Abstract:
An image forming apparatus according to the invention includes: a sensor disposed under an original stand, on which an original is placed, to be in close contact with the original stand; a first light source that irradiates light on a scanning area of the original from a direction obliquely below the original; and a second light source that is disposed in a position opposite to the first light source across the sensor and irradiates light from a direction obliquely below the original opposite to a direction of the light irradiated from the first light source. When the original is not a stuck original, the first light is turned on and, when the original is a stuck original, the first light source and the second light source are turned on. According to the image forming apparatus according to the invention, it is possible to reduce power consumption while preventing occurrence of an original shade of a stuck original in a contact-type optical system.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an image scanning apparatus, an image forming apparatus, and an image scanning method, and, more particularly to an image scanning apparatus, an image forming apparatus, and an image scanning method that use a contact-type sensor. 
         [0003]    2. Description of the Related Art 
         [0004]    An image scanning apparatus such as a scanner and an image forming apparatus such as a copying machine include optical systems for scanning an original. The optical systems can be classified into a “reduction optical system” and a “contact optical system” (a CIS system: Contact Image Sensor). 
         [0005]    The “reduction optical system” is a system for, while returning reflected light from an original many times with a mirror, leading the reflected light to a condenser lens and reading a reflection signal from the original with a sensor provided in a position apart from the original. Compared with the “contact optical system”, the “reduction optical system” has an advantage that a large depth of field can be secured. However, since an optical path length from the original to the sensor is large, in general, a physical length of the “reduction optical system” is large. 
         [0006]    On the other hand, the “contact optical system” is a system for arranging a sensor under an original to be in contact with the original. The “contact optical system” has a disadvantage that a depth of field is small but has an advantage that a physical size thereof is small. 
         [0007]    An original obtained by partially sticking two or more originals together (hereinafter referred to as stuck original) is included in originals to be scanned by the scanner or the copying machine. Since such a stuck original has a step in a stuck portion, the portion of the step may form a shade (hereinafter referred to as original shade) and appear as a black line in image data scanned. 
         [0008]    In the case of the “reduction optical system”, since it is possible to irradiate direct light from a light source and reflected light from a mirror on the step of the stuck portion from different directions, an influence of the original shade is relatively small. 
         [0009]    On the other hand, since the “contact system optical system” is a form in which a mirror is not provided, there is a problem in that, when an original is irradiated by one light source from a direction obliquely below the original, an influence of the original shade of the stuck portion is large. 
         [0010]    In order to solve this problem, in the “contact system optical system”, a method of providing two light sources on the left and the right across a contact-type sensor and irradiating a step portion of an original from left and right two directions obliquely below the original to prevent occurrence of an original shade is considered. 
         [0011]    However, since this method is a form in which two light sources are used, there is a problem in that power consumption increases. 
       SUMMARY OF THE INVENTION 
       [0012]    The invention has been devised in view of the circumstances and it is an object of the invention to provide an image scanning apparatus and an image forming apparatus, which include contact optical systems, and an image scanning method that can reduce power consumption while preventing occurrence of an original shade of a stuck original. 
         [0013]    In order to attain the object, an image scanning apparatus according to an aspect of the invention includes: a sensor disposed under an original stand, on which an original is placed, to be in close contact with the original stand; a first light source that irradiates light on a scanning area of the original from a direction obliquely below the original; and a second light source that is disposed in a position opposite to the first light source across the sensor and irradiates light on the scanning area of the original from a direction obliquely below the original opposite to a direction of the light irradiated from the first light source. When the original is not a stuck original, the first light source is turned on and, when the original is a stuck original, the first light source and the second light source are turned on. 
         [0014]    In order to attain the object, an image forming apparatus according to another aspect of the invention includes: a scanner unit; an image processing unit that applies various kinds of image processing to image data generated by the scanner unit; and an image forming unit that prints the image data subjected to the image processing on recording paper. The scanner unit includes: a sensor disposed under an original stand, on which an original is placed, to be in close contact with the original stand; a first light source that irradiates light on a scanning area of the original from a direction obliquely below the original; and a second light source that is disposed in a position opposite to the first light source across the sensor and irradiates light on the scanning area of the original from a direction obliquely below the original opposite to a direction of the light irradiated from the first light source. When the original is not a stuck original, the first light source is turned on and, when the original is a stuck original, the first light source and the second light source are turned on. 
         [0015]    In order to attain the object, an image scanning method according to still another aspect of the invention includes the steps of: scanning an original using a sensor disposed under an original stand, on which the original is placed, to be in close contact with the original stand; irradiating light on a scanning area of the original from a direction obliquely below the original using a first light source; and irradiating light on the scanning area of the original from a direction obliquely below the original opposite to a direction of the light irradiated from the first light source using a second light source that is disposed in a position opposite to the first light source across the sensor. When the original is not a stuck original, the first light source is turned on and, when the original is a stuck original, the first light source and the second light source are turned on. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    In the accompanying drawings: 
           [0017]      FIG. 1  is a diagram showing an example of structures of an image scanning apparatus and an image forming apparatus according to an embodiment of the invention; 
           [0018]      FIG. 2  is a diagram showing an example of a structure of a CIS unit according to the embodiment; 
           [0019]      FIGS. 3A and 3B  are diagrams schematically showing a state of an original shade that occurs when a stuck original is scanned only by a main lamp; 
           [0020]      FIGS. 4A and 4B  are diagrams schematically showing a state in which occurrence of an original shade can be reduced when a stuck original is scanned by both a main lamp and an auxiliary lamp; 
           [0021]      FIG. 5  is a flowchart showing an example of an operation, in particular, a lighting control method for a main lamp and an auxiliary lamp according to a first embodiment; 
           [0022]      FIG. 6  is a flowchart showing an example of an operation, in particular, a lighting control method for a main lamp and an auxiliary lamp according to a second embodiment; 
           [0023]      FIGS. 7A and 7B  are diagrams for explaining characteristics of a stuck original used to automatically determine whether an original is a stuck original; and 
           [0024]      FIG. 8  is a diagram for explaining a lighting control method for a main lamp and an auxiliary lamp in the case in which an ADF is used. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Embodiments of an image scanning apparatus, an image forming apparatus, and an image scanning method according to the invention will be hereinafter explained with reference to the drawings. 
       (1) Structure of the Image Forming Apparatus 
       [0026]      FIG. 1  is a diagram showing an example of a structure of an image forming apparatus  1  according to an embodiment of the invention. 
         [0027]    The image forming apparatus  1  includes an image scanning apparatus  2  (a scanner unit  2 ), an image processing unit  3 , an image forming unit  4 , a paper feeding unit  5 , a paper discharging unit  6 , a control unit  7 , and an operation unit  8 . 
         [0028]    The image scanning apparatus  2  has an original glass stand  25  on which an original  100  is placed. A contact-type sensor (CIS) unit  20  is provided under the original glass stand  25  to be in close contact with the original glass stand  25 . 
         [0029]    As indicated by an arrow in the figure, the CIS unit  20  scans the original  100  while moving in a sub-scanning direction from a leading end to a trailing end of the original  100  placed on the original glass stand  25  and outputs image data scanned to the image processing unit  3 . 
         [0030]    An original bumping plate  26  is provided for positioning of the original  100  at a front end of the original glass stand  25 . A white reference plate  27  is provided below the original bumping plate  26 . The white reference plate  27  is used as a reference reflection plate in correcting non-uniformity and the like of an amount of light of a light source and sensitivity of a sensor (shading correction) with respect to a main scanning direction (a depth direction perpendicular to the sub-scanning direction). 
         [0031]    The image data outputted from the CIS unit  20  is subjected to various kinds of image processing such as shading correction, color conversion processing, space filtering processing, and tone correction processing in the image processing unit  3 . 
         [0032]    The image data subjected to the image processing is inputted to the image forming unit  4 . The image forming unit  4  exposes and develops the image data to form a toner image, for example, on a photosensitive drum (not shown) according to an electrophotographic process or the like. 
         [0033]    On the other hand, recording paper supplied from the paper feeding unit  5  is conveyed to the image forming unit  4 . In the image forming unit  4 , the toner image is transferred onto the recording paper from the photosensitive drum and fixed on the recording paper. An image is printed on the recording paper. The recording paper having the image printed thereon is discharged to the outside from the paper discharging unit  6 . 
         [0034]    The control unit  7  includes a CPU and the like and performs control for the entire image forming apparatus  1 . The operation unit  8  is connected to the control unit  7 . The operation unit  8  is also called a control panel and includes a liquid crystal display and a touch panel or various switches. 
       (2) Structure of the CIS Unit 
       [0035]      FIG. 2  is a diagram showing an example of a structure of the CIS unit  20 . The CIS unit  20  includes two exposure lamps, namely, a main lamp (a first light source)  21  and an auxiliary lamp (a second light source)  24 . 
         [0036]    The main lamp  21  includes, for example, a light guide tube extending in the main scanning direction and three LEDs of red, green, and blue provided at one end of the light guide tube. Light radiated from the LEDs is deflected while propagating through the light guide tube and uniformly irradiates the original in the main scanning direction. 
         [0037]    It is possible to output image data of R, G, and B with respect to a color original by moving the CIS unit  20  in the sub-scanning direction while sequentially switching the three LEDs of red, green, and blue. 
         [0038]    On the other hand, the auxiliary lamp  24  is, for example, a light source constituted by an LED linear array of YG (Yellow-Green). As described later, in scanning a stuck original, occurrence of an original shade of the stuck original is prevented by irradiating the original from a direction different from a direction of the main lamp  21 . 
         [0039]    The CIS unit  20  further includes a self-focusing lens  22  and a CCD sensor (a sensor)  23 . 
         [0040]    The self-focusing lens is a lens also called a selfocs lens. The self-focusing lens  22  is constituted by arranging cylindrical lens units in an array shape in the main scanning direction. 
         [0041]    The main lamp  21  and the auxiliary lamp  24  are arranged below the original glass stand (an original stand)  25  across this self-focusing lens  22 . 
         [0042]    Reflected light from an original placed on the original glass stand  25  is made incident on the self-focusing lens  22  via a glass of the original glass stand  25 , condensed on the self-focusing lens  22 , and focused on the CCD sensor  23 . 
         [0043]      FIG. 2  shows a state in which the usual original  100  (an original that is not a stuck original) is scanned. In this case, light is radiated only from the main lamp  21 . 
         [0044]    On the other hand,  FIGS. 3A and 3B  are diagrams schematically showing a state of an original shade  101  that occurs when a stuck original  100   a  is scanned. 
         [0045]    The stuck original  100   a  is, as shown in  FIG. 3A , obtained by sticking a partial original  100   b  on recording paper. This is a form frequently used, for example, when one original is created by cutting and sticking plural originals and when an original is corrected. 
         [0046]    In the stuck original  100   a , a step is formed in a portion at an edge of the partial original  100   b . Therefore, when the original is scanned only by the main lamp  21 , the step portion forms a shade to cause the original shade  101 . 
         [0047]      FIG. 3B  is a diagram schematically showing a state in which the original shade  101  occurs in a formed image as a black line on a line. 
         [0048]      FIGS. 4A and 4B  are diagrams showing a state in which the auxiliary lamp  24  is turned on in addition to the main lamp  21  in order to prevent the occurrence of such an original shade  101 . 
         [0049]    Irradiated light from the auxiliary lamp  24  is irradiated on the stuck original  100   a  from a direction obliquely below the stuck original  100   a  different from a direction of the main lamp  21  to prevent a shade from being caused by the step in the edge portion of the partial original  100   b . As a result, as shown in  FIG. 4B , it is possible to form a clear image without the original shade  101  even in the edge portion of the partial original  100   b.    
       (3) Operations (First Embodiment) 
       [0050]      FIG. 5  is a flowchart for explaining an example of operations of the image forming apparatus  1  according to this embodiment (including operations of the image scanning apparatus  2 ), in particular, operations according to lighting control for the main lamp  21  and the auxiliary lamp  24 . 
         [0051]    First, a user determines, for example, visually whether an original to be scanned by the image forming apparatus  1  is the stuck original  100   a  (step ST 1 ). 
         [0052]    When the original is the stuck original  100   a , the user operates the operation unit  8  and sets the image forming apparatus  1  in a “stuck original mode” (step ST 2 ). The “stuck original mode” set is stored in, for example, an original determining unit  70  of the control unit  7 . 
         [0053]    The user depresses a start key provided in the operation unit  8  (step ST 3 ). Scanning of the original is started under the control by the control unit  7  (step ST 4 ). 
         [0054]    The original determining unit  70  of the control unit  7  determines whether a set mode is the “stuck original mode” (step ST 5 ). When the set mode is the “stuck original mode”, the original determining unit  70  simultaneously turns on the two exposure lamps, the main lamp  21  and the auxiliary lamp  24  (step ST 7 ) and performs scanning of the original (step ST 8 ). 
         [0055]    As a result, as shown in  FIGS. 4A and 4B , it is possible to form a clear image that does not cause the original shade  101  in the stuck portion even in the stuck original  100   a.    
         [0056]    On the other hand, when the set mode is not the “stuck original mode”, the original determining unit  70  turns on only the main lamp  21  (step ST 6 ) and performs scanning of the original (step ST 8 ). 
         [0057]    When the original is not the stuck original  100   a , it is unlikely that the original shade  101  occurs. It is possible to form a clear image by turning on only the main lamp  21 . It is possible to save wasteful power consumption by turning off the auxiliary lamp  24 . 
         [0058]    When the scanning of the original ends (step ST 9 ), in the case of the “stuck original mode”, the original determining unit  70  turns off both the main lamp  21  and the auxiliary lamp  24 . When the set mode is not the “stuck original mode”, the original determining unit  70  turns off only the main lamp  21  (step ST 10 ). 
       (4) Operations (Second Embodiment) 
       [0059]    The form shown in  FIG. 5  is a form in which the user determines whether an original to be scanned is the stuck original  100   a  and operates the operation unit  8  on the basis of the determination to set a mode to the “stuck original mode”. 
         [0060]    On the other hand, a second embodiment is a form in which the image forming apparatus  1  (or the image scanning apparatus  2 ) determines whether an original to be scanned is the stuck original  100   a  and automatically sets a mode to the “stuck original mode”. 
         [0061]      FIG. 6  is a flowchart showing an example of operations of the image forming apparatus  1  (or the image scanning apparatus  2 ) according to the second embodiment. 
         [0062]    A user depresses a start key in order to start scanning of an original (step ST 11 ). 
         [0063]    In the second embodiment, first, preliminary scanning is performed according to the depression of the start key (step ST 12 ). Since the scanning is performed by turning on only the main lamp  21 , power consumption is relatively small. 
         [0064]    For example, the original determining unit  70  provided in the control unit  7  determines whether an original scanned is the stuck original  100   a  on the basis of image data obtained by the preliminary scanning (step ST 13 ). 
         [0065]      FIGS. 7A and 7B  are diagrams schematically showing characteristics of the original shade  101  that occurs when an original is the stuck original  100   a . Thickness of the partial original  100   b  stuck is usually limited to a certain range. Therefore, width W of the original shade  101  appearing in image data is usually limited to a certain range as well. 
         [0066]    In addition, it is less likely that density of the original shade  101  changes at random within the width W of the original shade. The original shade  101  has a characteristic that the density usually changes monotonously. By adopting these characteristics found in the original shape in the stuck portion as determination criteria, it is possible to determine whether the original scanned by the preliminary scanning is the stuck original  100   a.    
         [0067]    The original determining unit  70  of the control unit  7  sets the “usual mode” or the “stuck original mode” on the basis of a result of the determination (steps ST 14  and ST 15 ). 
         [0068]    In the case of the “stuck original mode” (Yes in step ST 16 ), the original determining unit  70  turns on both the main lamp  21  and the auxiliary lamp  24  (step ST 18 ). In the case of the “usual mode” (No in step ST 16 ), the original determining unit  70  turns on only the main lamp  21  (step ST 17 ). 
         [0069]    In this lighting state, the original determining unit  70  performs main scanning (step ST 19 ). When the scanning of the original ends (step ST 20 ), in the case of the “stuck original mode”, the original determining unit  70  turns off both the main lamp  21  and the auxiliary lamp  24 . When a mode is not the “stuck original mode”, the original determining unit  70  turns off only the main lamp  21  (step ST 21 ). 
         [0070]    In the second embodiment, since the preliminary scanning is required, longer time is taken for scanning. However, time and labor for visual determination of a state of an original by the user and time and labor for manual setting of the “stuck original mode” are saved. 
         [0071]    As scanning of an original, there is a form of scanning by an automatic document feeder (ADF) other than the form of placing an original on an original stand and scanning the original. 
         [0072]      FIG. 8  is a diagram schematically showing an example of an original scanning method using the ADF. Usually, a frequency of scanning the stuck original  100   a  using the ADF is not so high. 
         [0073]    However, even if a user scans the stuck original  100   a  using the ADF, as shown in  FIG. 8 , when the stuck original  100   a  is scanned by the CIS unit  20 , the stuck original  100   a  is scanned in a slightly curved state. Therefore, occurrence of the original shade  101  due to the step of the stuck portion is reduced compared with the case in which the stuck original  100   a  is placed flat on the original glass stand  25 . 
         [0074]    Thus, in this embodiment, in scanning an original using the ADF, the form of turning on only the main lamp  21  is adopted with priority given to a reduction in power consumption. Then, if the original shade  101  is conspicuous in an image formed, the form may be changed to the form of turning on both the main lamp  21  and the auxiliary lamp  24  according to operation of the operation unit  8 . 
         [0075]    The invention is not limited to the embodiments themselves. At a stage of carrying out the invention, it is possible to embody the invention by modifying the components without departing from the spirit of the invention. It is possible to form various inventions according to appropriate combinations of the plural components disclosed in the embodiments. For example, several components may be deleted from all the components disclosed in the embodiments. Moreover, the components in the different embodiments may be appropriately combined.