Abstract:
A light irradiation element includes a cavity through which light passes and a translucent light conduit bordering the cavity, allowing light to pass therethrough and transmitting the light passed through the cavity, the light irradiation element being disposed along a longitudinal direction of an image bearing body on which an electrostatic latent image is formed and directing the light passed through the light conduit to irradiate the image bearing body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/135,689, filed on Jun. 9, 2008, which is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-266436 filed Oct. 12, 2007, Japanese Patent Application No. 2007-327539 filed Dec. 19, 2007, and Japanese Patent Application No. 2008-075075 filed Mar. 24, 2008. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a light irradiation element, an image forming structure, and an image forming apparatus. 
         [0004]    2. Related Art 
         [0005]    In an image forming apparatus of this type, an image bearing body is charged by a charging device, a latent image is formed by an optical projection device and is made visible by a development device, and a developer image thus formed on the image bearing body is transferred onto a paper sheet. After the transfer, electric charges on the image bearing body are removed by an optical charge-erasing device. 
       SUMMARY 
       [0006]    According to an aspect of the invention, the invention resides in a light irradiation element including a cavity through which light passes and a translucent light conduit bordering the cavity, allowing light to pass therethrough and transmitting the light passed through the cavity, the light irradiation element being disposed along a longitudinal direction of an image bearing body on which an electrostatic latent image is formed and directing the light passed through the light conduit to irradiate the image bearing body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0008]      FIG. 1  depicts an image forming apparatus  10  in accordance with an exemplary embodiment of the invention; 
           [0009]      FIG. 2  depicts an image forming subunit  64 , focusing on an image bearing body  40  and an optical charge-erasing device  46 ; 
           [0010]      FIG. 3  depicts the optical charge-erasing device  46 , focusing on the side cross section of a light irradiation element  68 ; 
           [0011]      FIG. 4  shows the cross section of the light irradiation element  68  when viewed from a light emission member  70 ; 
           [0012]      FIG. 5  depicts a reflection part  72  when viewed from the open side facing the image bearing body  40 ; 
           [0013]      FIGS. 6A and 6B  are graphs that represent a relationship between the amount of light irradiating the image bearing body  40  and the distance from the light emission member  70 ; 
           [0014]      FIGS. 7A through 7G  show cross sectional views of light irradiation elements  68  according to second through eighth exemplary embodiments; 
           [0015]      FIG. 8  shows a side cross section of the light irradiation element  68  according to a ninth exemplary embodiment; 
           [0016]      FIG. 9  shows a side cross section of the light irradiation element  68  according to a tenth exemplary embodiment; 
           [0017]      FIG. 10  shows a cross section of a light conduit  76  in the light irradiation element  68  according to an eleventh exemplary embodiment; 
           [0018]      FIG. 11  depicts an optical charge-erasing device  46 , focusing on the side cross section of the light irradiation element  68  according to a twelfth exemplary embodiment; 
           [0019]      FIG. 12  depicts an optical charge-erasing device  46 , focusing on the side cross section of the light irradiation element  68  according to a thirteenth exemplary embodiment; 
           [0020]      FIG. 13  is an enlarged view of a section surrounded by dotted lines in  FIG. 12 ; 
           [0021]      FIGS. 14A and 14B  are graphs that represents a relationship between the amount of light irradiating the image bearing body  40  and the distance from the light emission member  70 ; 
           [0022]      FIG. 15  shows a side cross section of the light irradiation element  68  according to a fourteenth exemplary embodiment; 
           [0023]      FIG. 16  shows a side cross section of the light irradiation element  68  according to a fifteenth exemplary embodiment; 
           [0024]      FIG. 17  is an enlarged view of a part of a side cross section of the light irradiation element  68  according to a sixteenth exemplary embodiment; 
           [0025]      FIG. 18  is an enlarged view of a part of a side cross section of the light irradiation element  68  according to a seventeenth exemplary embodiment; 
           [0026]      FIG. 19  depicts an optical charge-erasing device  46 , focusing on the side cross section of the light irradiation element  68  according to an eighteenth exemplary embodiment; 
           [0027]      FIG. 20  shows an A-A cross section of the light irradiation element  68  according to the eighteenth exemplary embodiment used in the image forming apparatus; 
           [0028]      FIG. 21  depicts an optical charge-erasing device  46 , focusing on the side cross section of the light irradiation element  68  according to an nineteenth exemplary embodiment; 
           [0029]      FIG. 22  shows a cross section of a light irradiation element formed in an alternative shape; and 
           [0030]      FIG. 23  shows a cross section of a light irradiation element formed in an alternative shape. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    To begin with, a first exemplary embodiment of the invention is described. 
         [0032]      FIG. 1  depicts an image forming apparatus  10  in accordance with an exemplary embodiment of the invention. 
         [0033]    As shown in  FIG. 1 , the image forming apparatus  10  has an image forming apparatus main body  12 . A paper feeder  14  is placed at the bottom of the image forming apparatus main body  12  and a paper collector  16  is formed at the top of the image forming apparatus main body  12 . 
         [0034]    The paper feeder  14  has a paper tray  18  and a lot of paper sheets are stacked in the paper tray  18 . On the upper corner of one end of the paper tray  18 , a feed roller  20  is placed and a retard roller  22  is positioned in abutting contact with the feed roller  20 . From the paper stack in the paper tray  18 , a top sheet is picked up by the feed roller  20  and separated from another and transported by cooperation of the feed roller  20  and the retard roller  22 . 
         [0035]    A paper sheet being transported from the paper tray  18  is once stopped by registration rollers  24  and, at a predetermined timing, further transported between an image bearing unit  26  which will be described later and a transfer unit  28 . After passing through a fixing device  30 , the sheet is ejected by eject rollers  32  to the paper collector  16 . 
         [0036]    In the image forming apparatus main body  12 , the image bearing unit  26  installed removably from the image forming apparatus main body  12 , the transfer unit  28 , a power supply unit  34 , toner boxes  50 , optical projection devices  56 , and a controller  36  are arranged. The controller  36  controls the components. 
         [0037]    The image bearing unit  26  has, for example, four image forming subunits  64  (image forming structures). In each of the image forming subunits  64 , an image bearing body  40  is rotatably supported. The image bearing body  40  bears an image that is transferred to a conveying belt  60  which will be described later or paper transported by the conveying belt  60 . The image bearing body  40  is formed of, for example, a photoreceptor having a photosensitive layer. In the image forming subunit  64 , around the image bearing body  40 , the following are arranged: a charging device  42  with charging rollers for charging the image bearing body  40  with a given polarity, a development device  44  which develops an electrostatic latent image formed on the image bearing body by a developer, an optical charge-erasing device  46  (charge-erasing unit) which removes charges from the image bearing body  40  after transfer, and a cleaning device  48  which eliminates the remaining developer after the transfer of a developer image from the image bearing body  40 . 
         [0038]    The toner boxes  50  are connected laterally to the back side of the image bearing unit  26 . Each toner box  50  is integrally formed of a toner feeder  54  and a toner collector  52 . The toner feeder  54  is connected to the development device  44  and supplies toner to the development device  44 . The toner collector  52  is connected to the cleaning device  48  and collects toner of each color. The toner boxes  50  are, for example, for magenta, yellow, cyan and black. 
         [0039]    Each of the optical projection devices  56  is formed of a laser exposure device and located in a posterior direction to the image bearing unit  26  and in a corresponding position to each image bearing body  40 . The optical projection device  56  irradiates the uniformly charged image bearing body  40  with laser to form a latent image. 
         [0040]    The transfer unit  28  is located in front of the image bearing unit  26  and placed vertically facing the image bearing unit  26 . In the transfer unit  28 , the conveying belt  60  is suspended on two supporting rollers  58  installed in up and down positions. The conveying belt transports an image or paper. Transfer rollers  62  are disposed in abutting contact with the image bearing bodies  40  with the conveying belt  60  running between each transfer roller and each image bearing body. 
         [0041]    Accordingly, after each of the image bearing bodies  40  is charged by the charging device  42 , an electrostatic latent image is formed on the image bearing body by the optical projection device  56 , and this image is made visible with toner by the development device  44 . A toner image formed on each image bearing body  40  is transferred onto paper being transported by the conveying belt  60  in the transfer unit  28  and fixed onto the paper by the fixing device  30 . After the transfer, charges on the image bearing body  40  are removed by the optical charge-erasing device  46 . 
         [0042]      FIG. 2  depicts an image forming subunit  64 , focusing on an image bearing body  40  and an optical charge-erasing device  46 . 
         [0043]    As shown in  FIG. 2 , the optical charge-erasing device  46  includes a light irradiation element  68  and a light emission member  70 . 
         [0044]    The light emission member  70  is a light source provided in the image forming apparatus main body  12  and it is, for example, an LED (Light Emitting Diode). The light emission member  70  is positioned in a line extending in a longitudinal direction of the light irradiation element  68 . A distance between the light emission member  70  and the light irradiation element  68  is, for example, 1 to 3 mm. The light emission member  70  applies light to one end face of the light irradiation element  68  in the longitudinal direction, as indicated by arrow A. 
         [0045]    The light irradiation element  68  is installed in an image forming subunit body  66  along the longitudinal direction of the image bearing body  40  rotatably supported in the image forming subunit body  66 . The light irradiation element  68  uniformly irradiates the image bearing body  40  with light emitted from the light emission member  70 , as indicated by arrow B, thereby removing charges from the image bearing body  40 . 
         [0046]      FIG. 3  depicts the optical charge-erasing device  46 , focusing on the side cross section of the light irradiation element  68  of the present exemplary embodiment. 
         [0047]      FIG. 4  shows the cross section of the light irradiation element  68  when viewed from the light emission member  70 . 
         [0048]    As shown in  FIG. 3  and  FIG. 4 , the light irradiation element  68  includes a cavity  78  through which light passes, a translucent light conduit  76  bordering the cavity  78 , and reflection member  72  for reflecting the light. The cavity  78 , the light conduit  76 , and the reflection member  72  are located along the longitudinal direction of the image bearing body  40 . The cavity  78  terminates at one end at an opening  79  formed at one end of the light conduit  76  in the longitudinal direction. In other words, the cavity  78  is bordered by the opening  79  of the light conduit  76  at one end of the light conduit  76  in the longitudinal direction. 
         [0049]    The light conduit  76  is hollow and has the opening  79  for light to enter, formed on the end face in the longitudinal direction. The light conduit  76  is made by extrusion molding from any of the following: e.g., acrylic resin, polycarbonate resin, polyethylene resin, and ABS resin. The inside diameter of the light conduit  76  is, for example, 3 mm and the outside diameter of the light conduit  76  is, for example, 5 mm. Here, the outside diameter of the light emission member  70  is preferably larger than the inside diameter of the light conduit  76 ; for example, 3 mm or more and preferably 5 mm. 
         [0050]    Of the light conduit  76 , the end face with the opening for light to enter is roughened. Roughness of the end face of the light conduit  76  is, for example, Rz=3 to 15 μm, preferably, Rz=15 μm or more. 
         [0051]    The reflection member  72  is a sheath made from, for example, white resin and covers at least a part of the light conduit  76 . More particularly, the reflection member  72  covers the light conduit  76  along the longitudinal direction, but uncovers a light incident section for incident light to enter the light conduit  76  and a side facing and closer to the image bearing body  40 . The reflection member  72  further has a termination section  74  that covers the other end opposite to the end having the opening  79  for light to enter. 
         [0052]    Accordingly, light emitted from the light emission member  70  passes through the cavity  78  or the inside of the light conduit  76  of the light irradiation element  68  and are reflected by at least one of the light conduit  76  and the reflection member  72 , and irradiate the image bearing body  40 . 
         [0053]    Light energy loss when light passes through the cavity is smaller than that when light passes through the light conduit  76 . Therefore, for the light passing through the cavity, attenuation in the light amount is suppressed as the light travels from the end near the light emission member  70  to the far end opposite to the light emission member  70 . Thereby, it is easy to gain a sufficient amount of light for irradiating the image bearing body  40  even at a far point from the light emission member  70 . 
         [0054]    When the termination section  74  is provided on the opposite end of the light emission member  70 , light is reflected by the termination section  74  and returns, with the result that reflection and transmission are repeated. This increases the amount of light irradiating the image bearing body  40  near the termination section  74 . 
         [0055]    Arrows shown in  FIG. 3  schematizes light reflection or transmission occurring at an interfacial surface of either the light conduit  76  or the reflection member  72 . These arrows do not exactly represent all light pathways in terms of incident angles, reflection angles, and refraction angles. Actually, there occur reflections or transmissions of countless light rays beyond those shown. 
         [0056]      FIG. 5  depicts the reflection member  72  when viewed from the open side facing the image bearing body  40 . 
         [0057]    As shown in  FIG. 5 , the reflection member  72  has an open section facing the image bearing body  40  and protrusions  80  which may be formed in, for example, a protruding boss or convex shape. Plural protrusions  80  are provided on both sides of the open section. A distance L between a line connecting head levels of plural protrusions  80  provided on one side of the open section and a line connecting head levels of plural protrusions  80  provided on the other side of the open section is smaller than the diameter of the light conduit  76 . Hence, when the light conduit  76  is fit in the reflection member  72 , the protrusions  80  support the light conduit  76 . 
         [0058]    Instead of provision of the reflection member  72 , alternative manners may be used in which the outside surface of the light conduit  76  is coated with a coating material having a color with a high reflectivity of light, such as white coating, and in which the outside surface of the light conduit  76  is covered with tape having a color with a high reflectivity of light, such as silver tape. Even in cases where these manners are used, the open section facing the image bearing body  40  remains unmasked. 
         [0059]      FIGS. 6A and 6B  are graphs that represent a relationship between the amount of light irradiating the image bearing body  40  and the distance from the light emission member  70 . 
         [0060]      FIG. 6A  shows a relationship between the amount of light irradiating the image bearing body  40  and the distance from the light emission member  70  in the case of light irradiation using a light guide unit with fine concavo-convex shapes formed in a direction intersecting the longitudinal direction.  FIG. 6B  shows a relationship between the amount of light irradiating the image bearing body  40  and the distance from the light emission member  70  in the case of using the light irradiation element  68  of the present exemplary embodiment. 
         [0061]    When taking a broad view of the graph shown in  FIG. 6A , attenuation in the light amount in the end near the light emission member  70 , the far end (termination section  74 ) opposite to the light emission member  70 , and the intermediate section is smaller than that observed in  FIG. 6B . From a microscopic perspective, due to that fine concavo-convex shapes are formed in a direction intersecting the longitudinal direction of the light guide unit, alternate rise and fall of light irradiation appear more clearly than in  FIG. 6B . 
         [0062]    On the other hand, when taking a broad view of the graph shown in  FIG. 6B , attenuation in the light amount from the end near the light emission member  70  to the termination section  74  is larger than that observed in  FIG. 6A . Because light is reflected in the termination section  74 , the light amount increases from the intermediate section to the termination section  74 . From a microscopic perspective, alternate rise and fall of light irradiation do not appear, because fine concavo-convex shapes are not formed in the light conduit  76  in a direction intersecting the direction along the image bearing body  40 . If fine notched grooves are formed in the light conduit  76  in the direction along the image bearing body  40 , attenuation in the light amount from the end near the light emission member  70  to the termination section  74  will become more moderate in a broad perspective. 
         [0063]    Supposing that the image bearing body  40  has deteriorated over time, a portion exposed to strong light irradiation and a portion exposed to weak light irradiation would have different amounts of charges on the image bearing body  40 . In this case, if the light guide unit relevant to  FIG. 6A  is used, when an image with an intermediate image density such as a halftone image is printed, fine dark and light lines may appear as a defect visible to the human eye, because variations in charge amounts occur in close intervals. On the other hand, in the manner relevant to  FIG. 6B , fine dark and light lines would not appear, showing no defect visible to the human eye, even if an image with an intermediate image density such as a halftone image is printed, because alternate rise and fall of light irradiation do not occur. 
         [0064]    Moreover, the light guide unit relevant to  FIG. 6A  is generally molded by die machining, whereas the light conduit  76  relevant to  FIG. 6B  may be manufactured by simple, less costly processing such as drawing and extruding. Even if the light conduit  76  is manufactured by such processing, fine dark and light lines would not appear due to alternate rise and fall of light irradiation when the image bearing body  40  has deteriorated over time. 
         [0065]    A degree of removing charges from the image bearing body  40  is determined by requirements of the image forming apparatus or the like in which the image bearing body  40  is used. Therefore, provided that at least a desired level of charge removal can be achieved, no special considerations need to be taken in terms of the degree and uniformity of the charge removal and details may be set appropriately. To achieve at least a desired level of charge removal in the longitudinal direction of the image bearing body  40 , the size, light amount, light intensity, etc. of the light emission member  70 , the length, thickness, shape, transparency, etc. of the light irradiation element  68 , the sensitivity, running speed, etc. of the image bearing body  40 , and the length, thickness, shape, transparency, etc. of the cavity  78 , light conduit  76 , and reflection member  72  constituting the light irradiation element  68  may be set respectively. 
         [0066]    Then, the image forming apparatus  10  is further described with regard to second through eighth exemplary embodiments. In the second through eighth exemplary embodiments of the image forming apparatus  10 , various forms of light irradiation elements  68  are used. 
         [0067]      FIGS. 7A through 7F  show cross sectional views of light irradiation elements  68  according to the second through eighth exemplary embodiments. 
         [0068]      FIG. 7A  shows a light irradiation element  68  in which the cavity  78  is defined by the light conduit  76  and the reflection member  72 .  FIG. 7B  shows a light irradiation element  68  in which the cavity  78  is defined by the light conduit  76  having a nearly semicircular cross section and the reflection member  72 .  FIG. 7C  shows a light irradiation element  68  in which the opening  79  of the light conduit  76  is rectangular. 
         [0069]      FIG. 7D  shows a light irradiation element  68  in which plural cavities  78  are defined by the light conduit  76  and the reflection member  72 .  FIG. 7E  shows a light irradiation element  68  in which the cavity  78  is defined by the light conduit  76  having a circular arc cross section and the reflection member  72 .  FIG. 7F  shows a light irradiation element  68  in which the opening of the light conduit  76  is triangular.  FIG. 7G  shows a light irradiation element  68  in which the cavity  78  is defined by the light conduit  76  made of film such as, e.g., PET (Polyethylene Terephthalate) and the reflection member  72 . 
         [0070]    Next, the image forming apparatus  10  is described with regard to a ninth exemplary embodiment. 
         [0071]      FIG. 8  shows a side cross section of a light irradiation element  68  according to the ninth exemplary embodiment. 
         [0072]    As shown in  FIG. 8 , in the light irradiation element  68  of the present exemplary embodiment, the light conduit  76  has a shape such that its inside diameter becomes larger as the distance from the opening  79  for light to enter goes farther along the longitudinal direction. That is, the inside area of the light conduit  76  changes depending on a position in the longitudinal direction and increases as the distance from the light incident end goes farther toward the opposite end. 
         [0073]    Then, the image forming apparatus  10  is described with regard to a tenth exemplary embodiment. 
         [0074]      FIG. 9  shows a side cross section of a light irradiation element  68  according to the tenth exemplary embodiment. 
         [0075]    As shown in  FIG. 9 , in the light irradiation element  68  of the present exemplary embodiment, the light conduit  76  has a shape such that its outside diameter becomes smaller as the distance from the opening  79  for light to enter goes farther along the longitudinal direction. That is, the outside area of the light conduit  76  changes depending on a position in the longitudinal direction and decreases as the distance from the light incident end goes farther toward the opposite end. 
         [0076]    Then, the image forming apparatus  10  is described with regard to an eleventh exemplary embodiment. 
         [0077]      FIG. 10  shows a cross section of a light conduit  76  in a light irradiation element  68  according to the eleventh exemplary embodiment. 
         [0078]    As shown in  FIG. 10 , in the light irradiation element  68  of the present exemplary embodiment, the outer circumference of the light conduit  76  is provided with plural flutes (grooves). The inner circumference of the light conduit  76  may be provided with such grooves. That is, the light conduit  76  has grooves formed in the longitudinal direction on one of its outer and inner circumferential surfaces. 
         [0079]    Then, the image forming apparatus  10  is described with regard to a twelfth exemplary embodiment. 
         [0080]      FIG. 11  depicts an optical charge-erasing device  46 , focusing on the side cross section of a light irradiation element  68  according to the present exemplary embodiment. 
         [0081]    As shown in  FIG. 11 , in the present exemplary embodiment, the light emission member  70  is covered with a shielding member  83  having an inside diameter larger than the outside diameter of the light conduit  76 . The shielding member  83  extends from the light emission member  70  to at least a middle point of the gap between the light emission member  70  and the light conduit  76 . The shielding member  83  may be a part of the image forming apparatus main body  12 . 
         [0082]    Then, the image forming apparatus  10  is described with regard to a thirteenth exemplary embodiment. In the thirteenth exemplary embodiment of the image forming apparatus  10 , a light irradiation element  68  includes a light conduit  76  provided with convex spots for reflecting light. 
         [0083]      FIG. 12  depicts an optical charge-erasing device  46 , focusing on the side cross section of a light irradiation element  68  according to the thirteenth exemplary embodiment. 
         [0084]      FIG. 13  is an enlarged view of a section surrounded by dotted lines in  FIG. 12 . 
         [0085]    As shown in  FIG. 12  and  FIG. 13 , the light irradiation element  68  includes a cavity  78  through which light emitted from the light emission member  70  passes in a direction intersecting the direction in which the image bearing body  40  turns, a translucent light conduit  76  surrounding at least a part of the cavity  78  and bordering the cavity  78 , and a reflection member  72  to reflect light, provided in sides not facing the image bearing body  40 . 
         [0086]    More specifically, the light conduit  76  includes a cylindrical light conduit body  82  with a predetermined thickness α, convex spots  84  on the outer circumference of the light conduit body  82 , and convex spots  86  on the inner circumference of the light conduit body  82 . There are plural convex spots  84 ,  86  along the direction intersecting the direction in which the image bearing body  40  turns. The convex spots  84 ,  86  may be formed generally annularly or formed helically along the outer circumference or the inner circumference. There are more convex spots  84 ,  86  in a portion including the other end than in a portion including the end for light to enter. That is, there are more convex spots  84 ,  86  near the termination section  74  which will be described later rather than near the opening  79 . 
         [0087]    Although the light conduit body  82 , convex spots  84 , and convex spots  86  have been described as separate components of the light conduit  76 , the light conduit body  82 , convex spots  84 , and convex spots  86  may be formed integrally. For example, when the light conduit  76  is molded by extrusion molding or drawing molding, the conduit may be formed to have a partially wavy shape with a variation in the outside diameter and the inside diameter by changing the drawing speed or extrusion speed or applying vibration. 
         [0088]    Accordingly, as indicated by arrows in  FIG. 12 , light emitted from the light emission member  70  passes through the cavity  78  or the inside of the light conduit  76  of the light irradiation element  68  and is reflected and diffused by at least any of the light conduit body  82 , the interfacial surfaces of the convex spots  84 ,  86 , and the reflection member  72  of the light conduit  76 , and irradiates the image bearing body  40 . 
         [0089]    Here, as indicated by the arrows in  FIG. 12 , for light passing through the cavity  78  and reflected by a concave spot between convex spots  86 , some stays near the concave spot and some is reflected backward toward the light emission member  70 . Because of light reflection occurring in this way, the amount of reflected light increases. Likewise, for light passing through the light conduit  76  and reflected by the inner surface of the light conduit  76  in a convex spot  84 , which is, however, not shown, some stays on the inner surface of the light conduit  76  in the convex spot  84  and some is reflected backward toward the light emission member  70 , and consequently the amount of reflected light increases. 
         [0090]    Furthermore, as indicated by arrows in  FIG. 13 , near a convex spot  84 , the inner surface of the light conduit  76  in a concave spot between convex spots  86  is convex when viewed from the inside of the light conduit  76 . In this section, the passage of the light conduit  76  bulges because of this convex and the convex spot  84 . Thereby, more light stays here and the amount of reflected light increases. Thus, the amount of reflected light builds up by some of light reflected by a concave spot between convex spots  86 , some of light reflected by the inner surface of the light conduit  76  in a convex spot  84 , and light staying in a bulge portion of the passage of the light conduit  76 . 
         [0091]      FIGS. 14A and 14B  are graphs that represent a relationship between the amount of light irradiating the image bearing body  40  and the distance from the light emission member  70 . 
         [0092]      FIG. 14A  is the same as  FIG. 6A .  FIG. 14B  shows a relationship between the amount of light irradiating the image bearing body  40  and the distance from the light emission member  70  in the case of using the light irradiation element  68  of the present exemplary embodiment. In  FIG. 14B , a solid line shows the above relationship for the light irradiation element  68  of the present exemplary embodiment and a dashed line shows the above relationship for alight conduit without the convex spots  84 ,  86 . As shown in  FIG. 14B , the light irradiation element  68  of the present exemplary embodiment has smaller attenuation in the light amount than a light conduit without the convex spots  84 ,  86 . 
         [0093]    Then, the image forming apparatus  10  is described with regard to fourteenth through seventeenth exemplary embodiments. In the fourteenth through seventeenth exemplary embodiments of the image forming apparatus  10 , various forms of light irradiation elements  68  are used. 
         [0094]      FIG. 15  shows a side cross section of a light irradiation element  68  according to a fourteenth exemplary embodiment of the invention. 
         [0095]    As shown in  FIG. 15 , the light irradiation element  68  of the present exemplary embodiment includes a light conduit  76  in which the light conduit body  82  is only provided with convex spots  84 . That is, convex spots  86  are not provided. Due to this, the outside of the light conduit  76  has a concavo-convex configuration along the longitudinal direction. 
         [0096]      FIG. 16  shows a side cross section of a light irradiation element  68  according to a fifteenth exemplary embodiment of the invention. 
         [0097]    As shown in  FIG. 16 , the light irradiation element  68  of the present exemplary embodiment includes a light conduit  76  in which the light conduit body  82  is only provided with convex spots  86 . That is, convex spots  84  are not provided. Due to this, the inside of the light conduit  76  has a concavo-convex configuration along the longitudinal direction. 
         [0098]      FIG. 17  is an enlarged view of a part of a side cross section of a light irradiation element  68  according to a sixteenth exemplary embodiment of the invention. 
         [0099]    As shown in  FIG. 17 , the light irradiation element  68  of the present exemplary embodiment includes a light conduit  76  in which a convex spot  84  is provided with reflecting grooves  90 . That is, the outside of the light conduit  76  is provided with the reflecting grooves  90 . The reflecting grooves  90  are made along the direction intersecting the longitudinal direction of the light conduit  76 . The reflecting grooves  90  may be made generally annularly or made helically. Plural reflecting grooves  90  are made. In particular, there are more grooves in the upper part of the convex spot  84 . Depth of the reflecting grooves  90  is a value to an extent that the grooves do not reach the light conduit body  82 . 
         [0100]    The reflecting grooves  90  may be provided in the light irradiation element  68  ( FIG. 15 ) according to the fourteenth exemplary embodiment. Although the reflecting grooves  90  are visibly notched to a depth in  FIG. 17 , they may be so fine as to be invisible. For example, the reflecting grooves  90  may be made by filing down the outside surface or by rolling the light irradiation element  68  on a rough surface. 
         [0101]      FIG. 18  is an enlarged view of a part of a side cross section of a light irradiation element  68  according to a seventeenth exemplary embodiment of the invention. 
         [0102]    As shown in  FIG. 18 , the light irradiation element  68  of the present exemplary embodiment includes a light conduit  76  in which a convex spot  86  is provided with reflecting grooves  92 . That is, the inside of the light conduit  76  is provided with the reflecting grooves  92 . The reflecting grooves  92  are made along the direction intersecting the longitudinal direction of the light conduit  76 . The reflecting grooves  92  may be made generally annularly or made helically. Plural reflecting grooves  92  are made. In particular, there are more grooves in the upper part of the convex spot  86 . Depth of the reflecting grooves  90  is a value to an extent that the grooves do not reach the light conduit body  82 . The reflecting grooves  90  may be provided in the light irradiation element  68  ( FIG. 13 ) according to the thirteenth exemplary embodiment and the light irradiation element  68  ( FIG. 17 ) according to the sixteenth exemplary embodiment. 
         [0103]    Then, the image forming apparatus  10  is described with regard to eighteenth and nineteenth exemplary embodiments. In the eighteenth and nineteenth exemplary embodiments of the image forming apparatus  10 , a light irradiation element  68  includes a reflection member  72  having a light reflecting surface  98  made of a metal film as its inner wall. 
         [0104]      FIG. 19  depicts an optical charge-erasing device  46 , focusing on the side cross section of a light irradiation element  68  according to an eighteenth exemplary embodiment. 
         [0105]      FIG. 20  shows an A-A cross section of the light irradiation element  68  according to the eighteenth exemplary embodiment used in the image forming apparatus. 
         [0106]    As shown in  FIG. 19  and  FIG. 20 , in the reflection member  72  of the light irradiation element  68 , a light reflecting surface  98  is formed as the inner wall made of a thin metal film with light reflectivity. The inner wall that is the light reflecting surface  98  covers all over the inside of light irradiation element  68  except for a light outlet  94  so that incident light from the opening  79  does not leak out from any part other than the light outlet  94 . In the middle of the light irradiation element  68  in an axial direction, a light guide passage  100  (light guide passage body) is formed as a cylindrical structure. The light guide passage  100  is formed from a highly translucent material such as, e.g., methacrylic resin, polycarbonate resin, cyclic olefin resin, or glass. 
         [0107]    Inside the resin that forms the light guide passage  100 , light diffusive particles  96  having light diffusivity such as aluminum trioxide and titanium dioxide are dispersed evenly. 
         [0108]    By configuring the light irradiation element  68  in this way, the light irradiation element  68  takes in light from the light emission member  70  through the opening  79  and allows the light to travel in a straight line through the light guide passage  100 . The light irradiation element  68  converts the light traveling in a straight line into light to travel in different directions by making the light reflected by the light diffusive particles  96  dispersed in the light guide passage  100 . This light is reflected by the light reflecting surface  98  covering the inside wall of the reflection member  72  and light to travel in more different directions is produced. By emitting light dispersed in diverse directions from the light outlet  94  toward the image bearing body  40 , removing charges from the image bearing body  40  is performed with a uniform amount of light. 
         [0109]    The light reflecting surface  98  may be provided as described below. To obtain a sufficient amount of reflected light from the light reflecting surface  98 , the reflectivity of the light reflecting surface  98  may be 40% or higher. By setting the reflectivity at 40% or higher, it can be avoided that the amount of light across the light guide passage  100  becomes nonuniform, as the light amount is larger near the light incident end, whereas the light amount decreases as the light travels and comes nearer to the opposite end. Uniform light irradiation can be accomplished for the image bearing body  40  with the length of the axis (about 300 mm) for A3 size. 
         [0110]    The light reflecting surface  98  may be produced by forming a thin metal film of aluminum or the like on the inner wall of the reflection member  72  of the light irradiation element  68  by a vacuum deposition method. Alternatively, the light reflecting surface  98  may be produced as a thin metal film directly printed on the inner wall of the reflection member  72  of the light irradiation element  68  by screen printing or hot offset printing. The light reflecting surface  98  may be produced as a seal member having light reflectivity covered on the inner surface of the reflection member  72 . Furthermore, to provide reflectivity, for example, the reflection member itself may be made of a metal material with reflectivity. In short, the wall surface may have light reflectivity and there is no limitation on its material, manufacturing method, etc. 
         [0111]    Then, the light diffusive particles  96  may be provided as described below. The refraction factor of the light diffusive particles  96  used in the present exemplary embodiment may be 1.7 to 1.8 for aluminum trioxide. If the refraction factor is less than 1.7, light scattering is so small that light traveling in a straight line is unhampered and reaches the other end opposite to the opening  79 . It is hard to alter this light to that directed to face the image bearing body  40 . Conversely, if the refraction factor exceeds 3.0, light scattering is too large. Excessive light scattering occurs near the opening  79 , whereas a sufficient amount of light is not transmitted to the end opposite to the opening  79 , and the amount of light is liable to be uneven. While the refraction factor of the light diffusive particles  96  is specified as 1.7 to 1.8 in the present example, it may be 1.7 to 2.0 or 1.7 to 2.5. Even with 1.7 to 3.0, a desired effect can be obtained. 
         [0112]    The average particle size of these particles may be 0.01 to 1.0 μm. If the average particle size exceeds 1.0 μm, reflected light in the axial direction of the light guide passage  100  increases to block the light traveling in a straight line from the opening  79 . This results in loss in the total amount of light, which is undesirable. If the average particle size is less than 0.01 μm, incident light cannot be scattered and the intended role of light diffusion is hard to fulfill. 
         [0113]    Furthermore, the quantity of the particles may be 1 to 200 ppm relative to the weight of the resin. If this quantity is less than 1 ppm, the proportion of light reflected by the light diffusive particles  96 , while traveling in a straight line from the opening  79 , is too small. This makes it difficult to obtain the effect of light diffusion. Conversely, when the quantity of the particles exceeds 200 ppm, most of incident light from the opening  79  only scatters near the opening  79 . This may prevent a sufficient amount of light from reaching a point near the opposite end from the middle of the light guide passage  100 . 
         [0114]    Although an appropriate proportion of the particles in the resin weight is specified as 1 to 200 ppm in the above description, the particles throughout the passage do not need to exist at an equal proportion. In the light guide passage  100 , the particles may exist, for example, at a rate of 1 to 10 ppm near the opening  79 , at a rate of 5 to 40 ppm in the middle, and at a rate of 10 to 70 ppm near the end opposite to the opening  79 . In this way, by setting the quantity of the particles adaptive to increase/decrease in the amount of light depending on distance from the opening  79 , a uniform amount of light can be obtained throughout the light guide passage  100 . 
         [0115]    The shape of the particles may be completely spherical, spherical, scale-like, cubic, or in an indeterminate form. The particle shape may be any combination of diverse shapes and is not restrictive. Further, although aluminum trioxide and titanium dioxide have already been mentioned as the light diffusive particles used in the present exemplary embodiment, any particles that meet the conditions described above may be used, not restricted to the above-mentioned ones. 
         [0116]    In this way, light from the light emission member  70  travels in a straight line from the opening  79  through the light guide passage  100  in the axial direction of the light irradiation element  68  and the light is reflected in diverse directions by the light diffusive particles  96  dispersed in the passage. This light is also reflected by the light reflecting surface  98  covering the inner wall of the reflection member  72  and this creates more even scattering of the light, with the result that the amount of light becomes uniform anywhere in the passage. The light is emitted from the light outlet  94  and irradiates the image bearing body  40 . Thereby, sufficient removal of charges can be performed, avoiding that the charge removal effect varies with position on the image bearing body. 
         [0117]      FIG. 21  depicts an optical charge-erasing device  46 , focusing on the side cross section of a light irradiation element  68  according to a nineteenth exemplary embodiment. 
         [0118]    As shown in  FIG. 21 , in the image forming apparatus  10  of the present exemplary embodiment, both ends of the light irradiation element  68  are open and light emission members  70  are provided beside both ends of the light irradiation element  68 . Thereby, the proportion of the light diffusive particles  96  relative to the resin weight can be reduced by half. Incident light enters the light guide passage  100  from both ends and this can provide more uniform light and a sufficient amount of light. It is thus possible to avoid deficient removal of charges due to an insufficient amount of light. By provision of the light emission members  70  beside both ends of the light irradiation element  68 , a sufficient amount of light can be gained even with reduction by half in the amount of incident light at each end. 
         [0119]    Since the light diffusive particles cause light scattering in diverse directions, the shape of the light irradiation element  68  may not be cylindrical in the axial direction of the image bearing body. For example, as shown in  FIG. 22 , the light irradiation element  68  may be formed in the shape of a rectangular solid. Alternatively, as shown in  FIG. 23 , the light irradiation element  68  may be formed in the shape of convex quadrilateral with the region of the light outlet  94  being narrowed. In the latter case, because the angle of light emission can be wider, the time of light irradiation onto the image bearing body  40  becomes longer than otherwise and more sufficient removal of charges can be performed. Thus, the shape of the light irradiation element  68  can be diversified and the degree of freedom in design increases, for example, installing the light irradiation element  68  closer to the image bearing body than ever before. 
         [0120]    The present invention may be embodied in other specific forms without departing from its spirit or characteristics. The described exemplary embodiments are to be considered in all respects only as illustrated and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.