Abstract:
An exposing device is supplied capable of producing a high-resolution printing image, and being easily manufactured as the position adjustment of the lens is not necessary. In the exposing device, a radiation point array substrate that arranges plural radiation point arrays with plural radiation points in a straight line, in plural straight lines with predetermined interval; and a lens array substrate that is set up to correspond to the respective radiation point arrays and has plural lenses forming enlargement image of the radiation point array, wherein the radiation point array substrate almost parallels the lens array substrate under the condition that optical axis of each radiation point array is adjusted to that of each lens, and when a distance of the radiation points on both ends of the radiation point array is served as “SY” and an absolute value of magnification of the lens is served as “mag”, formula “SY≦12.0/mag” holds.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an exposing device in an image forming apparatus and a reading apparatus. 
       BACKGROUND OF THE INVENTION 
       [0002]    Until now, as an LED writing device (exposing device) used in an electrophotographic printer, an LED head is known to enlarge and project the light of an LED array that sets up plural LEDs in one line. 
         [0003]    In the related LED head, as the field of LEDs arranged on the LED array is smaller than the printing field of a printer, through enlarging the image of the LED array and forming it on photosensitive body drum, it is possible to form an image as large as the printing field. Further, the LEDs on the LED array are arranged in a higher density than the printing image of the printer. It may refer to Patent Document 1. 
         [0004]    As shown in FIG. 2 of Patent Document 1, the LED writing device in the patent document 1 includes a loading substrate that loads the LED array, a circular convex lens that enlarges and projects the light of the LED array and a frame fixes the loading substrate and the LED array, within the fringe of the circular convex lens is fixed tightly by the stopper and the lens fixing ring in the maintaining section of the frame. 
         [0005]    Patent Document 1: Japan patent publication of No. Heisei 07-314771. 
         [0006]    However, in the LED writing device in Patent Document 1, as only one circular convex lens enlarges and projects the light of all LEDs in a line, it is difficult to get full-resolution image. Therefore, it is impossible to get high-resolution printing image. 
         [0007]    Further, in order to get full-resolution image, the optics system becomes more complex and cost gets higher while the device also becomes larger. 
         [0008]    Moreover, as the circular convex lens is fixed by the stopper and the lens fixing ring, the position adjustment (optical axis adjustment) of the LED array and the circular convex lens is complex when the device is assembled and the productivity is low. 
       SUMMARY OF THE INVENTION 
       [0009]    It is, therefore, an objective of the invention to provide an exposing device, an image forming apparatus including the exposing device and a reading apparatus that can solve the above problem, so as to produce a high-resolution printing image, and can be easily manufactured as the position adjustment of the lens is not necessary. 
         [0010]    A first aspect of the invention is to provide an exposing device which comprises a radiation point array substrate that arranges plural radiation point arrays with plural radiation points in a straight line, in plural straight lines with predetermined interval; and a lens array substrate that is set up to correspond to the respective radiation point arrays and has plural lenses forming enlargement image of the radiation point array, wherein the radiation point array substrate almost parallels the lens array substrate under the condition that optical axis of each radiation point array is adjusted to that of each lens, and when a distance of the radiation points on both ends of the radiation point array is served as “SY” and an absolute value of magnification of the lens is served as “mag”, formula “SY≦12.0/mag” holds. 
         [0011]    A second aspect of the invention is to provide an image forming apparatus which comprises an exposing device, the exposing device includes a radiation point array substrate that arranges plural radiation point arrays with plural radiation points in a straight line, in plural straight lines with predetermined interval; and a lens array substrate that is set up to correspond to the respective radiation point arrays and has plural lenses forming enlargement image of the radiation point array, wherein the radiation point array substrate almost parallels the lens array substrate under the condition that optical axis of each radiation point array is adjusted to that of each lens, and when a distance of the radiation points on both ends of the radiation point array is served as “SY” and an absolute value of magnification of the lens is served as “mag”, formula “SY≦12.0/mag” holds. 
         [0012]    A third aspect of the invention is to provide an reading apparatus which comprises an image shooting section that arranges plural light receiving element arrays with plural light receiving elements in a straight line, in plural straight lines with predetermined interval; and a lens array substrate that is set up to correspond to each light receiving element array and has plural lens to form reduction image of manuscript image on the light receiving element array, wherein the image shooting section almost parallels the lens array substrate under the condition that optical axis of each light receiving element array is adjusted to that of each lens, and when the distance of the light receiving elements on both ends of the light receiving element array is served as “RY” and the absolute value of reduction rate of the lens is served as “red”, formula “RY≦12.0×red” holds. 
       EFFECT OF THE INVENTION 
       [0013]    According to the exposing device, the image forming apparatus and the reading apparatus of the invention, as each lens on the lens array substrate forms an enlargement image of each radiation point array on the radiation point array substrate, it is possible to get full-resolution image with simply structure and reduced numbers of parts. 
         [0014]    Further, as the optical axis of each radiation point array and each lens are formed as a unified entity, it is possible to provide easy position adjustment for the lens and have high productivity while reducing the size of the device. 
         [0015]    Further, through using the exposing device stated above, it is not necessary to adjust the position of the lens, therefore, possible to get a high precision image forming apparatus that can produce high-resolution printing image. 
         [0016]    Further, according to the invention, as each lens on the lens array substrate forms a reduction image of manuscript image on each light receiving element array in the image shooting section, it is possible to get full-resolution image with simply structure and reduced numbers of parts. 
         [0017]    Further, as the optical axis of each light receiving element array and each lens are formed as a unified entity, it is not necessary to adjust the position of the lens, therefore, possible to have high productivity while reducing the size of the device. 
         [0018]    The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a diagram showing a main structure of an image forming apparatus in embodiment 1; 
           [0020]      FIG. 2  is an exploded oblique diagram showing an LED head; 
           [0021]      FIG. 3  is a cross-sectional side view showing an LED head; 
           [0022]      FIG. 4  is a diagram showing a structure of an LED head; 
           [0023]      FIG. 5  is a diagram showing the magnification of a micro lens; 
           [0024]      FIG. 6  is a diagram showing a position of an image on the photosensitive body formed by a radiation light of LED element; 
           [0025]      FIG. 7  is a block diagram showing a structure of an LED controlling section; 
           [0026]      FIG. 8  is a diagram showing that useless radiation light of LED element is shaded in the image forming process; 
           [0027]      FIG. 9  is a diagram showing that an image is formed by a radiation light of LED element on the photosensitive body drum; 
           [0028]      FIG. 10  is a diagram showing an evaluation of image; 
           [0029]      FIG. 11  is a diagram showing an LED head in embodiment 1 and a LED head in comparison example; 
           [0030]      FIG. 12  is a diagram showing a “mag-SY” curve; 
           [0031]      FIG. 13  is a diagram showing a main structure of a reading apparatus in embodiment 2; 
           [0032]      FIG. 14  is a diagram showing a structure of a reading head; 
           [0033]      FIG. 15  is a cross-sectional side view showing a reading head; 
           [0034]      FIG. 16  is a diagram showing a structure of a light receiving element array; 
           [0035]      FIG. 17  is a diagram showing a position on a light receiving element array formed by an incident light of manuscript image; 
           [0036]      FIG. 18  is a diagram showing the reduction rate of a micro lens; 
           [0037]      FIG. 19  is a block diagram showing a structure of a reading controlling section; 
           [0038]      FIG. 20  is a diagram showing a reading head in embodiment 2 and a reading head in comparison example; and 
           [0039]      FIG. 21  is a diagram showing a “red-RY” curve. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Embodiments of the invention will be described in detail hereinbelow with reference to the drawings. Here, it is to explain an image forming apparatus in embodiment 1 of the present invention on the basis of  FIG. 1˜FIG .  12 . 
       Embodiment 1 
       [0041]      FIG. 1  is a diagram showing a main structure of an image forming apparatus in embodiment 1;  FIG. 2  is an exploded oblique diagram showing an LED head;  FIG. 3  is a cross-sectional side view showing an LED head;  FIG. 4  is a diagram showing a structure of an LED head;  FIG. 5  is a diagram showing the magnification of a micro lens;  FIG. 6  is a diagram showing a position of a image on the photosensitive body formed by a radiation light of LED element;  FIG. 7  is a block diagram showing a structure of an LED controlling section;  FIG. 8  is a diagram showing that a useless radiation light of LED element is shaded in the image forming process;  FIG. 9  is a diagram showing that an image is formed by a radiation light of LED element on the photosensitive body drum;  FIG. 10  is a diagram showing an evaluation of image;  FIG. 11  is a diagram showing an LED head in embodiment 1 and a LED head in comparison example; and  FIG. 12  is a diagram showing a “mag-SY” curve; 
         [0042]    Image forming apparatus  100  in embodiment 1 is a color electrophotographic printer  100 , wherein a toner containing pigment with resin as color material forms an image on a print medium on the basis of the image data inputted from outside. 
         [0043]    Printer  100 , as shown in  FIG. 1 , includes paper feeding cassette  60 , print medium  101  that accommodates paper feeding cassette  60 , paper feeding roller  61  that takes out print medium  101  from paper feeding cassette  60 , conveying roller  62  and  63  that convey print medium  101 , photosensitive body drum  41  as an electrostatic latent image carrying body that forms image of colors of yellow, magenta, cyan and black, developing device  5  that develops a toner image of the electrostatic latent image formed by photosensitive body drum  41  by using a toner, toner cartridge  51  that supplies the toner in developing device  5 , charging roller  42  that supplies electric charge to the surface of photosensitive body drum  41  by using fixed voltage, LED head  3  (exposing device) that radiates light selectively on the basis of the image data formed on the surface of charged photosensitive body drum  41  and forms an electrostatic latent image, cleaning blade  43  on contact to photosensitive body drum  41  that scratches the toner remained on the surface of photosensitive body drum  41 . 
         [0044]    Moreover, an image forming section includes photosensitive body drum  41  of different colors stated above, developing device  5 , toner cartridge  51 , charging roller  42 , LED head  3  and cleaning blade  43 . 
         [0045]    Further, printer  100  also has transferring roller  80  of different colors of yellow, magenta, cyan and black, transferring belt  81 , cleaning blade  43 , fixing device  9 , conveying roller  64 , ejecting roller  65  and ejecting section  7 . 
         [0046]    Transferring roller  80  is set up opposite to photosensitive body drum  41  to fix transferring belt  81  in the transferring section. It transfers the toner image formed on photosensitive body drum  41  onto print medium  101  by using fixed voltage. Transferring belt  81  then conveys print medium  101  transferred with the toner image. Cleaning blade  43  cleans the surface of transferring belt  81 . 
         [0047]    Fixing device  9  fixes the toner image formed on print medium  101  by using heat and pressure while conveying the print medium  101  fixed with the toner image to conveying roller  64 . Conveying roller  64  then conveys print medium  101  to ejecting roller  65 . Ejecting roller  65  ejects print medium  101  to ejecting section  7 . Ejecting section  7  accommodates print medium  101  that was printed. 
         [0048]    Further, rollers such as transferring belt  81 , photosensitive body drum  41 , paper feeding roller  61 , conveying roller  62  and  63 , charging roller  42  and ejecting roller  65  are rotated and driven by a motor (not shown) and a gear (not shown). Developing device  5 , LED head  3 , fixing device  9 , motors (not shown) and their electric supplies (not shown) are connected with the drive controlling device. 
         [0049]    LED head  3  stated above, as shown in  FIG. 2  and  FIG. 4 , includes LED array substrate  300  arranging LED array  30  with plural LED element  301  in a straight line in plural straight lines with predetermined interval; diaphragm board  33  with diaphragm  34  forms an aperture section stopping down the useless radiation lights of LED array  30  during the image forming process; lens array substrate  31  with plural micro lens  32  enlarges the image formed by the light of each LED array  30 . 
         [0050]    On LED array substrate  300 , diaphragm board  33  and lens array substrate  31 , LED array  30 , diaphragm  34  and micro lens  32  are set up opposite to each other and formed as a unified entity. 
         [0051]    LED array  30  stated above, as shown in  FIG. 3 , is set up in a line with predetermined interval “P” in the same arrangement direction as LED element  301 . Micro lens  32  and diaphragm  34  are set up in straight lines with predetermined interval as LED array  30  and parallel the arrangement direction of LED array  30 . The center of the arrangement direction of LED element on LED array  30 , diaphragm  34  and micro lens  32  are set up under the conditions that the optical axis of them are in unison. 
         [0052]    Here, the interval between LED array  30  and micro lens  32  is served as “LO”; the interval between the incidence surface and the radiation surface of micro lens  32  is served as “TH”. The interval of micro lens  32  and photosensitive body drum  41  served as is “LI”; the interval of LED array  30  and photosensitive body drum  41  is served as “LT”. The radius of micro lens  32  is served as “RL”; the absolute value of the magnification is served as “mag”. The aperture radius of diaphragm  34  is served as “RA”. 
         [0053]    LED array  30 , as shown in  FIG. 4 , is formed by arranging plural LED element  301  serving as the radiation point in a straight line with predetermined interval “EP”. LED elements  301  forms a square with side length “EY”. Further, in the field of LED element  301  arranged on LED array  30 , the length of the arrangement direction of LED element  301  is “SY”. That is, the distance between LED element  301  on both ends of LED array  30  is “SY”. 
         [0054]    Moreover, the resolution of LED array  30  “SR” is shown by the number of LED element  301  arranged in every 1 inch (25.4 mm). Its unit is “dpi” (dot per inch). 
         [0055]    Each micro lens  32  on lens array substrate  31  stated above is composed of one piece of lens. 
         [0056]    Each surface of micro lens  32  in embodiment 1 is non-spherical shape, which can be shown by arithmetic formula 1 as follows. 
       &lt;Arithmetic Formula 1&gt; 
       [0057]    
       
         
           
             
               
                 
                   
                     Z 
                      
                     
                       ( 
                       r 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         r 
                         CY 
                       
                       
                         1 
                         + 
                         
                           
                             1 
                             - 
                             
                               
                                 r 
                                 2 
                               
                               
                                 CY 
                                 2 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       ARr 
                       4 
                     
                     + 
                     
                       
                         BRr 
                         6 
                       
                        
                       
                           
                       
                        
                       … 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Arithmetic 
                      
                     
                         
                     
                      
                     formula 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0058]    In arithmetic formula 1, “r”(mm) is the coordinate of the radius direction serving as the center of the optical axis of the lens surface; “CY” (mm) is curvature radius; AR and BR are non-spherical surface coefficient. 
         [0059]    Lens array substrate  31  with plural micro lens  32  that were formed as a unified entity uses optics resin such as cycloolefin resin (ZEONEX (zeonex) E48R, manufactured by Japanese Zeon Cooperation) to form a shooting formation shape. 
         [0060]    Here, it is to explain the magnification of micro lens  32  stated above on the basis of  FIG. 5 . 
         [0061]    As shown in  FIG. 5 , a surface that was separated from “LO” by the incidence surface of micro lens  32  in the direction of the optical axis of micro lens  32  is served as surface “SO”; a surface that was separated from “LI” by the radiation surface of micro lens  32  in the direction of the optical axis of micro lens  32  is served as surface “SI”. Further, the crosspoint of surface “SO” and the optical axis of micro lens  32  is served as origin “O”; and the position of the light source is served as “OY”. When micro lens  32  forms an inverted image and the position of the formation image formed on surface “SI” by the light source is served as “IY”, the magnification of micro lens  32  becomes “−IY/OY”. Therefore, the absolute value of the magnification of micro lens  32  “mag” becomes “IY/OY”. 
         [0062]    In embodiment 1, when the absolute value of the magnification of micro lens  32  is served as “mag”; the arrangement interval of LED element  301  is served as “EP”; the length of the arrangement direction of the LED array  30  is served as “SY”; and the arrangement interval of the LED array  30  is served as “P”, a LED head that satisfies the formula “P=mag×(SY+EP)” is formed. 
         [0063]    Next, it is to explain the relation of the position of the formation image formed by the radiation light of each LED element  301  on LED array  30  on the basis of  FIG. 6 . 
         [0064]      FIG. 6  is an example showing the arrangement of 188 LED element  301  on LED array  30 . At this time, the resolution of LED array  30  “SR” is 1200 dpi and the length of the arrangement direction of LED element  301  “SY” is 4.0 mm. 
         [0065]    In  FIG. 6 , there are 188 dot images formed on photosensitive body drum  41  by the radiation light of LED element  301  in each line. The three lines are set as “A”, “B” and “C”, and the dots are set as “A- 1 ”, “A- 2 ”, . . . “A- 187 ”, “A- 188 ”, “B- 1 ”, “B- 2 ”, . . . “B- 187 ”, “B- 188 ”, “C- 1 ”, “C- 2 ”, . . . “C- 187 ”, “C- 188 ” from the top to the bottom. At this time, as each micro lens  32  forms an inverted enlargement image, LED element  301  corresponding to each dot image is set as “A- 1 ”, “A- 2 ”, . . . “A- 187 ”, “A- 188 ”, “B- 1 ”, “B- 2 ”, . . . “B- 187 ”, “B- 188 ”, “C- 1 ”, “C- 2 ”, . . . “C- 187 ”, “C- 188 ” from the top to the bottom. 
         [0066]    Hence, in LED head  3  in embodiment 1, as the dot image is enlarged and formed by LED element  301  on each LED array  30  with predetermined interval, images are formed in a continuous line on photosensitive body drum  41 . 
         [0067]    Further, printer  100  includes an outer device that receives the image data and LED controlling section  200  that controls LED head  3  on the basis of the receiving data. 
         [0068]    LED controlling section  200  stated above, as shown in  FIG. 7 , includes inputting and outputting device  201  that receives the image data from the outer device such as the outer terminal and network, storing device  203  that temporarily stores the receiving image data, image processing device  202  that reads the image data in storing device  203  and changes it into a page data of colors of cyan, magenta, yellow, black that can be printed on print medium  101 . Further, in LED array substrate  300 , shift register  211 , latch circuit  212  and drive circuit  213  are installed to output one-line page data from image processing device  202  stated above to LED head  3  according to each color. 
         [0069]    Next, it is to explain the action of printer  100  in embodiment 1 on the basis of  FIG. 1 . 
         [0070]    The surface of photosensitive body drum  41  is charged by charging roller  42  that was driven by a power supply device (not shown). After photosensitive body drum  41  rotates, the charged surface of photosensitive body drum  41  gets around LED head  3 ; the surface of photosensitive body drum  41  is exposed by LED head  3 ; and the electrostatic latent image is formed on the surface of photosensitive body drum  41 . 
         [0071]    The electrostatic latent image on photosensitive body drum  41  is developed by developing device  5 ; and the toner image is formed. 
         [0072]    On the other hand, print medium  101  set up in paper feeding cassette  60  was taken out from paper feeding cassette  60  by paper feeding roller  61 , then is conveyed around transferring roller  80  and transferring belt  81  by conveying roller  62  and  63 . 
         [0073]    Further, after print medium  101  gets around transferring roller  80  and transferring belt  81 , the toner image on photosensitive body drum  41  is transferred by transferring roller  80  and transferring belt  81  that were charged by a power supply device (not shown). Then, print medium  101  transferred with the toner image is conveyed to fixing device  9  by transferring belt  81 . 
         [0074]    The toner image on print medium  101  is melted by the pressure and heat of fixing device  9  and fixed on print medium  101 . Furthermore, the fixed print medium  101  is ejected to ejecting section  7  by conveying roller  64  and ejecting roller  65 . 
         [0075]    Next, it is to explain the action of LED head  3  stated above on the basis of  FIG. 7  and  FIG. 8 . In LED controlling section  200 , the image data was inputted by an outer device (outer terminal, network) through inputting and outputting device  201  and temporarily stored in storing device  203 . Then it is changed into the page data serving as the controlling data of LED head  3  in image processing device  202 . The image data of black is changed into the page data of black; while the color images data is changed into the page data of colors of cyan, magenta, yellow, black. The page data of each color changed by image processing device  202  is sent to LED head  3  of different colors. The page data (for example, black) from image processing device  202  is conveyed and stored into shift register  211  orderly one line by one line as serial image data. And every one-line image data is stored in latch circuit  212  orderly. Then, drive circuit  213  drives (radiates) the LED element selectively on the basis of the storing data in latch circuit  212 . Similarly, the page data of colors of yellow, magenta and cyan is sent to different LED head  3  and drives LED element  301  on LED array  30 . 
         [0076]    The radiation light controlled by drive circuit  213  is inverted, enlarged and projected onto the surface of photosensitive body drum  41  by the micro lens  32 . And dots form images with predetermined interval “IP” in parallel with the arrangement direction of LED element  301 . Moreover, in the radiation light of LED element  301 , the useless light (stray light), as shown in  FIG. 8 , is shaded by diaphragm  34  on diaphragm board  33  during the image forming process. 
         [0077]    The arrangement interval of the dot “IP” is shown by formula “IP=mag×EP”. Here, “EP” refers to the arrangement interval of LED element  301  and “mag” refers to the absolute value of magnification of micro lens  32 . 
         [0078]    Further, the resolution of LED head  3  “IR” is shown by the number of the dot formed on the photosensitive body drum  41  in 1 inch. The resolution of LED head  3  “IR” is shown by formula “IR=SR/mag”. Here, “SR” refers to the resolution (dpi) of LED array  30  “SR” and “mag” refers to the absolute value of magnification of micro lens  32 . 
         [0079]    Here, it is to explain the image forming process in which the radiation light from each LED array  30  in LED head  3  forms image on photosensitive body drum  41  on the basis of  FIG. 9 . 
         [0080]    Moreover, it is to explain an example in which 188 LED elements  301  are arranged on each LED array  30 ; the absolute value of magnification of each micro lens  32  “mag” is doubled; and the arrangement pitch of micro lens  32  “P” is 8 mm. 
         [0081]    At this time, the resolution of LED array  30  “SR” is 1200 dpi, the length of the arrangement direction of LED element  301  “SY” is 4.0 mm. Further, the resolution of the dot formed on photosensitive body drum  41  “IR” is 600 dpi; and the arrangement pitch of the dot “IP” is 0.0424 mm. 
         [0082]    As shown in  FIG. 9 , after LED element  301  “EA 94 ” on the optical axis of micro lens  32  on the upper part of the figure radiates, a dot with formation image “IA 94 ” is formed on the optical axis of the micro lens  32  on the upper part of the figure. After LED element  301  “EA 188 ” radiates, a dot with formation image “IA 188 ” is formed 0.0424 mm above dot “IBI” that contains image formed by LED element  301  “EBI”. After LED element  301  “EB 94 ” on the optical axis of micro lens  32  on the center of the figure radiates, a dot with formation image “IB 94 ” is formed on the optical axis of micro lens  32  on the center of the figure. After LED element  301  “EB 188 ” radiates, a dot with formation image “IB 188 ” is formed 0.0424 mm above dot “ICI” that contains image formed by LED element  301  “EC 1 ”. After LED element  301  “EC 94 ” on the optical axis of micro lens  32  on the lower part of the figure radiates, a dot with formation image “IC 94 ” is formed on the optical axis of the micro lens  32  on the lower part of the figure. 
         [0083]    Next, in order to confirm the effect of embodiment 1 of the present invention, different printing images were evaluated by using printer  100  that installs LED head  3  (exposing device) in embodiment 1˜6 and comparison example 1˜6 in  FIG. 11 . 
         [0084]    Moreover, in  FIG. 11 , aperture number N.A. (Numerical Aperture) can be shown as sin(θ) when θ° is served as the half angle of the maximum vertical angle of the circular cone of the incidence light from the lens. Because the maximum volume of the aperture number is 1, the larger the aperture number is, the more light the lens can take in. Therefore, it is possible to obtain bright image. 
         [0085]    Further, MTF (Modulation Transfer Function) shows the resolution of the exposing device and the contrast of the light quantity of the image formed by the radiation LED element in the exposing device. The maximum contrast of the formation image is 100%. At this time, the resolution of the exposing device is high. The smaller MTF is, the smaller the contrast of the light quantity is and the lower the resolution of the exposing device becomes. 
         [0086]    When the maximum volume of the light quantity of the formation image is served as “Imax” and the minimum volume of the light quantity of the two adjacent formation images is served as “Imin”, the MTF(%) can be shown by arithmetic formula 2 as follows. 
         [0000]      &lt;MTF&gt;( I max− I min)/( I max+ I min)×100%   arithmetic formula 2 
         [0087]    The evaluation of the image, as shown in  FIG. 10 , performs the printing process by using the evaluation image data formed by 1 tonder dot with interval of 0.0846 mm, that is, in the whole dot that can be formed in 600 dpi, performs the printing process by using the evaluation image data that formed by a dot. Then it evaluates the uniformity of the image concentration of the printing image in embodiment 1˜6 and comparison example 1˜6 one by one. 
         [0088]    The result shows that when LED head  3  in embodiment 1˜6 is used, it is possible to get a good image with uniform concentration. On the other hand, when LED head  3  in comparison example 1˜6 is used, a white line by can be seen in one part of the evaluation image because the high concentration line in the cross direction of the arrangement direction of LED element  301  and the tonner image are not formed here. 
         [0089]    Further, the formation image of the evaluation image stated above is shot by a microscope digital camera. The image is located at position “LI(mm)” from the side surface of the formation image surface side (photosensitive body drum  41  side) of lens array substrate  31  on lens array substrate  31 . And MTF is calculated by analyzing the distribution of the light quantity of the image formed by LED element  301  through the shooting image. 
         [0090]    The result shows that in the image evaluation stated above, when the images are good in embodiment 1˜6, MTF is over 85%. On the other hand, when a line can be seen in one part of the evaluation image in comparison example 1˜6, MTF is under 75%. 
         [0091]    Here,  FIG. 12  shows the relation between the absolute value of the magnification of micro lens  32  “mag” and the length of LED array  30  “SY” when the images are good in LED head  3  in embodiment 1˜6. The black circles in the figure that meet the requirement in embodiment 1˜6 are on curve “SY=12.0/mag”. Further, because the shorter the length “SY” is, the better the optical resolution is, it is possible to form printer  100  that can printing high-resolution image if LED head  3  satisfies arithmetic formula 2 as follows. 
         [0000]        SY≦ 12.0/mag   arithmetic formula 3 
         [0092]    Therefore, as shown in  FIG. 10 , the formula becomes “SY&gt;12.0/mag” in comparison example 1˜6. 
         [0093]    Further, plural LED heads with different length of LED array  30  “SY” (not shown), but same aperture number “N.A” and the absolute value of the magnification “mag” are manufactured and their MTF is compared. As shown in the result, the shorter the length of LED array  30  “SY” is, the higher the MTF of the formation image of LED element  301  is. That is, when the aperture number “N.A.” and the absolute value of the magnification “mag” are the same, the shorter the length of LED array  30  “SY” is, the better the optical resolution is. 
         [0094]    According to embodiment 1 of the present invention, as each micro lens  32  on lens array substrate  31  forms an enlargement image of each LED array  30  on LED array substrate  300 , it is possible to get full-resolution image with simply structure and reduced numbers of parts. 
         [0095]    Further, as the optical axis of each LED array  30  and each micro lens  32  are formed as a unified entity, it is not necessary to adjust the position of the lens, therefore, possible to provide easy position adjustment for the lens and have high productivity while reducing the size of the device. 
         [0096]    Further, when the distance of the radiation point on the both ends of LED array  30  is served as “SY” and the absolute value of magnification of micro lens  32  is served as “mag”, it is possible to form a high-resolution exposing device that can improve the resolution of the formation image if formula “SY≦12.0/mag” holds. 
         [0097]    At this time, it is more desirable if the distance of the radiation point “SY” becomes 2.0˜6.0 mm and the absolute value of magnification of micro lens  32  “mag” becomes 2.0˜4.0. 
         [0098]    If “SY” is under 2.0 mm, in order to confirm a fixed exposure field, the number of parts is increased because of the increasing number of necessary LED array  30  and micro lens  32 ; and if “SY” is over 4.0 mm, the exposing device becomes large because of the longer distance from LED array  30  to the surface of the formation image. 
         [0099]    Further, if “mag” is under 2, in order to get a fixed enlargement image, it is necessary to enlarge the size of LED element  301  and this will raise the manufacture cost; and if “mag” is over 4, during image forming process, the disorder of the position of LED element  301  arranged in a straight line is intensified and the quality of the print is deteriorated. 
         [0100]    Further, diaphragm  34  that stops down the radiation light from each LED array  30  is set up between LED array substrate  300  and lens array substrate  31  so as to shade the useless light in the image forming process. It is also possible to prevent the influence of the light from adjacent LED array  30 . Therefore, the resolution of the formation image is further improved. 
         [0101]    Further, because plural micro lens  32  were formed as a unified entity, it is possible to improve the degree of precision of the position of individual micro lens  32  and the degree of precision of the center position of each lens surface. Therefore, it is possible to reduce the assembling error during the manufacture process as well as reduce the number of parts and improve the productivity. 
         [0102]    Above is the explanation of a color electrophotographic printer serving as an image forming apparatus in embodiment 1. However, the present invention is not limited to the foregoing embodiments but many modifications and variations are possible within the spirit and scope of the appended claims of the invention. It can also be applied to electrophotographic facsimile, copying machine, or multi-functional machine with plural functions. It may also form monochrome image besides color image. 
         [0103]    Further, LED array  30  is composed of a single tip, but it also may be composed of plural adjacent tips. 
         [0104]    Further, lens array substrate  31  uses plural micro lens  32  which were formed as a unified entity, but it may also use individual micro lens  32 . 
         [0105]    Further, micro lens  32  is composed of a single piece of lens, but it also may be composed of plural lens in the direction of the optical axis. 
         [0106]    Further, the surface of micro lens  32  is not limited to non-spherical surface shape, the surface shape of one direction can be different from the surface shape of other directions. It may be non-axis contrastive anamorphic non-spherical surface, troy dull surface and cylinder surface corresponding to the optical axis, as well as well-known free curved surface. Hence, the aberration of the lens is reduced and the resolution can be improved. Further, micro lens  32  may also be served as spherical surface and paraboloid. Hence, the optics characteristic declines when the comparative aberration is big. But it can be manufactured comparatively easily and its degree of precision is good, thus the productivity can be improved. 
       Embodiment 2 
       [0107]    Next, it is to explain a reading apparatus in embodiment 2 in the present invention on the basis of  FIG. 13˜FIG .  21 . 
         [0108]      FIG. 13  is a diagram showing a main structure of a reading apparatus in embodiment 2;  FIG. 14  is a diagram showing a structure of a reading head;  FIG. 15  is a cross-sectional side view showing a reading head;  FIG. 16  is a diagram showing a structure of a light receiving element array;  FIG. 17  is a diagram showing a position on a light receiving element array formed by an incident light of manuscript image;  FIG. 18  is a diagram showing the reduction rate of a micro lens;  FIG. 19  is a block diagram showing a structure of a reading controlling section;  FIG. 20  is a diagram showing a reading head in embodiment 2 and a reading head in comparison example; and  FIG. 21  is a diagram showing a “red-RY” curve. 
         [0109]    Scanner  500  serving as a reading apparatus in embodiment 2, as shown in  FIG. 13 , includes manuscript stand  502  on which manuscript  507  is set up, reading head  400  that reads out the manuscript, rail  503  that upholds reading head  400 , drive belt  505  that moves reading head  400 , pulley  504  that extends drive belt  505 , motor  506  that rotates pulley  504  and drives drive belt  505 . Drive belt  505  is connected with reading head  400 . 
         [0110]    Reading head  400  stated above changes the image of the light that reflects on the surface of manuscript  507  into a taking-in electricity signal. It includes lamp  501  that radiates the light onto manuscript  507  as shown in  FIG. 14 , mirror  402  that changes the route of the light reflected from manuscript  507 , lens array substrate  431  that incidents the reflection light of mirror  402  and forms the formation image of the manuscript image, line sensor  410  serving as a shooting section that changes the formation image of the manuscript image into a electricity signal, diaphragm board  433  with plural forms diaphragm  434  that forms an aperture section shading the useless light in the image forming process of the manuscript image. 
         [0111]    Lens array substrate  431  stated above is composed of one piece of lens arranging plural micro lens  432  in a straight line. Micro lens  432  on lens array substrate  431  and diaphragm  434  on diaphragm board  433  are set up opposite to each other and formed as a unified entity. Moreover, lens array substrate  431  is formed by the same material as lens array substrate  31  in embodiment 1 stated above. 
         [0112]    Further, line sensor  410  is formed by arranging light receiving element array  401  (according to  FIG. 16 ) with plural light receiving element  403  in a straight line in plural straight lines with predetermined interval. 
         [0113]    Light receiving element array  401  stated above, as shown in  FIG. 15 , is set up in a line with predetermined interval “P” in the same direction as the arrangement direction of light receiving element  403 . Micro lens  432  and the diaphragm  434  are set up in a straight line with fix interval as light receiving element array  401  and parallel the arrangement direction of the light receiving element  403 . The center of the arrangement direction of the light receiving element on light receiving element array  401 , diaphragm  434  and micro lens  432  are formed as unified entity under the conditions that the optical axis of them are in unison. 
         [0114]    Here, the interval between manuscript  507  and micro lens  432  is served as “LI”; the interval between incidence surface and radiation surface of micro lens  432  is served as “TH”. The interval of micro lens  432  and light receiving element array  401  is served as “LO”; the interval of light receiving element array  401  and manuscript  507  is served as “LT”. The radius of micro lens  432  is served as “RL”; the absolute value of the reduction rate is served as “red”. The aperture radius of diaphragm  434  is served as “RA”. 
         [0115]    Light receiving element array  401  stated above, as shown in  FIG. 16 , is formed by arranging plural light receiving element  403  in a straight line with predetermined interval “RP”. Light receiving element  403  forms a square. Further, in the field of light receiving element  403  arranged on light receiving element array  401 , the length of the arrangement direction of light receiving element  403  is “RY”. That is, the distance between light receiving elements  403  on both ends of light receiving element  403  is “RY”. 
         [0116]    Moreover, the resolution of light receiving element array  401  “SR” is shown by the number of light receiving element  403  arranged in every 1 inch. Its unit is “dpi”. 
         [0117]    Here, it is to explain the reduction rate of micro lens  432  stated above on the basis of  FIG. 18 . 
         [0118]    As shown in  FIG. 18 , in the direction of the optical axis of micro lens  432 , a surface that was separated from “LO” by the radiation surface of micro lens  432  is served as surface “SI”; a surface that was separated from “LI” by the incidence surface of micro lens  432  in the direction of the optical axis of micro lens  432  is served as surface “SO”. Further, the crosspoint of surface “SO” and the optical axis of micro lens  432  is served as origin “O”; and the position of the light source is served as “OY”. When micro lens  432  forms an inverted image and the position of the formation image formed on surface “SI” by the light source is served as “IY”, the reduction rate of micro lens  432  becomes “−IY/OY”. Therefore, the absolute value of the reduction rate of micro lens  432  “red” becomes “IY/OY”. 
         [0119]    Moreover, the structure and the interval of lens array substrate  431 , diaphragm board  433  and diaphragm  434  in embodiment 2 are the same as the ones in LED head  3  in embodiment 1 stated above. 
         [0120]    In embodiment 2, when the absolute value of the reduction rate of micro lens  432  is served as “red”; the arrangement interval of light receiving element  403  is served as “RP”; the length of the arrangement direction of light receiving element array  401  is served as “RY”; and the arrangement interval of light receiving element array  401  is served as “P”, a line sensor  410  that satisfies of the formula “P=(RY+RP)/red” is formed. 
         [0121]    Next, it is to explain the relation of the position of light receiving element  403  arranged on light receiving element array  401  according to the manuscript image on the basis of  FIG. 17 . 
         [0122]      FIG. 17  is an example showing the arrangement of 188 light receiving elements  403  on light receiving element array  401 . At this time, the resolution of light receiving element  403  “RP” is 1200 dpi and the length of the arrangement direction of light receiving element  403  “RY” is 4.0 mm. 
         [0123]    In  FIG. 17 , there are 188 dots of the manuscript image in each line. The three lines are set as “A”, “B” and “C”, and the dots are set as “A- 1 ”, “A- 2 ”, . . . “A- 187 ”, “A- 188 ”, “B- 1 ”, “B- 2 ”, . . . “B- 187 ”, “B- 188 ”, “C- 1 ”, “C- 2 ”, . . . “C- 187 ”, “C- 188 ” from the top to the bottom. At this time, as each micro lens  432  on lens array substrate  431  forms a inverted reduction image, light receiving element  403  corresponding to each dot of the manuscript image is set as “A- 1 ”, “A- 2 ”, . . . “A- 187 ”, “A- 188 ”, “B- 1 ”, “B- 2 ”, . . . “B- 187 ”, “B- 188 ”, “C- 1 ”, “C- 2 ”, . . . “C- 187 ”, “C- 188 ” from the top to the bottom. 
         [0124]    Further, scanner  500  includes reading controlling section  520  that controls the sending of the image digital data on the basis of the requirement read from the outer device (outer terminal and network). 
         [0125]    Reading controlling section  520 , as shown in  FIG. 19 , includes inputting and outputting power device  514 , controlling device  513 , storing device  512 , A/D changing section  510  and image processing device  511 . 
         [0126]    Next, it is to explain the action of scanner  500  in embodiment 2 on the basis of  FIG. 13 ,  FIG. 14  and  FIG. 19 . 
         [0127]    As shown in  FIG. 19 , after inputting and outputting power device  514  received a requirement of the image digital data read from the outer device; as shown in  FIG. 13 , lamp  501  of scanner  500  is on; the surface of manuscript  507  installed on manuscript stand  502  is lightened; and the reflection light on the surface of manuscript  507  is taken into reading head  400 . The rotation of motor  506  drives drive belt  505 ; reading head  400  and lamp  501  move in horizontal horizontality as a unified entity; and reading head  400  in the middle of them takes in the reflection light from the whole manuscript. 
         [0128]    That is, in  FIG. 14 , the reflection light from manuscript  507 , penetrates manuscript stand  502  and incidents in each micro lens  432  on lens array substrate  431  whose light route is changed by mirror  402 . At this time, in the incidence light on lens array substrate  431 , the useless light (stray light) is shaded by diaphragm board  433  in the image forming process of the manuscript image. The formation image of the manuscript image that was inverted and reduced in the absolute value of the reduction rate “red” by each micro lens  432  is formed on each light receiving element array  401  of line sensor  410 . On light receiving element array  401 , the luminance information of the formation image is changed into the analog signal. 
         [0129]    The analog signal outputted from light receiving element array  401 , as shown in  FIG. 19 , is inputted into A/D changing section  510  and changed into the digital data. Furthermore, after a fixed revision process is done in image processing device  511 , the digital data of the manuscript image is temporarily stored into storing device  512  through controlling device  513 . Then, the digital data of the manuscript image stored in storing device  512  is sent to the outer device through controlling device  513  and inputting and outputting power device  514  according to the requirement read from the outer device. 
         [0130]    Next, in order to confirm the effect of embodiment 2 of the present invention, the manuscript image was evaluated by using scanner  500  that installs reading head  400  in embodiment 1˜6 and comparison example 1˜6 in  FIG. 20 . 
         [0131]    The evaluation of the image, as shown in  FIG. 10 , performs the printing process by using the evaluation image data formed by 1 dot with interval of 0.0846 mm, that is, in the whole dot that can form in 600 dpi, performs the printing process by using the evaluation image data that formed a dot. Then it fomrs the digital data (image data) of the evaluation image in reading head  400  in embodiment 1˜6 and comparison example 1˜6 and evaluates the image reading condition (shade quality of the image data) on the basis of the image data. 
         [0132]    The result shows that when reading head  400  in embodiment 1˜6 is used, it is possible to avoid bad reading problem and get a good image with uniform concentration. On the other hand, when reading head  400  in comparison example 1˜6 is used, bad reading problem occurs because a liner concentration difference happens in the cross direction of the arrangement direction of light receiving element  403 . 
         [0133]    Further, because lens array substrate  431  of reading head  400  in embodiment 1˜6 and comparison example 1˜6 has the same structure as lens array substrate  31  of LED head  3  in embodiment 1 stated above, MTF that shows the resolution of the formation image is shown in  FIG. 11 . 
         [0134]    That is, when the images are good in embodiment 1˜6, MTF is over 85%. On the other hand, when bad reading problems occur in comparison example 1˜6, MTF is under 75% 
         [0135]    Here,  FIG. 21  shows the relation between the absolute value of the reduction rate of micro lens  432  “red” and the length of light receiving element array  401  “RY” when the image data is good in reading head  400  in the embodiment 1˜6 The black squares that meet the requirement in embodiment 1˜6 are on straight line “RY=12.0×red”. 
         [0136]    Further, when the aperture number “N.A.” and the absolute value of the reduction rate of micro lens  432  “red” are the same, the shorter the length of the light receiving element array “RY” is, the better the resolution of micro lens  432  is. Therefore, it is possible to form scanner  500  that does not have bad reading problem if reading head  400  satisfies arithmetic formula 4 as follows. 
         [0000]        RY≦ 12.0×red   arithmetic formula 4 
         [0137]    Therefore, as shown in  FIG. 20 , the formula becomes “RY&gt;12.0×red” in comparison example 1˜6. Further, when the reduction rate is the same, the size of light receiving element  403  in embodiment 1˜6 is smaller than the one in comparison example 1˜6. 
         [0138]    According to embodiment 1 of the present invention, as each 1 micro lens  432  on lens array substrate  431  forms a reduction image of the manuscript image on each light receiving element array  401  arranged on line sensor  410 , it is possible to get full-resolution image with simply structure and reduced numbers of parts. 
         [0139]    Further, as the optical axis of each light receiving element array  401  and each micro lens  432  are formed as a unified entity, it is not necessary to adjust the position of the lens, therefore, possible to provide easy position adjustment for the lens and have high productivity while reducing the size of the device. 
         [0140]    Further, when the distance of the light receiving element on both ends of light receiving element array  401  is served as “RY” and the absolute value of the reduction rate of micro lens  432  is served as “red”, it is possible to form high-resolution reading apparatus  500  that can improve the resolution of the formation image if formula “SY≦12.0×red” holds. 
         [0141]    Further, diaphragm board  43  that stops down the radiation light from each lens is set up between line sensor  410  and lens array substrate  431  so as to shade the useless light in the image forming process. It is also possible to prevent the influence of the radiation light from the adjacent lens. Therefore, the resolution of the formation image is further improved. 
         [0142]    Further, because plural micro lens  432  were formed as a unified entity, it is possible to improve the degree of precision of the position of individual lens and the degree of precision of the center position of each lens surface. Therefore, it is possible to reduce the assembling error during the manufacture process as well as reduce the number of parts and improve the productivity. 
         [0143]    Above is the explanation of a scanner serving as a reading apparatus that changes the manuscript image into the digital data in embodiment 2. However, the present invention is not limited to the foregoing embodiments but many modifications and variations are possible within the spirit and scope of the appended claims of the invention. It can also be applied to sensor and switch that changes optics signal into electrical signal, as well as inputting and outputting power device, biometric authentication device, communication device and scanning micrometer that use the sensor and switch stated above. 
         [0144]    Further, the line sensor serving as shooting section  410  can also be applied to area sensor. 
         [0145]    The present invention is not limited to the foregoing embodiments but many modifications and variations are possible within the spirit and scope of the appended claims of the invention.