Abstract:
For an image-capturing unit having a light source and mirrors directing light reflected from a scanned document into a lens condensing the light onto a photoelectrically converting image sensor, a synthetic resin housing. The housing is composed of an open-ended upper frame having a top plate from which sidewalls extend, encompassing an internal space. A mounting surface for anchoring the light-source is formed on the upper side of the upper-frame top plate, and formed on the lower side of the upper-frame top plate is a pedestal on which the lens is supported. Mirror-support projections are formed on the lower side of the upper-frame top plate, or on the upper-frame sidewalls, to support the mirrors from below the lens. With this housing, the influence of heat from the light source on the optics is minimized, improving the mirrors&#39; positional accuracy.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to image-capturing units that capture image information from documents, and to image-capturing apparatus furnished with such image-capturing units. 
         [0003]    2. Description of the Related Art 
         [0004]    Recent years have seen demands for the speed at which scanners capture information to be made faster. To make the capturing speed faster while acquiring satisfactory images requires a light source with an increased quantity of light. 
         [0005]    However, the light sources, such as xenon lamps, often used for scanners generate an increased quantity of heat when providing an increased quantity of light. A consequent problem that arises is that heat from the light source deleteriously deforms the mirrors and other optical components. 
         [0006]    Furthermore, a unit frame on which the optical members are supported has been composed of a synthetic resin in order to reduce the weight of the unit frame. The unit frame has thus been integrally molded by a technique of pouring an aqueous synthetic resin into a mold. When mirrors are located below a lens as in the case of the unit shown in FIGS. 1 and 2 of Japanese Unexamined Pat. App. Pub. No. H09-66915, a fixing member for the mirrors needs to be formed below a fixing member for the lens. This complicates the shape of the mold. Moreover, if only the upper side of the frame is open and the mold needs to be removed through this opening, the direction in which the mold is removed needs to be taken into account. This further complicates the shape of the mold. In particular, the level of complexity of the shape of the mold increases with decreasing distance to the bottom the frame; that is, the level of complexity increases consistently with the distance from the opening in the unit. This reduces molding accuracy. Thus, if the mirrors are fixed to the bottom of the unit, the positional accuracy of the mirrors decreases. To solve this problem, an adjustment mechanism for the mirrors may be provided. However, this may increase the number of parts required and the number of assembly steps, sharply increasing costs. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention has been made in view of these circumstances. An object of the present invention is to provide an image-capturing unit and an image-capturing apparatus which minimize the adverse effect of heat from the light source on the optical elements and which serve to increase the positional accuracy of the optical members such as the mirrors even though the optical members are arranged at the bottom of the image-capturing unit. 
         [0008]    To accomplish the object, the present invention provides an image-capturing unit reading an image from a document, comprising a light source irradiating the document with light, a mirror group comprising a plurality of mirrors reflecting reflected light from the mirror, a final mirror reflecting the light reflected by the mirror group, a lens condensing the light incident on the lens via the final mirror, an image sensor photoelectrically converting the light condensed by the lens, a sensor board with the image sensor mounted thereon, and a synthetic resin frame with the light source, the mirror group, the lens, and the sensor board mounted thereon, wherein the frame has an upper frame having a top plate and sidewalls extending downward from the top plate and having a space inside which is surrounded by the top plate and the sidewalls and which has an open bottom, and a lower frame covering the bottom of the upper frame, wherein a light-source anchoring portion is formed on a top surface of the top plate of the upper frame so that the light source is fixed to the light-source anchoring portion, and a lens support member is formed on a bottom surface of the top plate of the upper frame to support the lens, and wherein a mirror support member is formed on the bottom surface of the top plate of the upper frame or on the sidewall to support the mirror group below the lens. 
         [0009]    According to the present invention, the heating element is fixed to the top surface (outside) of the top plate of the upper frame, and the optical member is fixed to the bottom surface (inside) of the top plate of the upper frame. The top plate thus blocks radiation heat from the light source to reduce the adverse effect of heat on the optical member. Moreover, the upper frame has the open bottom, preventing the shape of a mold from being complicated. This also allows an increase in the accuracy of the frame (mirror support section) even though the frame is located at the bottom of the image-capturing unit, resulting in the increased positional accuracy of the mirror group. The mirror group is fixed to the upper frame below the lens to form an optical path below the lens. The present invention further enables the mirror group to be easily mounted on the frame. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]      FIG. 1  is a sectional view showing an image-capturing apparatus comprising a document conveying device according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a sectional view showing a general configuration of a first reading unit; 
           [0012]      FIG. 3  is a perspective view showing an upper frame turned upside down; 
           [0013]      FIG. 4  is a perspective view of the upper frame and a lower frame; 
           [0014]      FIG. 5  is an exploded perspective view of the reading unit as viewed from a top plate; and 
           [0015]      FIG. 6  is a plan view of the assembled reading unit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    An embodiment of the present invention will be described below with reference to the drawings. 
         [0017]      FIG. 1  is a sectional view showing an image-capturing apparatus comprising a document conveying device according to an embodiment of the present invention. The image-capturing apparatus to which the present invention is applied will be described with reference to  FIG. 1 . The image-capturing apparatus H can be independently used as a scanner or connected to an image forming apparatus main body such as a printer so as to serve as a part of an MFP (Multi Function Peripheral). Reference numeral A in the figures denotes a document conveying device mounted in the image-capturing apparatus H. The document conveying device A separates a document from a set of documents on a sheet feeding tray T, conveys the sheet over a top surface of first contact glass  1  in the image-capturing apparatus H, and discharge the sheet onto a sheet discharging tray E. The document conveying device A comprises a second reading unit  4  that allows both front and back surfaces of the document to be read during a single conveying operation. 
         [0018]    The image-capturing apparatus H comprises the first contact glass (first platen glass)  1  that defines an image-capturing surface allowing the document being conveyed by the document conveying device A to be read, second contact glass (second platen glass)  2  having an area sufficient to allow the document to be loaded on the second contact glass  2 , a first reading unit  3  as an image-capturing unit that reads the document being conveyed by the image conveying device A or the sheet loaded on the second contact glass  2 , and a box-like casing  5  which supports the first and second contact glasses  1  and  2  and which accommodates the first reading unit  3 . The first reading unit  3  is supported by the casing  5  via guide means such as a guide shaft so as to be movable along the second contact glass  2  by driving means such as a motor. To read the document on the second contact glass  2 , the first reading unit  3  moves along the second contact glass  2  for reading. To read the document being conveyed by the document conveying device A, the first reading unit  3  is stopped at a position shown in  FIG. 1  for reading. 
         [0019]      FIG. 2  shows a general configuration of the first reading unit  3  in section. As shown in the figure, the first reading unit  3  comprises a lamp (light source)  6  composed of a xenon lamp or the like and shaped like an elongate bar extending in a main scanning direction (the direction of arrow X in  FIG. 3 ), and an optical system that receives reflected light from the document to propagate the received light along a predetermined optical path. Specifically, in the present embodiment, the optical system has a reflecting optical system made up of a first reflection mirror (hereinafter simply referred to as a first mirror)  7  located below the document D to receive reflected light from the document D, a second reflection mirror (hereinafter referred to as a second mirror)  8  that reflects the light from the first reflection mirror  7 , and a third reflection mirror (hereinafter referred to as a final mirror)  9  that reflects the light from the second reflection mirror  8 , as well as a condensing lens (hereinafter simply referred to as a lens)  10  that condenses the light from the final mirror  9 . The first reading unit  3  comprises a sensor unit  11  mounted at a condensing position of the lens  10  to read the document, a synthetic resin housing  12  that supports the lamp  6 , the lens  10 , the mirrors  7 ,  8 , and  9 , and the sensor unit  11 , and a reflector  18  located opposite the lamp  6  so as to provide a greater quantity of light (a higher luminance) at position where the document D is irradiated with light. In the present configuration, the optical system is incorporated in an internal space S in the housing  12  in a predetermined form described below. 
         [0020]    The first reading unit  3  comprises a shading correction plate  19  having an opening with an opening width smaller in the center thereof than in the periphery thereof so as to reduce the difference in light quantity between the center and periphery of the lens  10  to provide a uniform (flat) light quantity on a reading line. 
         [0021]    The housing  12  is composed of an upper frame  100  and a lower frame  101  each of which is integrally molded of a synthetic resin. The sensor unit  11  is composed of an image sensor  13  having a plurality of photoelectric converting elements such as a CCD to photoelectrically convert light from the document D, a sensor board  14  having the image sensor  13  mounted thereon and various circuits such as a driver circuit formed thereon to drive the image sensor  13 , and a holding member  15  that holds the sensor board  14  to adjust the position of the sensor unit  11  in order to adjust the position of the image sensor  13 . The holding member  15  has a cylindrical light shielding member  16  formed thereon to prevent external light from entering the image sensor  13 . 
         [0022]    The document D irradiated with light from the lamp  6  reflects the light (first optical path L 1 ). The light travels straight downward (a direction substantially orthogonal to an image-capturing surface) from the document and enters the reading unit  3  through an opening  17  formed in a top surface of the reading unit  3 . The light is then reflected by the first mirror  7 , located immediately below the opening  17  and below the lens  10 . The light reflected by the first mirror  7  travels to the second mirror  8 , located below and behind the lens  10  to form a second optical path L 2  between the first mirror  7  and the second mirror  8 ; the second optical path L 2  passes below the lens  10  and the sensor unit  11  and substantially parallel to the document D (image-capturing surface). Moreover, the light reflected by the second mirror  8  travels toward the final mirror  9 , located below the lamp  6  in front of (closer to an incidence surface of) the lens  10 . An optical path L 3  crossing the first optical path L 1  is formed between the second mirror  8  and the final mirror  9 . 
         [0023]    The light reflected by the final mirror  9  enters the lens  10 , is condensed by the lens  10 , and then enters the image sensor  13 , fixed to the condensing position. The final mirror  9  is located below the lens  10  and the image sensor  13 , a fourth optical path L 4  extending from the final mirror  9  through the lens  10 , into the image sensor  13  is inclined to the document D (image-capturing surface) (the final mirror  9  is located below and away from the document). That is, in the present configuration, the final mirror  9  is located in the internal space S in the housing  12  at a predetermined first position P lying opposite the second mirror  8  across the first optical path L 1 . The lens  10  is located in the in the internal space S in the housing  12  at a second position Q lying above the first position P (lying opposite the final mirror  9  across the first optical path L 1 ). 
         [0024]    The shading correction plate  19  is located closer to the incidence side of the lens  10  and below the lamp  6  to block a part of each of the third optical path L 3  and the fourth optical path L 4  for mechanical shading correction. That is, in the present embodiment, the shading correction plate  19  is positioned opposite the lens  10  across the first optical path L 1  and between the first mirror  7  and the final mirror  9  to adjust the light quantity of each of the third optical path L 3  and the fourth optical path L 4 . 
         [0025]    The image sensor  13  forms an electric signal from the incident light. An A/D converter and an image processing circuit on the sensor board  14  then execute digital signal conversion and image processing on the electric signal, which is then output to an image forming apparatus such as a printer or a personal computer via a cable or a PCB board. 
         [0026]    The mirrors  7 ,  8 , and  9 , the lens  10 , and the sensor unit  11  are thus arranged so that the fourth optical path L 4  from the final mirror  9  to the image sensor  13  is angled to the document (first contact glass  1  or second contact glass  2 ). The long optical path can thus be formed using the smaller occupying space, effectively enabling a reduction in the size of the unit. 
         [0027]    Furthermore, the lamp  6  is fixed to the position between the first optical path L 1  and the final mirror  9  (in other words, opposite the lens  10  across the first optical path L 1 ) where the corresponding part of the fourth optical path L 4  lies lower than the remaining part (the area of the housing  12  which is closer to the first position P than to the second position Q). The lamp  6  can thus be fixed to a lower position, effectively reducing the size of the unit, particularly, the thickness thereof. Furthermore, in the present embodiment, the lens  10  is fixed between the first mirror  7  and the second mirror  8 , allowing the space (free space) between the mirrors  7  and  8  to be effectively utilized as an installation space for the lens  10  to reduce the thickness of the unit. 
         [0028]    Now, the upper frame  100  will be described in detail with reference to  FIG. 3 . 
         [0029]      FIG. 3  is a perspective view showing the upper frame  100  turned upside down (the upper frame  100  is viewed from below). As shown in the figure, the upper frame  100  comprises a top plate (a support plate supporting the lamp  6  and the lens  10 )  102  located at the bottom of the figure, a first sidewall (side plate)  103  and a second sidewall (side plate)  104  formed at respective ends of the top plate  102  in the main scanning direction, shown by arrow X in the figure, and extending downward (in the figure, upward), and a third sidewall (side plate)  105  formed at an end of the top plate  102  in a sub-scanning direction shown by arrow Y in the figure and extending downward (in the figure, upward). 
         [0030]    The upper frame  100  internally has a space S′ with an open bottom which accommodates an optical system including the lens  10  and the mirrors  7 ,  8 , and  9  so that the optical system is surround by the top plate  102  and the sidewalls  103 ,  104 , and  105 ; the space S′ also forms the optical path. That is, in the present embodiment, the sidewalls  103 ,  104 , and  105  are installed upright on that surface of the top plate  102  with the lamp  6  mounted thereon which lies opposite a mounting surface  102   a  (see  FIG. 5 ) of the top plate  102 . The sidewalls  103 ,  104 , and  105  further cooperates with the top plate  102  in forming the accommodation space S′, in which the optical system is incorporated. An opening  300  is formed in the upper frame  100  opposite the top plate  102  to open the accommodation space S′. 
         [0031]    A plurality of bent portions  194  are formed on the top plate  102  in order to increase the strength of the top plate  102 . The top plate  102  has a pedestal (lens support portion)  106  formed of a synthetic resin integrally with the upper frame  100  and located in the accommodation space S′; the lens  10  is fixed to the pedestal  106 . A leaf spring  107  is fixed to the pedestal  106 , from above in the figure, with two screws  108  to fix the lens  10  to the pedestal  106 . 
         [0032]    Three projections  111  formed integrally with the sidewall  103  are arranged on a bottom surface (in the figure, a top surface) of the first sidewall  103 . Two projections  110  are formed on a bottom surface (in the figure, a top surface) of the second sidewall  104 . The projections  110  and  111  constitute a support section for the first mirror  7 . The first mirror  7  is fixed to the upper frame  100  by placing ends of the first mirror  7  on the support section and then fixing leaf springs  113  to the respective sidewalls from above with screws. 
         [0033]    Second mirror support sections  113  and  114  are formed on inner side surfaces of the top plate  102  integrally with the top plate  102  to support the second mirror  8 . The second mirror support sections  113  and  114  comprise mirror support plates  115  and  116 , respectively. As in the case of the first mirror  7 , a projection is formed on that surface of each of the mirror support plates  115  and  116  on which the second mirror  8  is supported. The second mirror  8  is fixed by placing ends of the second mirror  8  on the projections and then sandwiching the ends of the second mirror  8  and the mirror support plates  115  and  116  between channel-shaped springs  117  and  118 . 
         [0034]    An opening  200  is formed in the third sidewall  105  at a position opposite to the lens  10 . The top plate  102 , forming the opening  200 , has two projections  201  and  202 . Final mirror support plates  203 ,  203  are formed at the opposite ends of the opening  200  (only one of the final mirror support plates is shown). The final mirror  9  is fixed to the upper frame  100  by placing the final mirror  9  on the projections  201  and  202  and the support plates  203 ,  203  and then sandwiching ends of the final mirror  9  and the support plates  203 ,  203  between channel-shaped leaf springs  205  and  206 . 
         [0035]    Furthermore, as seen in  FIG. 2 , the first mirror  7  and the second mirror  8  are fixed below the lens so as to form an optical path below the lens  10 . However, the first mirror  7  and the second mirror  8  are fixed to the upper frame  100  from below as shown in  FIG. 3 , preventing the shape of the upper frame  100  from being complicated. This also prevents a mold for the upper frame  100  from being complicated, improving the accuracy of the upper frame  100  and the positional accuracy of the mirrors  7 ,  8 , and  9 . That is, the present embodiment adopts this configuration to solve a conventional problem. This will be described in detail. The housing  12 , supporting the optical system including the optical elements, is molded of a synthetic resin in order to reduce the weight as described above. However, with the synthetic resin molding, the increased level of complicatedness of shape of the interior of the housing  12  reduces the accuracy of the mold and thus the positional accuracy of the optical elements. For example, when the mirrors and the optical paths are arranged below the lens as is the case with the unit disclosed in, for example, Japanese Patent Laid-Open No. 9-69915, it is necessary to form a fixing member for the lens in the unit and to further form, below the fixing member, a passage through which the optical paths pass and a mirror support section. However, if an opening is formed only in the upper part of the unit so that the mold can be removed only from the upper part of the unit, the direction in which the mold is removed and the like need to be taken into account, complicating the shape of the mold. In particular, the number of required molds increases with decreasing distance to the bottom of the unit, that is, the number increases consistently with the distance from the opening in the unit. Of course, to solve this problem, an adjustment mechanism for the mirrors may be provided. However, this disadvantageously increases the number of parts required and the number of assembly steps, sharply increasing costs. 
         [0036]    Thus, in the present embodiment, as previously described, even though the mirror group ( 7 ,  8 , and  9 ) is fixed to the upper frame  100  below the lens  10  and the optical path is formed below the lens  10 , the bottom of the upper frame  100  is open (the opening  300 ). This prevents the shape of the mold from being complicated, increasing the accuracy of the frame (mirror support section), located at the bottom of the reading unit  3 , and thus the positional accuracy of the mirror group. Furthermore, the mirror group can be easily mounted on the frame  100 . 
         [0037]      FIG. 4  shows a perspective view of the upper frame  100  and the lower frame  101 . Also in this figure, the upper frame  100  is turned upside down. 
         [0038]    As shown in  FIG. 4 , two projections  118  and  119  are integrally formed at an end of the lower frame  101  which lies closer to the incidence surface of the lens  10  in the sub-scanning direction, shown by arrow Y. Holes  120  and  121  corresponding to the projections  118  and  119  are formed in the upper frame  100 . Furthermore, two projections (not shown) are integrally formed at an end of the lower frame  101  which lies closer to an exit surface of the lens  10  in the sub-scanning direction, shown by arrow Y. Holes (not shown) corresponding to the projections are formed in the upper frame  100 . The lower frame  101  is fixed to the upper frame  100  by inserting the projections into the holes. 
         [0039]    Positioning holes  150  are formed in the shading correction plate  19  at the opposite ends thereof in the main scanning direction. The shading correction plate  19  is positioned by aligning the holes  150  with projections formed on the upper frame  100  and is fixed by tightening screws  151 . Thus, the shading correction plate  19  is mounted on the upper frame  100  from below as is the case with the lens  10  and the mirrors  7  and  8 . 
         [0040]      FIG. 5  shows an exploded perspective view of the reading unit as viewed from the top plate  102 .  FIG. 6  shows a plan view of the assembled reading unit. As shown in these figures, the lamp  6 , the reflector  18 , and the sensor unit  11  are fixed to the top surface of the upper frame  100 , that is, the top plate  102  of the upper frame  100 . The lamp  6  is placed on the top surface (mounting surface  102   a ) of the top plate  102  of the upper frame  100 . A lamp holding member  20  is provided at the end of the lamp  6  to hold the lamp  6 . The lamp  6  is fixed to the mounting surface  102   a  of the top plate  102  via the lamp holding member  20  by tightening a screw  156  set in a hole formed in the lamp holding member  20 , into a screw hole  155  formed in the top surface of the top plate  102 . That is, in the present embodiment, the lamp  6  is located outside the housing  12 . 
         [0041]    Furthermore, holes  123  and  124  are formed in the reflector  18  at positions corresponding to positioning projections  121  and  122  formed on the top surface of the upper frame  100 . The reflector  18  is positioned by inserting the projections  121  and  122  into the holes  123  and  124  and is fixed to a predetermined position on the upper frame  100  by tightening the screws  125  and  126 . 
         [0042]    In the present embodiment, the sensor unit  11  has the holding member  15  holding the image sensor  13 . The holding member is composed of a first holding member  15   a  and a second holding member  15   b . The sensor unit  11  in the present embodiment is adjusted as described below. 
         [0043]    First, the sensor board  14  and the first holding member  15   a  are coupled together with two screws  152 . Then, a jig is used to move the first holding member  15   a  to adjust the parallelism of the image sensor  13  to a reading line. Two screws  153  are then used to combine the first holding member  15   a  and the second holding member  15   b  together. As shown in  FIG. 6 , arms  127  and  128  are formed at an end of the second holding member  15   b  in the main scanning direction, shown by arrow X and extends to the inside of the image-capturing unit  3 . Openings  129  and  130  that are elongate in the sub-scanning direction, shown by arrow Y, are formed in the arms  127  and  128 , respectively. Thus, subsequently, these arrangements and a jig are used to adjust the distance (scaling) to the image sensor  13  in the sub-scanning direction and the parallelism of the image sensor  13  to a document reading surface. After the adjustment, the screws are tightened for fixation. 
         [0044]    Furthermore, in the present embodiment, the second holding member  15   b  has a cylindrical light blocking member  16  formed so as to prevent external light from entering the image sensor  13 . The light blocking member  16  is interposed in an optical path guide member  21  formed on the top surface of the upper frame  100  and having a function of guiding light having passed through the lens  10  and blocking light. Accordingly, in the present configuration, the sensor board  14  with the image sensor  13  mounted thereon is located outside the housing  12 . 
         [0045]    As described above, in the image-capturing apparatus (first reading unit  3 ) according to the present embodiment, the lamp (light source)  6  as a heating element is located outside the housing  12 , whereas the optical system comprising the optical elements  7 ,  8 ,  9 , . . . is located inside the housing  12 . Consequently, radiation heat from the lamp  6  is blocked by the housing  12 , minimizing the adverse effect of heat on the optical system. Furthermore, in the present embodiment, as in the case of the lamp  6 , the sensor board  14  is located outside the housing  12 . Thus, heat from the image sensor  13 , acting as a heat source, is blocked by the housing  12 , inhibiting the possible adverse effect of heat from the sensor on the optical system. 
         [0046]    The present application claims priority rights from Japanese Pat. App. No. 2006-356458, which is herein incorporated by reference.