Abstract:
An image reading apparatus reads a document on a line-by-line basis by using a reading unit. The image reading apparatus includes a modulation unit configured to modulate a clock signal at a predetermined period, a trigger signal generation unit configured to generate trigger signal for reading one line in the reading unit, a driving signal generation unit configured to generate a driving signal of the reading unit based on the clock signal output from the modulation unit and the trigger signal, and an output unit configured to change output timing of the driving signal within a range of the predetermined period each time the trigger signals are output predetermined times.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an image reading apparatus (e.g., scanner, copying machine, facsimile) which includes a control unit that operates based on a frequency-spread clock signal, and to a reading control method. 
         [0003]    2. Description of the Related Art 
         [0004]    Various types of image reading apparatus have been proposed for scanning, copying and/or faxing documents, including a type of image reading apparatus in which a document placed on a document positioning plate is scanned by a line sensor, and another type of image reading apparatus which reads the document by feeding the document to a fixed line sensor. 
         [0005]    In addition, a complementary metal-oxide semiconductor (CMOS) sensor, a charge-coupled device (CCD) sensor or the like may be used as a reading unit (reading device). Moreover, there are a number of types of light sources and methods for controlling a light source. 
         [0006]    The image reading apparatus may include a circuit board which has a control circuit and a memory and the like. The control circuit performs various image processing operations such as drive control of the reading device, capturing the image data which has been read by the reading device and the like. In addition to this circuit board, the image reading apparatus is provided with another circuit board mounting a reading sensor for scanning a document. These two circuit boards are normally connected with each other through a flexible flat cable (FFC), harness or the like. Several driving signals are necessary for driving the reading unit, and they are supplied to the reading unit via a cable. 
         [0007]    The above-mentioned image reading apparatus may not be capable of avoiding electromagnetic radiation (EMR) or electromagnetic interference (EMI) from the circuit board mounting the reading unit, a cable or the like. Further, if a faster operation of the reading unit is desired, the frequency of the driving signal in the reading unit may need to increase. As a result of increasing the operation speed of the reading unit, the level of EMR emitted from the image reading apparatus may become higher. 
         [0008]    In order to reduce the level of EMR emitted by an image reading apparatus, for example, as in the above-mentioned situation, Japanese Patent Application Laid-Open No. 2002-281252 discusses the spectrum spread clock generating circuit provided in the reference clock signal generating portion. The reference clock signal is supplied to the control circuit and the memory. The spectrum spread clock generating circuit is referred to as a Spectrum Spread Clock Generator (SSCG), for example. The above-mentioned EMR is often a higher harmonic wave, which is the multiplied reference clock signal. Accordingly, it is possible to reduce the peak level of EMR by modulating the frequency of the reference clock with the SSCG.  FIG. 8A  is a view illustrating the modulation between frequencies f L  and f H . The period of the modulation is represented by T. 
         [0009]    However, when an analog image signal obtained in the reading unit is processed based on the modulated reference clock signal, deviation in the timing due to the modulation may occur. 
         [0010]      FIG. 8B  is a view illustrating the timing at which an analog signal S 1  is sampled based on the clock signal. Sp represents a sampling signal. The frequency of a reference signal of the sampling signal Sp is also modulated. Accordingly, there is a deviation of a period ΔT between the sampling timing in the maximum frequency and that in the minimum frequency. 
         [0011]      FIG. 9A  is a view illustrating a phase relation between a timing signal of the CCD and frequency modulation in case where a reading operation is performed on a line-by-line basis by the CCD. The CCD is driven in synchronization with a signal SH which is output on a line-by-line basis. When an image is read out, a reading unit is moved at a constant speed. At this time, a signal SH is output at an interval corresponding to the moving speed. 
         [0012]    Hereinafter, for ease of explanation, the reading of four lines from nth line to (n+3)th line and the phase of the first timing signal in each line are described. f 91  represents the phase relation between the first timing signal of the nth line and the frequency modulation. The modulation phase from 0 to 180 degrees (π) is illustrated. f 92  represents the phase relation between the first timing signal of (n+1)th line and the frequency modulation. Likewise, f 93  and f 94  represent similar relations in an (n+2)th line and in an (n+3)th line, respectively. 
         [0013]    In this case, since the timing of the phase of the modulation is not controlled, a constant phase difference exists between the lines caused by the period of the signal SH and output timings of timing signals φ 1  and φ 2 . In  FIG. 9A , the phase difference of about T/4 exists between f 91  and f 92 . The phase difference of about T/4 exists also between f 92  and f 93 . As described above, the constant phase difference exists between the lines. While the first timing signal is described in this case, the second pulse and the successive pulses also have the similar relation because the timing signals φ 1  and φ 2  are output at a constant period. 
         [0014]    Therefore, even if the document having a constant density is read over a plurality of lines, pseudo streaks can be recognized when the image is displayed on a monitor. These pseudo streaks are described in a schematic diagram illustrated in  FIG. 9B . “A” represents a scanning direction, and “B” represents a direction in which the line sensor moves from a first line to an eighth line. In  FIG. 9B , streaks represented by St appear in an oblique direction. These streaks illustrate the constant phase of the clock signal between lines. 
         [0015]    In order to obscure the streaks in the read out image, according to Japanese Patent Application Laid-Open No. 2002-281252, a synchronization signal period of the main scanning is synchronized with a period of the frequency spread of the SSCG. Therefore, the SSCG is configured such that the same phase of a SSCG modulation signal is generated at a certain position from a reference point of the main scanning. In such a configuration, the positions of the streaks appearing in the image are fixed and the streaks are obscured. 
         [0016]    However, when the SSCG is configured of the analog circuit, the frequency modulation period itself is often not maintained constant, which is caused by variation in a manufacturing process and a temperature characteristic. Therefore, it is difficult to stably control the phase and period of main scanning synchronization signal and SSCG modulation signal depending on the characteristics of the SSCG. 
       SUMMARY OF THE INVENTION 
       [0017]    According to an aspect of the present invention, an embodiment is directed to an image reading apparatus for reading a document on a line-by-line basis by using a reading unit. The image reading apparatus includes, a modulation unit configured to modulate a clock signal at a predetermined period, a trigger signal generation unit configured to generate a trigger signal for reading one line in the reading unit, a driving signal generation unit configured to generate a driving signal of the reading unit based on the clock signal output from the modulation unit and the trigger signal, and an output unit configured to change output timing of the driving signal within a range of the predetermined period each time the trigger signals are output predetermined times. 
         [0018]    Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
           [0020]      FIG. 1  is a block diagram illustrating an image reading apparatus according to an exemplary embodiment of the present invention. 
           [0021]      FIG. 2  is a view illustrating a flow of a signal from a CCD sensor to an A/D converting circuit according to the exemplary embodiment of the present invention. 
           [0022]      FIG. 3  is a view illustrating timing in reading out process according to an exemplary embodiment of the present invention. 
           [0023]      FIG. 4  is a view illustrating timing in the reading out process according to a first exemplary embodiment of the present invention. 
           [0024]      FIG. 5  is a view illustrating timing in the reading out process according to a second exemplary embodiment of the present invention. 
           [0025]      FIG. 6  is a block diagram of the image reading apparatus in a third exemplary embodiment of the present invention. 
           [0026]      FIG. 7  is a view illustrating timing in the reading out process according to the third exemplary embodiment of the present invention. 
           [0027]      FIGS. 8A and 8B  are, respectively, a view illustrating modulation of frequency of a clock signal and timing of an analog signal. 
           [0028]      FIGS. 9A and 9B  are, respectively, a view illustrating timing in the conventional reading process and a schematic diagram of streaks generated by modulation. 
           [0029]      FIG. 10  is a perspective view illustrating the image reading apparatus according to an exemplary embodiment of the present invention. 
           [0030]      FIG. 11  is a cross-sectional view illustrating the image reading apparatus according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0031]    Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
         [0032]      FIG. 1  illustrates a configuration of an image reading apparatus according to the exemplary embodiments of the present invention. The image reading apparatus in  FIG. 1  reads a document by moving an image reading unit and transfers the read data to an image processing circuit  105 . After the data is processed in the image processing circuit  105 , the data is stored in a RAM  109 . A stepping motor  101  is a driving source that moves the image reading unit. A motor driving circuit  102  generates a driving signal of the stepping motor  101 , while a motor control circuit  110  controls the driving of the stepping motor  101 . 
         [0033]    The image reading unit includes a CCD (or CMOS) sensor  103  as a photoelectric conversion unit. For instance, in the case of a flatbed-type scanner, a plurality of CCD sensors  103  (line sensor) is one-dimensionally arranged, and scans along the document under a document positioning glass plate. The CCD sensor  103  inputs a signal corresponding to an optical image of the document obtained by illumination with the light source. An image resolution of the CCD sensor  103  is 300 dots per inch (dpi). When 2500 pixels are used, the width of about 211.7 mm can be read in a main scanning direction. 
         [0034]    The image signal read by the CCD sensor  103  is converted from the analog signal to a digital signal in the A/D conversion circuit  104  to be transferred to the image processing circuit  105 . The image processing circuit  105  converts the image data to a predetermined format. 
         [0035]    The image data subjected to a predetermined image processing in the image processing circuit  105  is stored in a memory, or sent to a host device through an interface such as a Universal Serial Bus (USB). 
         [0036]    Next, a control signal output from a read control circuit  106  is described. The read control circuit  106  (timing signal generating circuit) generates a control signal T 1  to be output to the CCD sensor  103 , a control signal T 2  to be output to the A/D conversion circuit  104 , and a control signal T 3  to be output to a motor control circuit  310 . These control signals T 1 , T 2  and T 3  are generated based on a modulated clock signal, which will be described below. 
         [0037]    These control signals T 1 , T 2  and T 3  are generic terms for signals that are output to each circuit. For instance, the control signal T 1  includes signals SH, φ 1 , φ 2 , and L. Meanwhile, the control signal T 2  includes a signal Sp. The control signal T 3  includes a signal Mt. 
         [0038]    The above-described read control circuit  106 , image processing circuit  105 , and motor control circuit  110  are configured as one application specific integrated circuit (ASIC). 
         [0039]    Next, the clock signal and the frequency modulation are described. In the present exemplary embodiment, a clock generator  121  (liquid crystal oscillator) generates the clock signal having a frequency of 30 MHz. A frequency spread circuit  122  (spectrum diffusion unit) generates the clock signal having a frequency of 96 MHz based on the clock signal generated by the clock generator  121 . The frequency spread circuit  122  modulates the clock signal at 94.08 MHz to 97.92 MHz. Then, the clock signal having a frequency of 94.08 MHz to 97.92 MH is output. In this case, the modulation frequency is 20 kHz. Namely, the frequency of the modulated clock signal is modulated at a period of 50 microseconds. This modulated clock signal is supplied to each integrated circuit or circuit element provided in the image reading apparatus. Also the read control circuit  106  operates based on this modulated clock signal. 
         [0040]    Next, a CPU  107  is described. The CPU  107  controls the CCD sensor  103 , the A/D conversion circuit  104 , the image processing circuit  105 , the read control circuit  106 , and the motor control circuit  110 . The CPU  107  controls them according to a control program stored in a ROM  108 , and uses a RAM  109  as a work area. 
         [0041]    In the above configuration, when a read start command is generated based on an instruction from the outside, the CPU  107  outputs the read start instruction to each circuit. The read start command is generated, for example, when a user pushes a key switch of an operating unit (not illustrated). 
         [0042]    In response thereto, the motor control circuit  110  controls the stepping motor  101  according to a predetermined speed table. The acceleration control, constant speed control, and deceleration control of the stepping motor  101  are performed by the motor control circuit  110  to move the image reading unit. In the present exemplary embodiment, a timing signal Mt for driving the stepping motor  101  by one pulse is output. 
         [0043]    When the image reading unit reaches a predetermined read start position after the moving state thereof is transferred to a constant speed region (constant speed control region), the CPU  107  causes the control circuit  106  to start the reading processing. In response to the instruction from the CPU  107 , the control circuit  106  outputs the control signal to the CCD sensor  103  and the A/D conversion circuit  104 . The image reading processing is performed until the image reading unit reaches a predetermined read finish position. 
         [0044]    When the above reading processing is performed, the image reading unit reads the image of one line (about 211 mm). If the image reading unit moves about 297 mm, a document of A4 size can be read. 
         [0045]    The read control circuit  106  generates the timing signal Mt in synchronization with a main scanning line synchronization signal SH. Therefore, the reading position in a sub scanning direction is not varied and the image can be favorably read also in the sub scanning direction. 
         [0046]      FIG. 2  is a view illustrating a flow of a signal from the CCD sensor  103  to the A/D conversion circuit  104 . The analog signal output from the CCD sensor  103  is sent to the A/D conversion circuit  104  through an amplifier  111 . 
         [0047]    The CCD sensor  103  includes a diode array (photoelectric conversion element)  103   a,  a shift register (charge transfer shift register)  103   b,  and output unit  103   c.  The shift register  103   b  is operated by two kinds of pulse signals (φ 1 , φ 2 ). As described below, these pulse signals are expressed also as CCD driving clock signals (φ 1 , φ 2 ). 
         [0048]    The transmission from the diode array  103   a  to the shift register  103   b  is performed in synchronization with the main scanning line synchronization signal SH. The diode array  103   a  accumulates electric charge of one line. The electric charge of one line is synchronized with one transfer signal, and parallel transmitted at a time to the shift register  103   b.  Thereafter, the shift register  103   b  synchronizes with the CCD driving clock signals (φ 1 , φ 2 ) to serially transmit the data to the output unit  103   c.    
         [0049]    Next, the read control circuit  106  in the image reading processing is described.  FIG. 3  is a view illustrating a relation between the timing of the pulse signals (φ 1 , φ 2 ) and the phase of the clock signal. The pulse signals (φ 1 , φ 2 ) are output in synchronization with the main scanning line synchronization signal SH. f 31  to f 34  are explanatory views similar to f 91  to f 94  described in  FIG. 9A . 
         [0050]    f 31  represents the relation between the first pulse signals (φ 1 , φ 2 ) of an nth line and the phase of the frequency modulation. f 32  represents the relation between the first pulse signals (φ 1 , φ 2 ) of an (n+1)th line and the phase of the frequency modulation. f 33  and f 34  represent similar relations. In the first pulse signals (φ 1 , φ 2 ) of each line, the relation between them and the phase is random. Therefore, the pulse signals (φ 1 , φ 2 ) of the second pulse and the successive pulses become random in each line. Accordingly, the streaks described in  FIG. 8B  are obscured. 
         [0051]    The read control circuit  106  includes a timing changing unit configured to change timing with the phase in a random manner. The read control circuit  106  changes the timing in each line. The read control circuit  106 , for example, may provide a plurality of information about delay time in a table. Instead of this method, the read control circuit  106  may be provided with a random number generating circuit. 
         [0052]    The maximum of the delay time may be a time (50 μm) equivalent to the modulation period of the frequency spread circuit  122 . Accordingly, the interval at which the main scanning line synchronization signal SH is output is determined considering this maximum of the delay time. 
       First Exemplary Embodiment 
       [0053]    The control of the image reading processing is described with reference to  FIG. 4 . The main scanning line synchronization signal SH and the motor timing signal Mt are generated in each line. In synchronization with one output of the motor timing signal Mt, the stepping motor  101  moves by one pulse. Thus, the CCD sensor  103  moves by one line each time one line is read by the CCD sensor  103 . 
         [0054]    The CCD sensor  103  operates in synchronization with the CCD driving clock signals (φ 1 , φ 2 ). The CCD driving clock signals (φ 1 , φ 2 ) correspond to the pulse signals described in  FIG. 3 . The frequency of the CCD driving clock signals (φ 1 , φ 2 ) is 3 MHz (period: 333 nsec). The CCD driving clock signals (φ 1 , φ 2 ) are output by 3000 pulses in synchronization with the main scanning line synchronization signal SH. 
         [0055]    In  FIG. 4 , the interval between the signal SH in an nth line and that in an (n+1)th line is t 1 +Δt 1 . Meanwhile, the interval between the signal SH in the (n+1)th line and that in an (n+2)th line is t 1 +Δt 1 ′. As described in  FIG. 3 , the intervals Δt 1  and Δt 1 ′ are random values to the phase of the frequency modulation. Namely, the CCD driving clock signals (φ 1 , φ 2 ) are generated in each line at timing random to the phase of the frequency modulation. The streaks described in  FIG. 8B  are obscured in the image read in the above configuration. 
       Second Exemplary Embodiment 
       [0056]    Next, the image reading processing in the second embodiment is described with reference to  FIG. 5 . The points are described which are different from the first exemplary embodiment. The description of the points similar to the first embodiment will not be repeated. 
         [0057]    As illustrated in  FIG. 5 , start timing of CCD driving clock signals (φ 1 , φ 2 ) is changed in each line. The CCD driving clock signals (φ 1 , φ 2 ) are output a period t 2  after the main scanning line synchronization signal SH is output. In the next line, the CCD driving clock signals (φ 1 , φ 2 ) are output a period t 2 +Δt 2  after the main scanning line synchronization signal SH is output. In the following line, the CCD driving clock signals (φ 1 , φ 2 ) are output a period t 2 +Δt 2 ′ after the main scanning line synchronization signal SH is output. These controls are performed by the read control circuit  106 . The periods Δt 2  and Δt 2 ′ are random values. 
       Third Exemplary Embodiment 
       [0058]    In the above embodiments, a driving source for moving the image reading unit is the stepping motor. Next, in the third embodiment, the driving source for moving the image reading unit that is a direct current (DC) motor, is described with reference to  FIG. 6 . 
         [0059]    In  FIG. 6 , the points different from the configuration of  FIG. 1  are described. The points similar to the first exemplary embodiment will not be repeated. 
         [0060]    Unlike  FIG. 1 , the motor is a DC motor  131  and includes an encoder  132 . The encoder  132 , for example, is a linear encoder, and outputs a signal (information) T 4  in response to the movement of the image reading unit in the sub scanning direction. The motor control circuit  110  controls the DC motor  131  based on the signal T 4 . In addition, the read control circuit  106  also controls the image reading unit based on the signal T 4 . 
         [0061]    The image reading processing is described with reference to  FIG. 7 . The signal T 4  is output as the reading unit moves. The main scanning line synchronization signal SH is output in synchronization with the signal T 4 . The CCD driving clock signals (φ 1 , φ 2 ) are output in synchronization with the output of the main scanning line synchronization signal SH. 
         [0062]    As illustrated in  FIG. 7 , the start timing of the CCD driving clock signals (φ 1 , φ 2 ) is changed in each line. The CCD driving clock signals (φ 1 , φ 2 ) are output a period t 2  after the main scanning line synchronization signal SH is output. In the next line, the CCD driving clock signals (φ 1 , φ 2 ) are output a period t 2 +Δt 2  after the main scanning line synchronization signal SH is output. In the following line, the CCD driving clock signals (φ 1 , φ 2 ) are output a period t 2 +Δt 2 ′ after the main scanning line synchronization signal SH is output. These controls are performed by the read control circuit  106 . The periods Δt 2  and Δt 2 ′ are random values. 
       (Image Reading Device) 
       [0063]    Next, the image reading device according to the exemplary embodiment of the present invention is described. 
         [0064]      FIG. 10  illustrates an image reading device for reading an image while a line sensor scans a document placed on a document positioning plate. 
         [0065]    The document is placed on a document platen glass  1050 . Reference numeral  1000  denotes a cover. A frame body  1010  doubles as an outer cover. A reading unit  1100  is driven by a motor  1060  to be guided by a guide shaft  1020 , and performs scanning in a direction A indicated by an arrow along the document platen glass  1050 . The reading unit  1100  is disposed on a holder  1070 . A slider  1120  is provided in the holder  1070 . Reference numerals  1040  and  1030  denote a drive wire and a pulley, respectively. Reference numeral  1080  denotes a circuit board. Reference numerals  1110  and  1130  denote flat cables. 
         [0066]      FIG. 11  is a major cross-sectional view of the image reading apparatus that reads the image by feeding the document to a fixed reading unit. As illustrated in  FIG. 11 , a document reading feeding portion  1101  has a document feeding path (hereinafter referred to as a U-turn path)  1112  of an approximately U-like shape. 
         [0067]    The U-turn path  1112  includes a separation roller  1105 , a separation pad  1104 , a document presence/absence sensor  1116 , a first feeding roller  1107  that feeds a document S, a document edge sensor  1117 , and the like. A driving source that feeds the document in this automatic paper-feeding reading apparatus is a motor (not illustrated). 
         [0068]    The document reading feeding portion  1101  includes a document placing table (document placing tray)  1114  that is connected to an upstream end side of the U-turn path  1112  and a document discharging tray  1118  at a downstream end side thereof. 
         [0069]    In  FIG. 11 , the document S is fed in a left direction, and u-turned passing through the U-turn path  1112 . Thereafter, the document S is fed in a right direction to be discharged into the document discharging tray  1118 . 
         [0070]    Meanwhile, the upstream side of the U-turn path  1112  has the separation roller  1105  and the separation pad  1104  which separate the document S picked up by a pick-up roller  1103  to one sheet. The separation roller  1105  and the separation pad  1104  are pushed against each other. The downstream side of the U-turn path  1112  has a second feeding roller  1109  that discharges the document S into the document discharging tray  1118 . 
         [0071]    A contact type image sensor  1130  disposed through the document reading feeding portion  1101  and a glass  1122  reads image information by forming the image on a sensor element while the document S is irradiated with light emitted from an LED array serving as a light source. 
       Embodiment 
       [0072]    The present invention is not limited to the numeric values used in the description of the embodiment. For instance, although in this embodiment, the start timing of the CCD driving clock signals (φ 1 , φ 2 ) is changed in each line, it may be changed in each of a plurality of lines. 
         [0073]    The image resolution in the image reading unit is not limited to 300 dpi. The resolution may be 600 dpi, 1200 dpi, or the like. 
         [0074]    In addition, the frequency of the reference clock signal is not limited to 30 MHz, and the frequency modulation is also not limited to 20 kHz. The frequency of the CCD driving clock signal is not limited to 3 MHz, either. 
         [0075]    Moreover, the configuration of the image reading apparatus is not limited to that described in the embodiment. For instance, in the present exemplary embodiment, although the motor control circuit and the read control circuit are different and independent control circuits, they may be an integrated control circuit. 
         [0076]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
         [0077]    This application claims priority from Japanese Patent Application No. 2007-048297 filed Feb. 28, 2007, which is hereby incorporated by reference herein in its entirety.