  33 . 
     More specifically, the image sensor IC chip ch 1  is connected to a fifth input terminal of the first quintuple input switch  331 ; the image sensor IC chip ch 2  to a fifth input terminal of the second quintuple input switch  332 ; the image sensor IC chip ch 3  to a fifth input terminal of the third quintuple input switch  333 ; the image sensor IC chip ch 4  to a fourth input terminal of the first quintuple input switch  331 ; the image sensor IC chip ch 5  to a fourth input terminal of the second quintuple input switch  332 ; the image sensor IC chip ch 6  to a fourth input terminal of the third quintuple input switch  333 ; the image sensor IC chip ch 7  to a third input terminal of the first quintuple input switch  331 ; the image sensor IC chip ch 8  to a third input terminal of the second quintuple input switch  332 ; the image sensor IC chip ch 9  to a third input terminal of the third quintuple input switch  333 ; the image sensor IC chip ch 10  to a second input terminal of the first quintuple input switch  331 ; the image sensor IC chip ch 11  to a second input terminal of the second quintuple input switch  332 ; the image sensor IC chip ch 12  to a second input terminal of the third quintuple input switch  333 ; the image sensor IC chip ch 13  to a first input terminal of the first quintuple input switch  331 ; the image sensor IC chip ch 14  to a first input terminal of the second quintuple input switch  332 ; and the image sensor IC chip ch 15  to a first input terminal of the third quintuple input switch  333 . 
     An output terminal from the first quintuple input switch  331  is connected to a first input terminal of the triple-channel AFE  40 ; an output terminal from the second quintuple input switch  32  to a second input terminal of the triple-channel AFE  40 ; and an output terminal from the third quintuple input switch  33  to a third input terminal of the triple-channel AFE  40 . 
     Next, operations of the image-reading device  10  according to the first embodiment will be described. 
     First, the clock control circuit  41  of the triple-channel AFE  40  outputs the trigger signal TG. The trigger signal TG is inputted via the connector  31  into each of the image sensor IC chips ch 1 -ch 15  in the contact image sensor  12 . 
     The image signals A 1 -A 15  outputted from the respective image sensor IC chips ch 1 -ch 15  are inputted into the switching circuit  33 , while switching among five sampling periods for the image signals A 1 -A 15  during a single pixel reading period. 
     The clock timing regulator circuit  32  supplies the phase-shifted clock signals CLK 1 , CLK 2 , CLK 3 , CLK 4 , and CLK 5  to the respective blocks B 1 -B 5  of the contact image sensor  12 . The phase-shifted clock signals CLK 1 , CLK 2 , CLK 3 , CLK 4 , and CLK 5  offset the sampling periods for the sets of image signals A 1 -A 3 , A 4 -A 6 , A 7 -A 9 , A 10 -A 12 , and A 13 -A 15  in the respective blocks B 1 , B 2 , B 3 , B 4 , and B 5  so that the periods do not overlap, while ensuring that the sampling periods for the sets of signals fall within a single pixel reading period. 
     Using a method of time-sharing, the switching circuit  33  outputs three of the image signals A 1 -A 15  at a time to the triple-channel AFE  40  as image signals A 01 , AO 2 , and AO 3  while switching among the sets of image signals A 1 -A 3 , A 4 -A 6 , A 7 -A 9 , A 10 -A 12 , and A 13 -A 15  for each block. 
     The image signals A 01 , AO 2 , and AO 3  inputted into the triple-channel AFE  40  are converted into digital signals by the A/D converter  42  and stored in the memory device  43 . By not providing the triple-channel AFE  40  with an excess of input channels, it is possible to achieve efficient A/D conversion in this way. 
     Since the image-reading device  10  of the preferred embodiment has a total of fifteen image sensor IC chips ch 1 -ch 15 , and the image sensor IC chips can be divided evenly into five blocks B 1 -B 5 , each block has three image sensor IC chips. Therefore, the data lengths of image signals A 1 -A 3 , A 4 -A 6 , A 7 -A 9 , A 10 -A 12 , and A 13 -A 15  outputted from the respective blocks B 1 , B 2 , B 3 , B 4 , and B 5  are all the same, and signal processing for each set of image signals can be performed uniformly. Accordingly, this structure facilitates image processing and improves the speed of the image-reading process. 
     In the first embodiment described above, image signals A 1 -A 15  read from the five blocks B 1 -B 5  in the contact image sensor  12  are outputted while switching between sets of the image signals A 1 -A 15  in the respective blocks B 1 -B 5  in a time-sharing manner so that the sampling period for each set of image signals is phase-shifted while still falling within a single pixel reading period. Accordingly, the image-reading device of the present invention can increase the speed of the image-reading process by a value equivalent to the number of blocks× the number of image signals per block, or 5×3=15 in the present example. 
     Further, the number of blocks of image sensor IC chips will likely increase with a larger image reading area, as described above. Therefore, when considering a circuit structure employing a contact image sensor, a plurality of triple-channel AFEs has conventionally been required. For example, when using a contact image sensor for an A3-size original, it has been necessary to provide two triple-channel AFEs for six blocks. However, the image-reading device of the present invention can be configured of a single triple-channel AFE  40 . Hence, the image-reading device  10  of the present invention can be constructed simply and inexpensively. 
     [Second Embodiment] 
       FIG. 8  is a block diagram illustrating example connections between a contact image sensor  12   a  and a switching circuit  33   a  in an image-reading device  10  according to a second embodiment of the present invention. The contact image sensor  12   a  is formed of six image sensor IC chips ch 1 -ch 6  having output terminals connected to the switching circuit  33   a . Specifically, the image sensor IC chip ch 1  is connected to a second input terminal of a first dual input switch  331   a  in the switching circuit  33   a ; the image sensor IC chip ch 2  to a second input terminal of a second dual input switch  332   a ; the image sensor IC chip ch 3  to a second input terminal of a third dual input switch  333   a ; the image sensor IC chip ch 4  to a first input terminal of the first dual input switch  331   a ; the image sensor IC chip ch 5  to a first input terminal of the second dual input switch  332   a ; and the image sensor IC chip ch 6  to a first input terminal of the third dual input switch  333   a . An output terminal from the first dual input switch  331   a  in the switching circuit  33   a  is connected to the first input terminal of the triple-channel AFE  40 ; an output terminal from the second dual input switch  332   a  to the second input terminal of the triple-channel AFE  40 ; and an output terminal from the third dual input switch  333   a  to the third input terminal of the triple-channel AFE  40 . 
     The remaining components have the same structure as the image-reading device  10  according to the first embodiment shown in  FIGS. 1 through 7 . Therefore, a detailed description of these components has been omitted. 
     In the image-reading device  10  according to the second embodiment, the first, second, and third dual input switches  331   a ,  332   a  and  333   a  in the switching circuit  33   a  are switched in synchronization. In this way, image signals from the contact image sensor  12   a  configured of six image sensor IC chips ch 1 -ch 6 , which conventionally required two triple-channel AFEs  40  to process, can be processed a single triple-channel AFE  40  in the preferred embodiment. 
     [Third Embodiment] 
       FIG. 9  is a block diagram illustrating example connections between a contact image sensor  12   b  and a switching circuit  33   b  in an image-reading device  10  according to a second embodiment of the present invention. The contact image sensor  12   b  is configured of five image sensor IC chips ch 1 -ch 5  having output terminals connected to the switching circuit  33   b . Specifically, the image sensor IC chip ch 1  is connected to a second input terminal of a first dual input switch  331   b  in the switching circuit  33   b ; the image sensor IC chip ch 2  to a second input terminal of a second dual input switch  332   b ; the image sensor IC chip ch 3  to the third input terminal of the triple-channel AFE  40 ; the image sensor IC chip ch 4  to a first input terminal of the first dual input switch  331   b ; and the image sensor IC chip ch 5  to a first input terminal of the second dual input switch  332   b . An output terminal from the first dual input switch  331   b  in the switching circuit  33   b  is connected to the first input terminal of the triple-channel AFE  40 ; and an output terminal from the second dual input switch  332   b  to the second input terminal of the triple-channel AFE  40 . 
     The remaining components have the same structure as the image-reading device  10  according to the first embodiment shown in  FIGS. 1 through 6 . Therefore, a detailed description of these components has been omitted. 
     In the image-reading device  10  according to the third embodiment, the first and second dual input switches  331   b  and  332   b  in the switching circuit  33   b  are switched in synchronization. In this way, image signals from the contact image sensor  12   b  configured of five image sensor IC chips ch 1 -ch 5 , which conventionally required two triple-channel AFEs  40  to process, can be processed a single triple-channel AFE  40  in the preferred embodiment. 
     While the invention has been described in detail with reference to the specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. 
     For example, though the sampling periods are offset so as not to overlap in the above-described embodiments, the sampling periods may overlap as long as the AFE  40  can samples the image signals inputted into one channel of the AFE  40  at a different timing. 
     Though the sampling periods are regulated so as to fit within a single pixel reading period in order to raise the processing speed in the above-described embodiments, the sampling periods do not necessarily fit within a single pixel reading period. 
     Though only the clock signal CLK is regulated in the above-described embodiments, the trigger signal TG may be also regulated besides the clock signal CLK in order to ensure that the sampling periods do not overlap. 
     The sampling periods for the plurality of image sensors are regulated by delaying the switching timing of the switching circuit  33  in the above-described embodiment. However, the A/D converter  42  may simply convert each image signal outputted from the switching circuit  33  to digital signal after a predetermined time has elapsed since each clock signal CLK is inputted to each image sensor. For example, as shown in  FIG. 6 , the A/D converter  42  can convert each image signal after a predetermined time has elapsed since each clock signal CLK is inputted to each image sensor. Thus, the A/D converter  42  can convert each signal at preferable portion for sampling.