Abstract:
An image-reading device includes a linear image sensor and a cable. The linear image sensor is divided into, at least, first, second and third blocks. The first block is disposed adjacent to the second block. Each block reads images on an original document and generates image signals. The cable includes, at least, first, second and third signal wires corresponding to the first, second and third blocks respectively. Each signal wire transmits the image signals generated by each block. The third wire is sandwiched between the first signal wire and the second signal wire.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priorities to Japanese Patent Application Nos. 2005-191258 filed on Jun. 30, 2005, the contents of which are hereby incorporated by reference into the present application.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to an image-reading device employing an image sensor having a one-dimensional array of light-receiving elements for reading an image from an original document as electronic data.  
       BACKGROUND  
       [0003]     Image-reading devices and image-forming devices well known in the art include scanners, facsimile machines, copiers, and multifunction devices including a combination of these functions. These conventional devices use image sensors having a one-dimensional array of light-receiving elements for reading images from original documents as electronic data.  
         [0004]     One such image-reading device disclosed in Japanese unexamined patent application publication No. 2003-298813 has a plurality of sensor IC chips arranged in a linear array and provided with a plurality of built-in photodetectors. The photodetectors receive light irradiated from a light source after the light is reflected off the original document, and the sensor IC chips are configured to output image signals of a level corresponding to the amount of received light as a serial analog signal.  
         [0005]     The number of sensor IC chips is set to a natural multiple of three, and the sensor IC chips are divided into blocks of this natural multiple, with each block outputting an image signal. In this way, it is possible to provide an image reader capable of accelerating the process of reading an image and capable of reducing the cost of a device employed in processing image signals.  
         [0006]     An example configuration of the image reader described above is shown in  FIG. 8 . Here, the sensor IC chips are divided into three blocks B 1 -B 3 , each having a corresponding cable or wiring pattern C 1 -C 3  linking the blocks to a connector  18 . The connector  18  is connected to an external circuit, such as a gate array  33 , via a flexible flat cable  39 . Accordingly, image signals outputted from the blocks B 1 -B 3  of sensor IC chips are conveyed to the gate array  33  via the connector  18  and flexible flat cable  39 .  
         [0007]     With the configuration shown in  FIG. 8 , a reading unit  13  accommodating these sensor IC chips for reading images moves in a prescribed scanning direction, requiring that the flexible flat cable  39  have a length exceeding one meter so as not to restrict the reading unit  13  in its range of movement. Consequently, when reading and copying an image from a paper having the width of an A4-size sheet with blocks B 1  and B 2  of the sensor IC chips, stray capacitance, parasitic capacitance, common impedance in the ground, and other effects lead to cross talk between the adjacent wiring patterns C 1  and C 2 . Since cross talk is the leakage of unnecessary signals, image data read by the original block B 2 , indicated by a solid line in  FIG. 8 , is leaked from the wiring pattern C 2  to the wiring pattern C 1  and is superposed in the copy results for the wiring pattern C 1 , indicated by the dotted line in  FIG. 8 , as if the image were read by the block B 1 .  
         [0008]     In another method, the flexible flat cable  39  is covered with a shielded wire. However, this shielded wire increases the weight of the flexible flat cable  39  and is not very flexible, thereby hampering movement of the flexible flat cable  39  in the movable range of the reading unit  13 . Further, such shielded wire is expensive and, therefore, increases the cost of the image-reading device.  
       SUMMARY  
       [0009]     In view of the foregoing, it is an object of the present invention to provide an image-reading device capable of reducing the effects of cross talk during an image-reading operation.  
         [0010]     In order to attain the above and other objects, this invention provides an image-reading device including a linear image sensor and a cable. The linear image sensor is divided into, at least, first, second and third blocks. The first block is disposed adjacent to the second block. Each block reads images on an original document and generates image signals. The cable includes, at least, first, second and third signal wires corresponding to the first, second and third blocks respectively. Each signal wire transmits the image signals generated by each block. The third wire is sandwiched between the first signal wire and the second signal wire. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which:  
         [0012]      FIG. 1  is a perspective view of a multifunction device according to the preferred embodiment of the present invention;  
         [0013]      FIGS. 2A and 2B  are cross-sectional views of the multifunction device in  FIG. 1 ;  
         [0014]      FIG. 3  is a block diagram showing the control structure for the multifunction device;  
         [0015]      FIG. 4  is a perspective view of linear image sensors;  
         [0016]      FIG. 5  is a circuit diagram showing a detailed structure of the linear image sensors;  
         [0017]      FIG. 6  is a block diagram showing the signal flow from the linear image sensors;  
         [0018]      FIG. 7  is an explanatory diagram illustrating the structure of an image-reading device according to the present invention; and  
         [0019]      FIG. 8  is an explanatory diagram illustrating the structure of a conventional image-reading device. 
     
    
     DETAILED DESCRIPTION  
       [0020]     Next, a preferred embodiment of the image-reading device according to the present invention will be described through the example of a multifunction device having a scanner function and facsimile function. However, the image-reading device of the present invention are not limited to the multifunction device described herein, but may be applied to a scanner, a facsimile machine, a copier, a printer, or the like.  
         [0021]      FIG. 1  is a perspective view and  FIGS. 2A and 2B  are cross-sectional views of a multifunction device  1  according to the preferred embodiment of the present invention. The multifunction device  1  includes an automatic document feeder (ADF) scanning mechanism and a flatbed scanning mechanism.  
         [0022]     The ADF scanning mechanism is configured of an original-loading tray  3 , for supporting an original document to be scanned; an original guide  5  for guiding the original fed from the original-loading tray  3 ; a feeding roller  7  for feeding sheets of the original document loaded in the original-loading tray  3  along the original guide  5 ; an original discharge tray  9  for receiving the original document fed by the feeding roller  7  after the document has been scanned; a contact glass  11  disposed below the feeding roller  7  on the conveying path of the original document; and a reading unit  13 , having a light source  15 , disposed beneath the contact glass  11  for scanning an image from the original document.  
         [0023]     The flatbed scanning mechanism includes a glass flatbed original-supporting surface  19  for supporting an original document; a pressing plate  17  for pressing the document against the original-supporting surface  19 ; and the reading unit  13  and light source  15  described above.  
         [0024]     When scanning an original using the ADF scanning mechanism illustrated in  FIG. 2A , an original A is loaded on the original-loading tray  3 . When a command is given to begin scanning, the feeding roller  7  begins to rotate and feeds the original A so that the original A passes over the contact glass  11 . At this time, the reading unit  13  positioned below the contact glass  11  reads an image from the original A through the contact glass  11 .  
         [0025]     When scanning an original with the flatbed scanning mechanism illustrated in  FIG. 2B , an original B is placed on top of the original-supporting surface  19 , and the pressing plate  17  is lowered over the original B so as to press the original B against the original-supporting surface  19 . When a command is given to begin scanning, the reading unit  13  begins scanning the original B while moving together with the light source  15  in the direction indicated by the arrow in  FIG. 2B .  
         [0026]      FIG. 3  is a block diagram showing a main circuit board  28  provided inside the body of the multifunction device  1 . As shown in  FIG. 3 , the main circuit board  28  includes a CPU  30 , a RAM  31 , a ROM  32 , a gate array  33 , a network control unit (NCU)  34 , a modem  35 , an EEPROM  36 , a codec  37 , and a direct memory access controller (DMAC)  38 .  
         [0027]     The CPU  30 , RAM  31 , ROM  32 , gate array  33 , NCU  34 , modem  35 , EEPROM  36 , codec  37 , and DMAC  38  are all connected to each other via a bus line  26 . The bus line  26  includes an address bus, a data bus, and control signal lines. The gate array  33  is also connected to the reading unit  13  described above, a storage unit  22 , a control panel  23 , a display unit  24 , and an external connector  25 . The NCU  34  is connected to a telephone line  27 .  
         [0028]     The CPU  30  controls the overall operations of the multifunction device  1 . The NCU  34  connected to the telephone line  27  performs network control operations for connecting to and disconnecting from the telephone line, and the like. The RAM  31  serves as a line buffer memory that is used as a work area for the CPU  30  and an area for developing the scanned image. The modem  35  modulates and demodulates facsimile data and the like. The ROM  32  stores such data as programs executed by the CPU  30  and various settings. The EEPROM  36  stores various flags, settings, and the like. The gate array  33  functions as an input/output interface between various components, such as the CPU  30  and reading unit  13 . The codec  37  encodes and decodes facsimile data. The DMAC  38  primarily reads data from and writes data to the RAM  31 .  
         [0029]     The storage unit  22  is a laser printer or the like that functions to record images on recording paper. The control panel  23  includes various buttons that the user presses to transmit corresponding operating signals to the CPU  30 . The display unit  24  includes a liquid crystal display (LCD) and the like for displaying the operating state of the multifunction device  1  and other information. The external connector  25  functions to connect an external device, such as a personal computer, to the multifunction device  1 .  
         [0030]     The reading unit  13  includes a linear image sensor  21  having a plurality of sensor IC chips  2  (see  FIG. 4 ), and the light source  15  described above. The reading unit  13  functions to read an image from an original or other input sheet. The light source  15  includes light sources  15 R,  15 G, and  15 B for emitting light in the respective colors red, green, and blue. The light sources  15 R,  15 G, and  15 B are mounted on the surface of a substrate  14  (see  FIG. 4 ) and are aligned in a row at fixed intervals in a main scanning direction (a direction orthogonal to the surface of the drawings in  FIGS. 2A and 2B ). The light emitted from each light source is reflected off the surface of the original document being scanned and received by light-receiving elements  20  (see  FIG. 4 ) in the sensor IC chips  2 .  
         [0031]     Next, the linear image sensor  21  will be described in detail with reference to  FIGS. 4 and 5 . As shown in  FIG. 5 , each sensor IC chip  2  includes phototransistors PT 1 -PTn of a prescribed number (for example, 1,728), field effect transistors FET 1 -FETn and a shift register  29 . Each of the phototransistors PT 1 -PTn is configured of a light-receiving element  20 . Upon receiving light, the phototransistors PT 1 -PTn store an electric charge corresponding to the amount of received light. When a start pulse SP described later is inputted into the sensor IC chip  2 , the shift register  29  sequentially turns on the field effect transistors FET 1 -FETn in a fixed direction according to an inputted clock signal CLK described later. As a result, the electric charges stored in the phototransistors PT 1 -PTn are discharged in a fixed sequence. The basic circuit structure of the sensor IC chips  2  themselves is identical to the conventional sensor IC chips.  
         [0032]     A plurality of the sensor IC chips  2  is mounted on the surface of the substrate  14  in a row extending in the same direction as the row of light-receiving elements  20 . The multifunction device  1  according to the preferred embodiment is configured to support the reading of an A3-size document.  
         [0033]     As shown in  FIG. 4 , six sensor IC chips  2  ( 2   a - 2   f ) are divided into unit blocks of two sensor IC chips  2  per block, making a total of three blocks B 1  (IC chips  2   a  and  2   b ), B 2  (IC chips  2   c  and  2   d ), and B 3  (IC chips  2   e  and  2   f ) in order from one end to the other of the row. Wiring patterns C 1 -C 3  are formed on the surface of the substrate  14 , as shown in  FIG. 7 . One end of each wiring pattern leads to a connector  18  disposed on an edge of the substrate  14 . A flexible flat cable  39  connected to the connector  18  enables the supply of power to the sensor IC chips  2  from a source external to the substrate  14  and enables input and output of various signals with the sensor IC chips  2 . The other end of the flexible flat cable  39  is connected to the main circuit board  28 , and the flexible flat cable  39  has sufficient length to follow the reading unit  13  in its range of movement. The wiring patterns C 1 -C 3  are formed on the substrate  14  at positions or in a shape capable of preventing cross talk therebetween.  
         [0034]     The flexible flat cable  39  is a thin tape-like cable well known in the art having a plurality of plate-shaped conductors arranged parallel to each other and covered with polyester tape, for example.  
         [0035]     The number of blocks and the number of sensor IC chips provided per unit block are not particularly limited and are set to determine the size of sheet that can be read by the multifunction device  1  and the reading resolution of the multifunction device  1 .  
         [0036]     Of the three blocks B 1 -B 3 , two block B 1  and B 2  are used for reading an A4-size original, while all blocks B 1 -B 3  are used for reading an A3-size document.  
         [0037]     As shown in  FIG. 7 , the wiring patterns C 1 -C 3  are arranged such that the wiring pattern C 3  passes between the wiring patterns C 1  and C 2  in order to prevent cross talk from occurring between adjacent blocks B 1  and B 2 , that is, between the wiring patterns C 1  and C 2 . In other words, the wiring patterns C 1 -C 3  are arranged such that the connecting points of the wiring patterns C 1  and C 2  with the flexible flat cable  39  are not adjacent to each other. As an alternative, the flexible flat cable  39  may be directly attached to the substrate  14  instead of passing through the connector  18 .  
         [0038]     As shown in  FIG. 6 , the gate array  33  includes a control image sensor (CIS) control block  43  for supplying a start pulse SP, a clock signal CLK, and the like to the linear image sensor  21  under the overall control of the CPU  30 ; an analog front end (AFE) circuit configured of a sample hold (S/H) circuit  40 , a multiplexer  41 , and an analog/digital (A/D) converter  42 ; an AFE control block  44  for transmitting various control signals to the AFE circuit; and a memory control block  45  for sampling digital signals outputted from the A/D converter  42  and sequentially writing data based on these signals to a prescribed region in an image memory provided in the RAM  31 . The control image sensor (CIS) in the CIS control block  43  is another name for the linear image sensor  21 .  
         [0039]     The AFE control block  44  functions to transmit a clock signal S/H CLK to the S/H circuit  40  for setting a sample/hold timing; to transmit selection signals SEL 1  and SEL 2  to the multiplexer  41  for selecting which of the signals outputted from the linear image sensor  21  along the channels CH 1 -CH 3  to be inputted into the A/D converter  42 ; and to transmit a clock signal A/D CLK to the A/D converter  42  for setting the timing for analog/digital conversion.  
         [0040]     The start pulse SP is divided and inputted into the three sensor IC chips  2   a,    2   c,  and  2   e  positioned on the left in the three blocks B 1 -B 3 . As shown in  FIG. 5 , a serial out signal SO is outputted to the right sensor IC chip  2   b  of the block B 1 , for example, from a terminal P 4  on the left sensor IC chip  2   a.  This serial out signal SO is inputted as a start pulse SP to begin driving the sensor IC chip  2   b.  The sensor IC chips  2  in the other blocks B 2  and B 3  are similarly configured. After driving the sensor IC chips  2   a,    2   c,  and  2   e  positioned on the left in the respective blocks B 1 -B 3 , the right sensor IC chips  2   b,    2   d,  and  2   f  are then driven. The clock signal CLK transmitted from the gate array  33  is divided and inputted into the six sensor IC chips  2   a - 2   f.    
         [0041]     When the user operates the control panel  23  to initiate the process for reading an original, the start pulse SP outputted from the gate array  33  is inputted into a terminal P 1 , at which time the shift register  29  sequentially turns on the plurality of field effect transistors FET 1 -FETn in a fixed direction according to the clock signal CLK inputted to a terminal P 2 . As a result, 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 from a terminal P 3  as a serial image signal AO. The image signal AO is an analog signal. The sensor IC chip  2  also includes the terminal P 4  for outputting the serial out signal SO when the final image signal from the phototransistor PTn has been outputted. Further, the sensor IC chips  2  includes a terminal P 5  for supplying a voltage VDD as required power for operating the components in the sensor IC chips  2 , and a terminal P 6  connected to ground GND.  
         [0042]     When the start pulse SP is inputted into the terminal P 1  of the sensor IC chip  2   a  in the block B 1 , for example, the image signal AO is outputted from the terminal P 3  onto the channel CH 1  based on the clock signal CLK. After the FETn is turned on by the clock signal CLK, that is, after the sensor IC chip  2   a  has outputted the image signal AO, the serial out signal SO is outputted and is inputted into the sensor IC chip  2   b  as a start pulse SP. The image signal from the sensor IC chip  2   b  is also outputted on the channel CH 1 .  
         [0043]     As shown in  FIG. 6 , each analog read signal outputted from the channels CH 1 -CH 3  for the respective blocks B 1 -B 3  of the linear image sensor  21  is transmitted to the AFE circuit in the gate array  33  via the flexible flat cable  39  and is temporarily held in the S/H circuit  40  until each signal has been stabilized at a prescribed output level. Subsequently, the analog read signals are converted to digital signals based on commands from the AFE control block  44 .  
         [0044]     The multiplexer  41  has three inputs  411 ,  412 , and  413  for receiving signals on the channels CH 1 , CH 2 , and Ch 3  respectively. However, since the channels CH 1 , CH 2 , and CH 3  are arranged in the order CH 1 , CH 2 , and CH 3  on the flexible flat cable  39 , the inputs  412  and  413  cannot receive signals from the channels CH 2  and Ch 3  respectively. In the present embodiment, the wires are configured so that the signals from the channels CH 2  and CH 3  are inputted into the inputs  412  and  413  respectively after outputted from the S/H circuit  40 . In this way, when the selection signals SEL 1  and SEL 2  are inputted into the multiplexer  41  so as to turn ON the inputs  411 ,  412 , and  413  in the stated order, for example, the image signals will be inputted into the A/D converter  42  in the order CH 1 , CH 2 , and CH 3 . Therefore, this configuration prevents read image data from being stored incorrectly in the image memory, or prevents the image data from being outputted incorrectly.  
         [0045]     As an alternate method to the method described above, inputs  411 ,  412 , and  413  may receive signals from the channels CH 1 , CH 3 , and CH 2  respectively. In such a case, the selection signals SEL 1  and SEL 2  are inputted into the multiplexer  41  so as to turn ON the inputs  411 ,  412 , and  413  in the order  411  (CH 1 ),  413  (CH 2 ), and  412  (CH 3 ). In this way, the image signals can be converted to digital data by the A/D converter  42  and stored in the image memory in the correct order.  
         [0046]     Thus, the multifunction device  1  can reduce the effects of cross talk is achieved by allocating signal wires for adjacent blocks so as not to be adjacent to each other in the flexible flat cable  39 .  
         [0047]     The multifunction device  1  can also eliminate the need for shielded wire that can increase the weight and limit the movement of the flexible flat cable  39  and that can increase the cost of the multifunction device  1 .  
         [0048]     When the blocks B 1  and B 2  are used to read an A4-size image, for example, the wiring patterns C 1  and C 2  are not adjacent to each other in the flexible flat cable  39 . Accordingly, the multifunction device  1  can prevent the occurrence of cross talk.  
         [0049]     If analog signals read with a linear image sensors are converted into digital signals before outputted to a flexible flat cable, it is possible to eliminate the effects of cross talk should cross talk occur. However, this construction requires that an A/D converter is disposed near the linear image sensors, leading to a more complex circuit structure around the linear image sensors and increasing the size and weight of the section in which the linear image sensors are provided. Further, since an A/D converter is often included in a controller of an image-reading device, providing another of such circuits near the linear image sensors may lead to an increase in production costs.  
         [0050]     However, in the multifunction device  1 , the linear image sensors  21  can transmit analog image signals to the controller of the multifunction device  1  without the occurrence of cross talk. Therefore, there is no need to provide the A/D converter  42  near the linear image sensors  21 , thereby avoiding an increase in production costs.  
         [0051]     Although large-scale multifunction devices require a longer flexible flat cable that is more susceptible to the occurrence of cross talk, the multifunction device  1  can reduce the occurrence of cross talk regardless of the cable length.  
         [0052]     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.