Patent Publication Number: US-8982430-B2

Title: Lighting unit and image scanner using same

Description:
TECHNICAL FIELD 
     The present invention relates to a lighting unit for accomplishing linear lighting of scanned items, such as printed material or book manuscripts, and to an image scanning device using this lighting unit. 
     BACKGROUND ART 
     Image scanning devices are used in copiers, scanners, facsimiles and/or the like. The image scanning device is a device for scanning an entire image by scanning the image in a scanning position using a one-dimensional imaging element, and is provided with a lighting unit for accomplishing lighting when reading an original. In the image scanning device, it is necessary to scan the image information with good accuracy and at high speed, so a lighting unit composition has been disclosed for uniformly lighting the original with high efficiency. As general expressions, the direction in which a one-dimensional imaging element is arrayed is called the main scanning direction, and the direction of scanning is called the sub-scanning direction. In addition, the direction orthogonal to both the main scanning direction and the sub-scanning direction is called the focal depth direction in a scanning optical system and is called the lighting depth direction in a lighting unit. 
     The document lighting unit disclosed in Patent Literature 1 is provided with point light sources such as multiple LEDs (Light Emitting Diodes) arranged in the main scanning direction. The direction in which light is emitted from these point light sources is roughly parallel to the normal direction to the document stand on which a document is loaded and is in the opposite direction from the document stand. Light from these point light sources is guided to the document surface as lighting light by multiple reflective surfaces arranged facing the point light sources. 
     The condensing lighting device disclosed in Patent Literature 2 is provided with a light source positioned at the focal position of a reflective surface on a parabola, and a lens having two types of curvature for condensing light from the light source and light from the reflective surface. 
     The document lighting device disclosed in Patent Literature 3 is provided with LED elements disposed along the main scanning direction, and a reflective plate surrounding the LED elements. The shape of this reflective plate is a parabolic two-dimensional curve. 
     Patent Literature 4 discloses the composition of a light guide, lighting unit and image-scanning lighting device capable of realizing lighting with high illumination, large lighting depth and broad lighting width in the sub-scanning direction. 
     Patent Literature 5 discloses an image scanning device in which a circuit substrate on which light-emitting diodes are provided is anchored to a metal support section, and the support section is carriage-anchored. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Unexamined Japanese Patent Application Kokai Publication No. 2010-199875 (FIGS. 1-9) 
         Patent Literature 2: Japanese Patent Official Announcement No. H4-15457 (FIGS. 1-3) 
         Patent Literature 3: Unexamined Japanese Patent Application Kokai Publication No. 2005-234108 (FIGS. 1, 2) 
         Patent Literature 4: Unexamined Japanese Patent Application Kokai Publication No. 2009-272215 (FIG. 3) 
         Patent Literature 5: Unexamined Japanese Patent Application Kokai Publication No. 2007-306309 (FIG. 4) 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the image scanning device, it is necessary to have a lighting device with a large lighting depth when utilizing a scanning optical system having a large focal depth enabling clear imaging of images of scanned objects having unevenness on the surface, such as book manuscripts or wrinkled paper money. When scanning documents having unevenness, fluctuations in the brightness of the scanned images occur when there is a brightness distribution in the lighting depth direction. 
     The document lighting unit disclosed in Patent Literature 1 comprises multiple reflective surfaces, so the angular component of the lighting light rays toward the document surface from the respective reflective surfaces with respect to the document stand has multiple peaks. As a result, it is difficult to achieve lighting with uniform illumination of a document whose distance from the document stand changes, such as a book manuscript and/or the like. 
     With the lighting device disclosed in Patent Literature 2, it is possible for the lighting light rays to approach parallel light rays as a result of a combination of parabolas and lenses, so lighting with uniform illumination is relatively easy on documents in which the distance from the document stand changes, such as book manuscripts and/or the like. However, the lighting device disclosed in this Patent Literature comprises a parabolic reflective mirror and lenses having two types of curvature, so the size of the optical system becomes large and compactness of the lighting device is difficult to realize, and cost also becomes an issue. 
     With the lighting device disclosed in Patent Literature 3, the LED elements are lined up in the main scanning direction, reflective plates surrounding the LED elements are provided and the shape of the reflective plates is a parabolic two-dimensional curve. Consequently it is possible for the lighting light rays to approach parallel light rays, so that lighting with uniform illumination is relatively easy on documents such as book manuscripts and the like whose distance from the document stand changes. However, in order to provide the reflective plates surrounding the LED elements, the optical system becomes large and making the lighting device compact becomes difficult. 
     In Patent Literature 4, a composition is disclosed in which parallel light rays are produced using a light guide. 
     In Patent Literature 5, an image scanning device is disclosed in which a circuit board on which light-emitting diodes are provided is anchored to a metal support member and the support member is carriage-anchored. In the case of this kind of composition, heat emitted by the light-emitting diodes is discharged toward the carriage via the support member, so the temperature of the carriage rises and the temperature of other electronic components provided on the carriage rises. As a result, the problem existed that deterioration of performance occurs. 
     It is an objective of the present invention to provide a high-illumination lighting unit and image scanning device that control temperature increases in the light source and/or the like caused by heat discharged from the light source while having large lighting depth. 
     Solution to Problem 
     The lighting unit according to the present invention comprises: 
     a light source in which light-emitting elements are positioned in an array in a main scanning direction; 
     a light source substrate that is a substrate extending in the main scanning direction and comprises a light-emitting element mounting section on which the light source is disposed and a non-light-emitting element mounting section extending from the light-emitting element mounting section in a direction orthogonal to the main scanning direction; 
     a parabolic mirror forming a shape in which a cylindrical paraboloid having curvature with respect to an sub-scanning direction has been clipped by an axial plane that is perpendicular to the vertex of the cylindrical paraboloid in the main scanning direction, provided with an anchoring section provided at the vertex of the cylindrical paraboloid and extending in the outside direction of the cylindrical paraboloid from the vertex, and projecting light emitted from the light source on an illumination region of an illuminated item; and 
     a heat-radiating plate extending in the main scanning direction and possessing a contact section that is in contact with the surface opposite the surface on which the light-emitting elements of the light source substrate are mounted, and a non-contact section; 
     wherein the light source is positioned so as to include the focal position of the cylindrical paraboloid in the light-emitting region of light, the central axis in the light-emitting direction of the light being perpendicular to the axial plane; and 
     the non-light-emitting element mounting section of the light source substrate is interposed between the contact section of the heat-radiating plate and the anchoring section of the parabolic mirror. 
     Advantageous Effects of Invention 
     With this invention, lighting of a document by roughly parallel light rays is possible, so it is possible to efficiently light documents. In addition, changes in the light quantity are small in the lighting depth direction, so it is possible to obtain bright images even when the distance to the document is distant. Furthermore, by positioning this kind of lighting unit on both sides of the optical axis of a scanning optical system, linear lighting having large lighting depth and uniformly strong distribution even in the sub-scanning direction is obtained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing an image scanning device according to a first preferred embodiment of the present invention; 
         FIG. 2  is a drawing showing a parabolic shape equating to the sub-scanning direction cross-sectional shape of a cylindrical parabolic mirror; 
         FIG. 3  is a light path diagram of the sub-scanning direction cross-section of the lighting unit according to the first preferred embodiment of the present invention; 
         FIG. 4  is an example of an sub-scanning direction illumination distribution according to the first preferred embodiment of the present invention; 
         FIG. 5  is a sub-scanning direction cross-section of a lighting unit according to a second preferred embodiment of the present invention; 
         FIG. 6  is a structural diagram of a white LED obtaining white light by blending secondary luminescence through yellow fluorescent material with a blue light-emitting diode as the light source, with (a) being a view from the LED light-emission direction along the central axis thereof, and (b) being a cross-sectional view taken along line A-A′ in (a) of  FIG. 6 ; 
         FIG. 7  is a sub-scanning direction cross-sectional view of a lighting unit according to a third preferred embodiment of the present invention; 
         FIG. 8  is a drawing showing the arrangement direction of an LED array according to the third preferred embodiment of the present invention; 
         FIG. 9  is an example of the sub-scanning direction illumination distribution according to the third preferred embodiment of the present invention; 
         FIG. 10  is a sub-scanning direction cross-sectional view of a lighting unit according to a fourth preferred embodiment of the present invention; 
         FIG. 11  is an example of the sub-scanning direction illumination distribution according to the fourth preferred embodiment of the present invention; 
         FIG. 12  is a cross-sectional view of a lighting unit according to a fifth preferred embodiment of the present invention; 
         FIG. 13  is a detailed view of the light rays and a cylindrical parabolic block according to the fifth preferred embodiment of the present invention; 
         FIG. 14  is a perspective view of an image scanning device according to a sixth preferred embodiment of the present invention; 
         FIG. 15  is a light path diagram of the sub-scanning direction cross-section according to the sixth preferred embodiment of the present invention; 
         FIG. 16  is a light path diagram of the sub-scanning direction cross-section according to a seventh preferred embodiment of the present invention; 
         FIG. 17  is an example of the sub-scanning direction illumination distribution according to the seventh preferred embodiment of the present invention; 
         FIG. 18  is a cross-sectional view of a lighting unit according to an eighth preferred embodiment of the present invention; 
         FIG. 19  is a sub-scanning direction cross-sectional view of a lighting unit according to a ninth preferred embodiment of the present invention; 
         FIG. 20  is a perspective view of a lighting unit according to a tenth preferred embodiment of the present invention; 
         FIG. 21  is a drawing showing the illumination distribution of the main scanning direction end according to the tenth preferred embodiment of the present invention; 
         FIG. 22  is a perspective view of an image scanning device according to an eleventh preferred embodiment of the present invention; 
         FIG. 23  is a sub-scanning direction cross-sectional view of a lighting unit according to the eleventh preferred embodiment of the present invention; 
         FIG. 24  is a sub-scanning direction cross-sectional view of a lighting unit according to a twelfth preferred embodiment of the present invention; and 
         FIG. 25  is a sub-scanning direction cross-sectional view of an image scanning device according to the twelfth preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, the preferred embodiments of the present invention are described with reference to the drawings Compositional parts that are the same or similar in each drawing are labeled with the same reference signs. 
     First Preferred Embodiment 
       FIG. 1  is a perspective view of an image scanning device according to a first preferred embodiment of the present invention. The image scanning device comprises a top glass sheet  3 , a lighting unit  2  and an imaging optical system  1 . The top glass sheet  3  is a transparent glass sheet for supporting a scanned item (illuminated item) such as a document  7  and/or the like. The lighting unit  2  is a unit for accomplishing linear lighting of a surface of the document  7 . The imaging optical system  1  is a unit for imaging light from the document  7  in an imaging element  40 . 
     To facilitate understanding, the direction of scanning the document through electrical scanning of the imaging element  40  shall be called the main scanning direction  11 , the direction in which the document  7  moves relative to the image scanning device shall be called the sub-scanning direction  12  and the direction perpendicular to the main scanning direction  11  and the sub-scanning direction  12  shall be called the depth direction  13 . Here, the depth direction  13  is such that the direction in which the document  7  is separated from the top glass sheet  3  is the positive (+) direction. 
     In this preferred embodiment, a composition is shown such that the image scanning device moves and accomplishes document scanning with the document  7  in an anchored state, but conversely, it would be fine to have a composition in which document scanning is accomplished by moving the document  7  with a drum conveyor and/or the like with the image scanning device in an anchored state. 
     The imaging optical system  1  is positioned along a light path facing from the document  7  to the imaging element  40 , and comprises a lens array and reduction optical system, and/or the like. The imaging element  40  is mounted on a substrate  4  and is a line sensor constituting a photoelectric conversion circuit for photoelectric conversion and a CMOS (Complementary Metal Oxide Semiconductor), CCD (Charge Coupled Device Image Sensor) and/or the like comprising the driver thereof. 
     The lighting unit  2  is positioned between the top glass sheet  3  and the imaging optical system  1  and accomplishes linear lighting along a scan line  8  along the x-direction to the surface of the document  7  by shining light onto the document  7  positioned on top of the top glass sheet  3 . 
     In addition, the lighting unit  2  comprises an LED array  220 , an LED substrate  230  and a cylindrical parabolic mirror  20 . The LED array  220  comprises LED chips  210  that are LED light sources, lined up linearly in the main scanning direction. The LED substrate  230  is a substrate on which the LED array  220  is mounted. The cylindrical parabolic mirror  20  is a cylindrical concave mirror that makes light emitted from the LED array  220  roughly parallel light rays and emits this lighting light toward a scan line  8 . 
     The cylindrical parabolic mirror  20  has curvature in the sub-scanning direction  12  and has no curvature in the main scanning direction  11 .  FIG. 2  shows a parabolic shape equating to the sub-scanning direction cross-sectional shape of the cylindrical parabolic mirror  20 . In  FIG. 2 , the tangential direction at the vertex  24  of the parabola, that is to say at y=0 and z=0, is taken as the y direction and the normal direction is taken as the z direction. The parabola is given by the following equation (Equation 1), where f is the focal length and y=0 and z=f is the cylindrical parabola focal position  23 . 
     
       
         
           
             
               [ 
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
               
               ] 
             
             ⁢ 
             
                 
             
           
         
       
       
         
           
             
               
                 
                   
                     z 
                     = 
                     
                       
                         cy 
                         2 
                       
                       
                         1 
                         + 
                         
                           
                             1 
                             - 
                             
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   k 
                                 
                                 ) 
                               
                               ⁢ 
                               
                                 c 
                                 2 
                               
                               ⁢ 
                               
                                 y 
                                 2 
                               
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     c 
                     = 
                     
                       1 
                       / 
                       R 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       f 
                       = 
                       
                         R 
                         / 
                         2 
                       
                     
                     , 
                     
                       k 
                       = 
                       
                         - 
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     In addition, as shown in  FIG. 2 , the cylindrical parabolic mirror  20  is formed of only a semi-cylindrical parabola y+21 when the parabola is divided at y=0 and the y+ direction is considered a semi-cylindrical parabola y+21 and the y− direction is considered a semi-cylindrical parabola y−22. Here, the z axis is called the axis of the parabola, and the surface orthogonal to the y axis and including the axis of the parabola is called the cylindrical parabola axial plane  25 . 
       FIG. 3  shows a light path diagram of the sub-scanning direction cross-section according to the first preferred embodiment of the present invention. In  FIG. 3 , the case where the lighting unit  2  is positioned to one side of an imaging optical axis  101  is shown. In order to avoid interference with the imaging optical axis  101 , the lighting unit  2  needs to be such that in general a lighting optical axis  102  is inclined from the imaging optical axis  101 . Furthermore, because there could be assembly errors in the lighting unit  2  and the imaging optical system  1 , a lighting region  104  is a region widening in the sub-scanning direction  12 , and moreover, in order to cope with book manuscripts and wrinkles in and floating of the document, when the focal depth becomes larger, the lighting region  104  broadens in the depth direction  13  as well. Consequently, in the lighting unit  2  there is a certain degree of width in the sub-scanning direction  12 , and uniform, substantially parallel light rays are necessary. Furthermore, when a certain degree of width in the sub-scanning direction  12  is secured, illumination drops and the scanning speed becomes slower, so it is necessary to improve the usage efficiency of the LED light. 
     Hence, with the first preferred embodiment of the present invention, an LED light-emission region  218  is positioned at a position including the cylindrical parabola focal position  23 . Lighting light rays  103  emitted from the cylindrical parabola focal position  23  are reflected by the cylindrical parabolic mirror  20 , become parallel light rays, pass through the top glass sheet  3  and reach the lighting region  104 . A central axis  105  in the light-emission direction of the LED is positioned in a direction perpendicular to the cylindrical parabolic mirror  24 . Because the LED&#39;s light emission intensity is at a maximum on the central axis  105  of the light-emission direction of the LED, it is possible for LED light to be efficiently incident on the cylindrical parabolic mirror  20 . 
     Accordingly, with this composition, lighting light close to parallel light is efficiently obtainable, so it is possible to efficiently light the document  7  and it is also possible to reduce changes in light amounts in the lighting depth direction. Consequently, even when the distance between the document  7  and the top glass sheet  3  is distant, it is possible to obtain a bright image. 
       FIG. 4  shows an sub-scanning direction illumination distribution according to the first preferred embodiment of the present invention.  FIG. 4(   a ) shows the sub-scanning direction illumination distribution when the lighting unit  2  is positioned to one side of the imaging optical axis  101 , as shown in  FIG. 3 . In lighting by only the lighting unit on one side, the sub-scanning direction illumination distribution is an asymmetrical distribution with respect to the sub-scanning direction  12 , and when the imaging optical axis  101  and the lighting optical axis  102  are shifted due to assembly errors and/or the like, illumination on the imaging optical axis  101  changes. In contrast,  FIG. 4(   b ) shows the sub-scanning direction illumination distribution when the lighting unit  2  is positioned on both sides of the imaging optical axis  102 . The sub-scanning direction illumination distribution becomes the sum of the lighting light from the lighting unit  2  on both sides and thus is a symmetrical illumination distribution with respect to the sub-scanning direction  12 . 
     Accordingly, with this composition it is possible to change illumination in the depth direction by setting the intersection position of optical axes of lighting units on both sides. 
     It would also be fine to set the illumination distribution of lighting units on both sides symmetrical with respect to the imaging optical axis  101 . 
     For example, when the size of the illumination region  104  is taken to be 1 mm in the sub-scanning direction and 8 mm in the depth direction, and when the inclination θ of the lighting optical axis  102  to the imaging optical axis  101  is 20°-30°, the focal length f of the cylindrical parabolic mirror  20  is appropriately around 10 mm to 20 mm. 
     Second Preferred Embodiment 
       FIG. 5  is an sub-scanning direction cross-sectional view of a lighting unit according to a second preferred embodiment of the present invention. In the second preferred embodiment of the present invention, the cylindrical parabolic mirror  20  and the LED substrate  230  are positioned using a position-determining pin  231 . Through this it is possible to accurately align the positional relationship of the cylindrical parabolic mirror  20  and the LED light-emission region  218 . As a result, the parallelism of the lighting light is maintained, it is possible to control scattering in the lighting direction and it is possible to reduce scattering of brightness in scanning. 
     Third Preferred Embodiment 
       FIG. 6  is a structural diagram of a white LED obtaining white light by blending secondary luminescence from yellow fluorescent material, with a blue light-emitting diode as the light source. The white LED is such that there are depressions in an LED package  211 , a blue light-emitting diode  212  is mounted and a yellow fluorescent material  213  is loaded so as to fill the surrounding depressions. A portion of the light emitted from the blue light-emitting diode  212  is emitted to the outside of the LED package  211  without change and becomes blue light comprising white light. In addition, the other portion of the light emitted from the blue light-emitting diode  212  is absorbed by the yellow fluorescent material and the yellow fluorescent material emits light in the region from green to red. This becomes green to red light that comprises white light. Accordingly, the blue light-emission region becomes the region of the blue light-emitting diode  212  and the red to green light-emission region becomes the entire yellow fluorescent material region. That is to say, the blue light and the red to green light have different light-emission regions. 
     In order to produce parallel light rays with less divergence using the cylindrical parabolic mirror  20 , it would be well to cause the center of the light-emission region to match the cylindrical parabola focal position  23 . However, when the light-emission regions of blue light and red to green light differ as described above, it is necessary to change the cylindrical parabola focal position  23  depending on wavelength, but realizing this kind of composition is difficult. 
     On the other hand, in observation by the inventors, it was learned that there is a yellow fluorescent material strong light-emission region surrounding the blue light-emitting diode  212 . Accordingly, it is fine to think of the green to red light-emission region as being around the blue light-emitting diode  212 , and in order to efficiently make light of all wavelengths into parallel light rays, the conclusion was reached that it would be well to make the light-emission region of the blue light-emitting diode  212  the standard. 
       FIG. 7  is an sub-scanning direction cross-sectional view of a lighting unit according to the third preferred embodiment of the present invention. When the LED chip shown in  FIG. 6  is used, it is necessary to shine light having a broad illumination depth in the sub-scanning direction  12  in the lighting region  104  in order to increase the lighting depth. Consequently, it is fine to use a light source with a broad light-emission region width, and it is fine for the direction in which LED chips  210  are arrayed in the LED array  220  to be such that the blue light-emitting diode long axis  215  matches the cylindrical parabolic mirror axial plane direction, as shown in  FIG. 8 . 
       FIG. 9  is an example of computation of the sub-scanning direction illumination distribution on the top glass sheet  3  when the center of the blue light-emitting diode  212  is caused to match the cylindrical parabolic mirror focal position  23 .  FIG. 9  ( a ) shows the sub-scanning direction distribution, while  FIG. 9  ( b ) shows the illumination change in the depth direction when the sub-scanning direction is at the center of the lighting region. By causing the blue light-emitting diode long axis  215  to match the cylindrical parabolic mirror axial plane direction, the illumination peak in the sub-scanning direction becomes relatively flat and the lighting width in the sub-scanning direction is widened. At this time, the lighting illumination 8 mm above the top glass sheet is reduced around 35% compared to the lighting illumination on (0 mm above) the top glass sheet. 
     With this kind of composition, it is possible to reduce changes in the depth direction of the sub-scanning direction illumination distribution between the blue light and the green to red light. As a result, it is possible to control color spotting. 
     Fourth Preferred Embodiment 
       FIG. 10  is an sub-scanning direction cross-sectional view of a lighting unit according to a fourth preferred embodiment of the present invention. Compared to the above-described third preferred embodiment, the fourth preferred embodiment has a composition that further controls lowering of the lighting illumination in the lighting depth direction. In  FIG. 10 , the composition is such that the cylindrical parabolic mirror focal position  23  is caused to match the side of blue light-emitting diode  212  on the cylindrical parabolic mirror vertex  24  side. 
     With this kind of composition, the light rays emitted from the side of the light-emitting diode  212  on the cylindrical parabolic mirror vertex  24  side are turned into parallel light rays by the cylindrical parabolic mirror  20  and are guided to the lighting region. On the other hand, light rays emitted from the side of the blue light-emitting diode  212  on the opposite side of the cylindrical parabolic mirror vertex  24  become light rays  106  inclined in the sub-scanning direction from the lighting optical axis  102  and are guided to the lighting region  104 . As a result, the lighting distribution in the sub-scanning direction is such that the slope on the + side in the sub-scanning direction becomes gentle, as shown in  FIG. 11(   a ). 
     Hence, the farther from the top glass sheet  3  in the depth direction, the more the peak illumination position in the sub-scanning direction distribution moves to the sub-scanning direction positive (+) direction, following the lighting optical axis angle θ. Consequently, by appropriately setting the position of the lighting unit  2  and the lighting optical axis angle θ, it is possible to cause each position in the depth direction on the imaging optical axis  101 , as shown in  FIG. 11  ( a ), and illumination at 0 mm, 4 mm and 8 mm in  FIG. 11  ( a ), to match. As a result, it is possible to make the lighting illumination at 8 mm above the top glass sheet to be virtually equal compared to the lighting illumination on (0 mm above) the top glass sheet, as shown in  FIG. 11  ( b ). 
     Accordingly, with this composition it is possible to asymmetrically dim the lighting illumination depth in the sub-scanning direction, so it is possible to further reduce the amount of change in the lighting illumination distribution in the sub-scanning direction of the depth direction of the blue light and the green to red light caused by the fact that the light-emission regions differ. 
     Fifth Preferred Embodiment 
       FIG. 12  is a cross-sectional view of a lighting unit according to a fifth preferred embodiment of the present invention. The lighting unit according to this fifth preferred embodiment of the present invention uses as the cylindrical parabolic mirror a cylindrical parabolic block  30  that is a real block formed of transparent resin. Similar to the first preferred embodiment, the cylindrical parabola focal position  23  is in the LED light-emission region  218 . Light discharged from the LED chips  210  is incident from the cylindrical parabolic block incident surface  31  to the cylindrical parabolic block  30  toward the cylindrical parabolic mirror  20 , is reflected by the inner surface of the cylindrical parabolic mirror  20  and is shined on the lighting region  104  from the cylindrical parabolic block exit surface  32  as substantially parallel light rays. 
       FIG. 13  shows a detailed view of the light rays and the cylindrical parabolic block  30 . Consider the case in which the cylindrical parabolic block incident surface  31  is parallel to the cylindrical parabola axial plane  25  and is positioned orthogonal to the central axis  105  of the LED chips  210  in the light-emission direction. The cylindrical parabolic block  30  is formed of resin and/or the like and thus has a refractive index higher than air. Consequently, light emitted from the LED light-emission region  218  when incident on the cylindrical parabolic block  30  is refracted in the direction of the central axis  105  in the light-emission direction of the LED chips  210  by the cylindrical parabolic block incident surface  31 . As a result, the divergence angle of the cylindrical parabolic block  30  becomes narrower, arriving at the cylindrical parabolic mirror  20 . 
     Accordingly, more light rays reach the cylindrical parabolic mirror  20  than the cylindrical parabolic mirror  20  positioned in the air shown in  FIG. 5  and are reflected as substantially parallel light rays, making it possible to more efficiently use LED light. Furthermore, the cylindrical parabolic block exit surface  32  is formed in a prism shape comprising a surface substantially orthogonal to and a surface substantially parallel to the light rays reflected by the cylindrical parabolic mirror  20 , so it is possible to emit light rays without changing the angle of light rays reflected by the cylindrical parabolic mirror  20 . 
     Sixth Preferred Embodiment 
       FIG. 14  is a perspective view of an image scanning device according to a sixth preferred embodiment of the present invention. The image scanning device comprises a top glass sheet  3 , a lighting unit  2  and an imaging optical system  1 . The top glass sheet  3  is a transparent glass plate for supporting an object being scanned, such as a document  7 . The lighting unit  2  is a unit for accomplishing linear lighting of the surface of the document  7 . The imaging optical system  1  is a unit for imaging light from the document  7  onto an imaging element  40 . 
     In this preferred embodiment, the lighting unit  2  comprises an LED array  220 , an LED substrate  230 , a light guide plate  400  and a cylindrical parabolic mirror  20 . The LED array  220  comprises LED chips  210  that are LED light sources lined up linearly in the main scanning direction. The LED substrate  230  is a substrate on which LED array  220  is mounted. The light guide plate  400  guides light emitted from the LED array  220  to the cylindrical parabolic mirror  20 . The cylindrical parabolic mirror  20  is a cylindrical concave mirror for turning light emitted from the light guide plate  400 , that is to say light emitted from the LED chips  210  via the light guide plate  400 , into substantially parallel light rays and shining the lighting light on a scan line  8 . 
       FIG. 15  is a light path diagram of the sub-scanning direction cross-section according to the sixth preferred embodiment of the present invention. The LED light-emission region  218  is positioned adjacent to the light guide plate incident surface  40  that is one side end of the light guide plate  400 . The light guide plate  400  is a parallel planar substrate composed of plate-shaped transparent material extending in the main scanning direction, and the surface opposite the surface adjacent to the LED chips  210 , in other words the light guide exit surface  402 , is positioned at a position including the cylindrical parabola focal position  23 . The lighting light rays  103  emitted from the light guide plate exit surface  402  near the cylindrical parabola focal position  23  are reflected by the cylindrical parabolic mirror  20 , pass through the top glass sheet  3  as substantially parallel light rays and reach the lighting region  104 . Here, it is necessary for the lighting unit  2  to be such that in general the lighting optical axis  102  is inclined from the imaging optical axis  101 , in order to prevent interference with the imaging optical axis  101 . Furthermore, because of assembly errors in the lighting unit  2  and the imaging optical system  1 , the lighting region  104  is a region spreading out in the sub-scanning direction  12 , and moreover in order to cope with book manuscripts and wrinkles in and floating of the document, when the focal depth becomes larger, the lighting region  104  widens in the depth direction  13  also. Consequently, with the lighting unit  2  there is a certain degree of width in the sub-scanning direction  12  and uniform, substantially parallel light rays are necessary. 
     Here, with the lighting unit  2  in the sixth preferred embodiment it is possible to set the lighting width in the sub-scanning direction  12  by combining the width of the light guide plate exit surface  402  in the cylindrical parabolic mirror axial plane direction in addition to the inclination θ of the imaging optical axis  101  to the lighting optical axis  102  and the focal length of the cylindrical parabolic mirror  20 . In the first through fifth preferred embodiments, the size of the light-emission region of the LED was directly related to the lighting width in the sub-scanning direction  12 , but in this sixth preferred embodiment, it is possible to set the lighting width in the sub-scanning direction without relation to the size of the light-emission region of the LED. That is to say, in a white LED obtaining white light by blending secondary light emission from a yellow fluorescent material having a blue light-emitting diode as a light source, even when the light-emission regions differ between the blue light and the green to red light, by using the light guide plate  400  it is possible to accomplish uniformity in directionality and it is possible to make the lighting widths in the sub-scanning direction match. Accordingly, it is possible to have the same amount of change in the blue light and the green to red light even with respect to the change in illumination in the depth direction. 
     Accordingly, with this composition lighting light that is nearly parallel light is obtainable. Through this, it is possible to efficiently light the document and it is possible to obtain a bright image even when the distance from the document is separated, because the light amount change is small in the depth direction of the imaging optical system. Furthermore, when the LED light source is a white LED that obtains white light by blending secondary light from a yellow fluorescent material with a blue light-emitting diode as the light source, because the light-emission regions differ, differences arise in directionality between the blue light and the green to red light, but through the light guide plate  400 , it is possible to accomplish uniformity in directionality. Through this, it is possible to make the amount by which the illumination distribution in the sub-scanning direction changes in the depth direction the same regardless of the color of light. 
     The LED substrate  230  and light guide plate  400  are respectively anchored to the cylindrical parabolic mirror  20  by a position-determining pin  231  and a light guide plate supporter  405 , and the positional relationship thereof is maintained. 
     Seventh Preferred Embodiment 
       FIG. 16  is a light path diagram of the sub-scanning direction cross-section according to a seventh preferred embodiment of the present invention. In this seventh preferred embodiment, a scatterer  410  is disposed covering the light guide plate exit surface  402 , adjacent to the light guide plate exit surface  402 . Here, the scatterer  410  has a thin plate shape and embossing or bead application processing is implemented on a sheet surface made of resin and/or the like. In addition, as the scatterer  410 , it would be fine to utilize one in which direct embossing or bead application processing has been done on the light guide plate exit surface  402 . 
       FIG. 17  is an example of the sub-scanning direction illumination distribution (a) and the illumination change in the depth direction (b) when there is no scatterer  410  and the light guide distance of the light guide plate  400  (the distance between the incident surface and exit surface) is short. With the light guide plate  400 , light emitted from the LED chips  410  is reflected by a light guide surface  403 , and standardization of directionality of the emitted light and uniformity of the light intensity at the light guide exit surface are accomplished with multiple reflections. When the light guide distance is short, the number of reflections by the light guide surface  403  is small and light emitted from the light guide has a directional distribution in accordance with the number of reflections. As a result, the sub-scanning direction illumination distribution becomes a wavy distribution in accordance with the above-described number of reflections in the sub-scanning direction, as shown in  FIG. 17  ( a ), and the lighting light proceeds in the depth direction  13  while gradually widening in the sub-scanning direction  12 . Consequently, the change in illumination in the depth direction  13  at a position 0 mm in the sub-scanning direction has wavy changes, as shown in  FIG. 17  ( b ). Consequently, the lighting illumination achieves non-monotone change even with white paper documents whose distance from the document surface to the top glass sheet  3  changes continuously. As a result, a shading distribution occurs in the scanned image. 
     With the seventh preferred embodiment, because the scatterer  410  is positioned covering the light guide plate exit surface  402 , adjacent to the light guide plate exit surface  402 , the directional distribution of the light guide exit light is eased or is converted into a substantially even scattering distribution by the scatterer  410 . Consequently, light that has passed through the scatterer  410  has a smooth directionality distribution. As shown in  FIG. 17(   c ), the sub-scanning direction illumination distribution is no longer a wavy distribution, and as a result, monotone illumination changes occur in the depth direction, as shown in  FIG. 17(   d ). Through this, it is possible to scan with a monotone density change white paper documents in which the distance from the top glass sheet  3  to the document surface continuously changes. If there is this kind of monotone density change in the depth direction, it is possible to reproduce the original density distribution of the document with simple corrections. 
     Eighth Preferred Embodiment 
       FIG. 18  is a cross-sectional view of a lighting unit according to an eighth preferred embodiment of the present invention. With the lighting unit according to the eighth preferred embodiment of the present invention, a cylindrical parabolic block  30 , which is a solid block in which a cylindrical parabolic mirror  20  is made of transparent resin, and a light guide plate  400  are formed as a single body. Similar to the eighth preferred embodiment, the cylindrical parabola focal position  23  is at the exit surface  402  of the light guide plate  400 . Hence, the light guide exit surface  400  is equivalent to the joining position of the light guide plate  400  and the cylindrical parabolic block  30 . Because the cylindrical parabolic block  30  and the light guide plate  400  are formed as a single body as described above, the light guide exit surface  402  does not exist as a physical surface. Light emitted from the LED chip  210  is incident on the light guide plate  400 , passes through the light guide exit surface  402  toward the cylindrical parabolic mirror  20  and is incident on the cylindrical parabolic block  30 . Light rays internally reflected by the cylindrical parabolic mirror  20  are projected onto the lighting region  104  from the cylindrical parabolic block exit surface  32  as substantially parallel light rays. 
     It is possible to emit light rays without changing the angle of the light rays reflected by the cylindrical parabolic mirror  20  by forming the cylindrical parabolic block exit surface  32  into a prism shape comprising a surface substantially parallel to and a surface substantially orthogonal to the light rays reflected by the cylindrical parabolic mirror  20 . 
     Accordingly, with this composition, positioning the emission exit positions of the light guide plate and the parabolic mirror is possible by integrated formation, and it is possible to eliminate variances caused by assembly. 
     Ninth Preferred Embodiment 
       FIG. 19  is an sub-scanning direction cross-sectional view of a lighting unit according to a ninth preferred embodiment of the present invention. In the ninth preferred embodiment of the present invention, an LED substrate  230  comprises a reflective sheet  232  that is all or a portion of the region in which LED chips  210  are not mounted on the surface in which the LED chips  210  are mounted. Through this composition, it is possible to guide a portion of the light hitting the LED substrate  230  to the lighting region  104 , such as lighting light rays  106  from the LED light-emission region not at the focal position of the cylindrical parabolic mirror  20 , out of light emitted from the LED chips  210 , so it is possible to efficiently light a document. 
     Here, it would be fine for the reflective sheet  232  to reflect the wavelength of light emitted from the LED chips  210 , and it is possible to use a metal plate such as an aluminum plate and/or the like, or a resin scattering sheet and/or the like. When a metal plate such as an aluminum plate and/or the like is used, it is possible for this to also be used as a heat-radiating body that dissipates heat generated from the LED chips  210 . 
     Tenth Preferred Embodiment 
       FIG. 20  is a perspective view of a lighting unit according to a tenth preferred embodiment of the present invention. The lighting unit according to the tenth preferred embodiment is provided with a reflective mirror  300  at both ends of the cylindrical parabolic mirror  20  in the main scanning direction. The cylindrical parabolic mirror  20  does not have curvature in the main scanning direction. Consequently, when there is no reflective minor  300 , the portion of the light rays emitted from the LED array  220  in the main scanning direction progresses without refracting, and progresses to the outside of the lighting unit  2  from the end surfaces of the cylindrical parabolic mirror  20  in the main scanning direction. As a result, these light rays reach the outside of the scan line  8  of the document  7  (see  FIG. 1 ) in the main scanning direction and are not effectively utilized as lighting light. Hence, by providing the reflective mirror  300 , light progressing to the outside of the cylindrical parabolic mirror  20  in the main scanning direction is reflected and through this it is possible to effectively utilize the light as lighting light by returning a portion of the light to the scan line  8  of the document  7 . 
       FIG. 21  is a drawing showing the illumination distribution at the main scanning direction end according to the tenth preferred embodiment of the present invention. In this drawing, the horizontal axis is the main scanning direction and shows the positions of the LED  210   a  of the corresponding LED array  220  and the end LED  210   b  positioned at the main scanning direction end. When there is no reflective minor  300 , because a large amount of light leaks to the outside from the end LED  210   b , illumination in the main scanning direction decreases toward the end to the inside of the end LED  210   b . On the other hand, when there is a reflective mirror  300 , it is possible to increase the lighting light amount at the main scanning direction end by reflecting light progressing to the outside in the main scanning direction. As a result, by providing the reflective mirror  300 , it is possible to lengthen the region where the main scanning direction illumination is constant to close to the end LED  210   b.    
     Accordingly, through this composition it is possible to increase the lighting light amount of the main scanning direction end, and thus it is possible to effectively shorten the length of the lighting unit in the main scanning direction. 
     Eleventh Preferred Embodiment 
       FIG. 22  is a perspective view of an image scanning device according to an eleventh preferred embodiment of the present invention. In addition,  FIG. 23  is an sub-scanning direction cross-sectional view of a lighting unit according to the eleventh preferred embodiment of the present invention. The image scanning device according to the eleventh preferred embodiment of the present invention is the lighting unit of the first preferred embodiment of the present invention, provided with heat-radiating plates. With this preferred embodiment, plate-shaped heat-radiating plates  50  formed of metal such as aluminum on the opposite surface as the mounting surface of the LED chips  210  of the LED array  230  are positioned adhered to the LED substrate, as shown in  FIGS. 22 and 23 . In addition, the cylindrical parabolic mirror  20 , the LED substrate  230  and the heat-radiating plates  50  are joined into one body by joining screws  51 . 
     As shown in  FIG. 22 , the image scanning device according to the eleventh preferred embodiment comprises imaging optical system position-determining protrusions  1   a , lighting system position-determining protrusions  50   a , imaging optical system position-determining holes  52   a  and lighting system position-determining holes  52   b . The imaging optical system position-determining protrusions  1   a  are provided in the imaging optical system  1 . The lighting system position-determining protrusions  50   a  are provided in the heat-radiating plates  50 . The imaging optical system position-determining holes  52   a  and the lighting system position-determining holes  52   b  are provided in structural support plates  52 . The imaging optical system position-determining protrusions  1   a  interlock into the imaging optical system position-determining holes  52   a , and the lighting system position-determining protrusions  50   a  interlock into the lighting system position-determining holes  52   b . Through this, the imaging optical system  1  and the lighting unit  2  are anchored. 
     The heat-radiating plates  50  are adhered and attached to the LED substrate  230  on the surface opposite the mounting surface of the LED chips  210  of the LED substrate  230 . Through this, heat generated by the LED chips  210  is efficiently discharged to the heat-radiating plates  50  and increases in the temperature of the LED chips  210  are controlled. As a result, stable operation of the lighting unit and the image scanning device becomes possible. 
     In addition, only a portion of the heat-radiating plates  50  abuts the housing and half is separated from the housing, so that heat from the LED chips  210  does not reach the housing. Accordingly, light receptors provided in the bottom of the housing do not experience an increase in temperature, so it is possible for the light receptors to receive image information from the document  7  with good sensitivity. 
     It would be fine for the heat-radiating plates  50  of the eleventh preferred embodiment of the present invention to be provided in the lighting unit  2  of each of the second through tenth preferred embodiments of the present invention. Through this, similar efficacy is obtained. 
     Twelfth Preferred Embodiment 
       FIGS. 24 and 25  are respectively sub-scanning direction cross-sectional views of a lighting unit and an image scanning device provided with such a lighting unit according to a twelfth preferred embodiment of the present invention. The image scanning device according to the twelfth preferred embodiment comprises a top glass sheet  3 , a lighting unit  2 , first lens mirrors  507 , flat mirrors  508 , apertures  509 , openings  510 , second lens mirrors  511 , sensor ICs  512 , a first sensor substrate  513   a , a second sensor substrate  513   b , signal processing ICs (ASIC)  514 , electronic components  515 , a housing  516  and a bottom plate  517 . 
     The top glass sheet  3  is a transparent glass plate that supports a document  7  such as literature, media and/or the like. The lighting unit  2  is the same as the lighting unit  2  according to the eleventh preferred embodiment, is a unit for accomplishing linear lighting on the surface of the document, and comprises LED chips  210 , an LED substrate  230 , heat-radiating plates  50  and a cylindrical parabolic mirror  20 . 
     The LED chips  210  are light sources for shining light. The LED substrate  230  is a substrate to which the LED chips  210  are anchored and which is provided with wiring for supplying electric current to the LED chips  210 . The heat-radiating plates  50  receive heat generated by the LED chips  210  via the LED substrate  230  and dissipate this heat into the air. The cylindrical parabolic mirror  20  has a mirror surface that causes light generated by the LED chips  21  in the direction of the document supported by the top glass sheet  3  to be reflected as approximately parallel light. 
     The first lens mirrors (also called the first lenses)  507  are concave first lens mirrors that receive divergent light from the document  7 . The flat mirrors  508  receive approximately parallel light from the first lenses  507  and reflect this light. The apertures  509  receive approximately parallel light from the flat mirrors  508 , block light at the periphery and restrict the light passing through. The openings  510  are provided on the surface of the apertures  509  or close thereto and are a part in which is provided an opening through which light received by the apertures  509  is allowed to pass. The second lens mirrors (also called the second lenses)  511  are concave second lens mirrors for receiving and condensing light passing through the apertures  509 . 
     The second ICs  512  (also called light receivers) receive light reflected from the second lens mirrors  511  that has passed through the openings  510 , and are sensor ICs (Integrated Circuits) having a MOS semiconductor composition comprising a photoelectric conversion circuit for accomplishing photoelectric conversion and a driver. The first sensor substrate  513   a  and the second sensor substrate  513   b  are sensor substrates on which the sensor ICs  512  are mounted, and are respectively positioned lined up in the sub-scanning direction, as shown in  FIG. 25 . The signal processing ICs (ASIC)  514  are ICs for accomplishing signal processing on signals photoelectrically converted by the sensor ICs  512 . The electronic components  515  are capacitors, resistors and/or the like mounted on the sensor substrates  513 . The housing  516  is a hollow member to which the imaging optical system that is the imaging means comprising the sensor ICs and mirrors is anchored. The bottom plate  517  is a plate-like member covering the bottom opening of the housing  516  and to which the lenses and housing  516  are anchored. 
     The action of the optical system of the image scanning device according to the twelfth preferred embodiment of the present invention will be explained. Light from the LED chips  210  is reflected by the cylindrical parabolic mirror  20  and shines on the document  7  as approximately parallel light. Scattered light reflected by the document  7  is inclined to one side in the sub-scanning direction (in the leftward direction in  FIG. 25 ) and is reflected as collimated light. Light from the first lens  507  is reflected to the flat mirror  508  inclined to one side in the sub-scanning direction. Light from the flat mirror  508  shines on the window (opening  510 ) of the aperture  509  as approximately parallel light rays. Furthermore, light radiating from the window  510  is reflected to the second lens  511  inclined to one side in the sub-scanning direction, and because this light is incident on the sensor IC  512  for each beam, the image information is imaged as an inverted image on the light-receiving surface of the sensor IC  512 . 
     Scattered light shining from the left-side lighting unit  2  and reflected by the document  7  that is the subject of illumination is inclined toward the other side (the left direction in  FIG. 25 ) in the sub-scanning direction, and is incident on the sensor IC  512  on the first sensor substrate  513   a . Scattered light shining from the right-side lighting unit  2  and reflected by the document  7  that is the subject of illumination follows a light path symmetrical to the light path shown in  FIG. 25  on a plane orthogonal to the sub-scanning direction and is incident on the sensor IC  512  on the second sensor substrate  513   b . Consequently, the light path incident on the sensor IC  512  mounted on the first sensor substrate  513   a  and the light path incident on the sensor IC  512  mounted on the second sensor substrate  513   b  do not intersect and thus it is possible to prevent light ray interference in the light path. 
     In the twelfth preferred embodiment of the present invention, the lighting unit  2  explained in the eleventh preferred embodiment of the present invention is used, but similar efficacy and results are obtained by using the lighting unit explained in the first through tenth preferred embodiments of the present invention. 
     Having described and illustrated the principles of this application by reference to one or more preferred embodiments, it should be apparent that the preferred embodiments may be modified in arrangement and detail without departing from the principles disclosed herein and that it is intended that the application be construed as including all such modifications and variations insofar as they come within the spirit and scope of the subject matter disclosed herein. 
     This application claims the benefit of priority based on Japanese Patent Application No. 2011-234079, filed on Oct. 25, 2011, the entire disclosure of which is incorporated by reference herein. 
     REFERENCE SIGNS LIST 
       1  Imaging optical system,  1   a  Imaging optical system position-determining protrusion,  2  Lighting unit,  3  Top glass sheet,  4  Substrate,  7  Document,  8  Scan line,  11  Main scanning direction,  12  Sub-scanning direction,  13  Depth direction,  20  Cylindrical parabolic mirror,  21  Semi-cylindrical parabola y+,  22  Semi-cylindrical parabola y−,  23  Cylindrical parabola focal position,  24  Cylindrical parabola vertex,  25  Cylindrical parabola axial plane,  30  Cylindrical parabolic block,  31  Cylindrical parabolic block incident surface,  32  Cylindrical parabolic block exit surface,  40  Imaging element,  50  Heat-radiating plate,  50   a  Lighting system position-determining protrusion,  51  Joining screw,  52  Structural support plate,  52   a  Imaging optical system position-determining hole,  52   b  Lighting system position-determining hole,  101  Imaging optical axis,  102  Lighting optical axis,  103  Lighting light rays,  104  Lighting region,  105  Central axis in light-emission direction,  210  LED chip,  211  LED package,  212  Blue light-emitting diode,  213  Yellow fluorescent material,  214  Blue light-emitting diode short axis,  215  Blue light-emitting diode long axis,  216  LED package top surface,  217  Yellow fluorescent material strong light-emission region,  218  LED light-emission region,  210 ,  210   a ,  210   b  LED chip,  220  LED array,  230  LED substrate,  231  Position-determining pin,  232  Reflective sheet,  300  Reflective mirror,  400  Light guide plate,  401  Light guide plate incident surface,  402  Light guide plate exit surface,  403  Light guide surface,  405  Light guide plate supporter,  410  Scatterer,  507  Concave first lens mirror (first lens),  508  Flat minor,  509  Aperture,  510  Opening,  511  Concave second lens mirror (second lens),  512  Sensor IC (light receiver),  513  Sensor substrate,  513   a  First sensor substrate,  513   b  Second sensor substrate,  514  Signal processing IC (ASIC),  515  Electronic components,  516  Housing,  517  Bottom plate