Abstract:
A novel optical irradiation apparatus includes a light source and a light guide. The light source is configured to radially irradiate a light beam. The light guide is configured to include a transparent material configured to lead the light beam irradiated from the light source in a specific direction and to emit the light beam. The light guide also includes an incidence plane, an exit plane, and plural connecting planes. The incidence plane is configured to receive the light beam. The exit plane is configured to emit the light beam to so as to irradiate an object. The plural connecting planes are configured to connect the incidence plane to the exit plane. A part of at least one of the plural connecting planes is inclined with respect to an axis of the light beam.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical irradiation apparatus, an image reading apparatus, and an image forming apparatus. More particularly, the present invention relates to an apparatus having a light guide which is made of a transparent material and is capable of causing light that enters the light guide from a light source-to exit the light guide in a specific direction.  
         [0003]     2. Discussion of the Background  
         [0004]     A conventional optical irradiation apparatus is used as an optical irradiator that irradiates a manuscript in an image reading apparatus, such that a reflecting image of the manuscript is read by using, for example, a photo acceptance element such as a charge coupled devices (CCD), a complementary metal oxide semiconductor (CMOS), etc. In a case an image reading apparatus reads a color image, light reflecting from the manuscript is generally received by individual photo acceptance elements in colors of red (R), green (G), and blue (B).  FIG. 1A  illustrates light reflecting from the manuscript to the CCD. The figure includes a manuscript M, a first mirror  19 , a second mirror  20 , a third mirror  21 , an image formation lens  16 , and a CCD  17 . As shown in  FIG. 1A , each photo acceptance element corresponding to each color is arranged so that the positions may differ from each other. Therefore, the received light on each photo acceptance element includes the light reflected from various points of the manuscript. Then, in a direction (i.e., a horizontal direction in  FIG. 1A ) of the manuscript corresponding to a direction of a row of the photo acceptance elements, it is necessary to improve the quality of reading the image that the intensity of the light be evenly irradiated from the optical irradiation apparatus. Specifically, w and b are defined as shown in  FIG. 1B , where w is a width of each photo acceptance element (in the direction of a row of photo acceptance elements), and b is a distance between the center of the photo acceptance element. p, as used below, is a reduction ratio by the optical system from the manuscript to each photo acceptance element. A width X on the manuscript, which needs to be irradiated with evenly intense light (in the horizontal direction in  FIG. 1B ), is set to (w+bx2+v)/p. “v” is a parameter suitably set in consideration of errors, such as a manufacture error.  
         [0005]     In order to irradiate a width X of the manuscript with evenly intense light, for example, an apparatus using a cylinder type xenon lamp as a light source which is arranged so that its longitudinal direction may intersect perpendicularly to the direction of the width X is used as the optical irradiation apparatus. However, in recent years, there has been a demand to save energy and increase the reliability of the image reading apparatus. The xenon lamp consumes a lot of power and the calorific value is great. Therefore, a light source with smaller power consumption and calorific value than the xenon lamp is desired. As such, for example, a light emitting diode (LED) may be used as the light source. However, compared with the xenon lamp, the optical irradiation intensity of the LED is generally small. Therefore, if the LED is simply used as the light source, it is difficult to irradiate light with a sufficient intensity in the width X on the above-mentioned manuscript.  
         [0006]     The conventional optical irradiation apparatus, which has a transparent light guide between a light source and a manuscript, is known. The light guide leads the light from the LED toward the manuscript. If the optical irradiation apparatus equipped with such a light guide is used, it becomes possible to concentrate the radial light from the LED to the narrow domain of the width X on the above-mentioned manuscript. Therefore, if the light guide is used, even if the LED that has a small irradiation intensity etc. is used as the light source, it becomes possible to irradiate light with large intensity at the portion of the width X.  
         [0007]     If the LED which irradiates light radially is used as light source, in order to concentrate the light in the portion (irradiation target domain) of the width X on the manuscript for intensifying the light in the target domain, it is important to lead the incident light with the light guide as much as possible to the exit plane of the light guide. In order to realize this, it is necessary to prevent the incident light from exiting the light guide before the light reaches the exit plane.  
         [0008]      FIG. 2  illustrates incident light entering the light guide. This figure is seen from the direction which intersects perpendicularly to the width X on the above-mentioned manuscript shown in  FIG. 1A .  
         [0009]     Although a part of the incident light, which entered from an incidence plane  431   a  of a light guide  431 , may pass through the light guide to an exit plane  431   b,  much of the light reaches a connecting plane  431   c  first. According to incidence angles (angle with the normal line of the connecting plane  431   c ) θ 1  and θ 2  to the connecting plane  431   c,  a part of the light penetrates the connecting plane  431   c.  For example, an incidence light L 1  does not penetrate the connecting plane  431   c.  The connecting plane  431   c  reflects the light as L 1 ′, and a part of an incident light L 2  penetrates the connecting plane  431   c  as L 2 ′. In detail, the incident light L 2  with the incidence angle θ 2  smaller than a critical angle α to the connecting plane  431   c  penetrates and exits through the connecting plane  431   c  to the outside as L 2 ′, and the incidence light L 1  with the incidence angle θ 1 , which is equal to or larger than the critical angle α, to the connecting plane  431   c  reflects on the connecting plane  431   c  as L 1 ′ and finally exits from the exit plane  431   b.    
         [0010]      FIG. 3  shows a conventional optical irradiation apparatus capable of preventing the incident light from exiting from the light guide before the light reaches the exit plane of the light guide.  
         [0011]     In the conventional optical irradiation apparatus, as shown in  FIG. 3 , which has an LED  32  as light source and an incidence plane  531   a  of a light guide  531  that is formed in a convex shape so that it makes the incidence angle to a connecting plane  531   c  greater than the incidence angle when compared to when the incidence plane is flat. This conventional optical irradiation apparatus prevents the incident light from the incidence plane  531   a  from passing through the connecting plane  531   c  to the outside, by reflecting the light incident on the connecting plane  531   c.  If the incidence plane is flat, the incidence angle to the connecting plane  531   c  is smaller than the critical angle, so that the light may penetrate the connecting plane  531   c  to the outside of the light guide.  
         [0012]     Further, in the above-mentioned conventional optical irradiation apparatus, a reflective part  533  is formed by vapor-depositing aluminum on the external surface of the connecting plane  531   c.  The incident light which pass through the connecting plane  531   c  to outside, even if the incidence plane  531   a  is formed in the shape of convex, t may be returned to the inside of the light guide because the light reflects on the reflective part  533 .  
         [0013]     Thus, in the above-mentioned conventional optical irradiation equipment, by forming the incidence plane  531   a  of the light guide  531  in a convex shape, and forming the reflective part  533  on the external surface of the connecting plane  531   c,  the conventional optical irradiation equipment prevents the incident light from passing through the incidence plane  531   a  and exiting to the outside of the light guide before the light reaches the exit plane of the light guide.  
         [0014]     However, since it is difficult to manufacture the incidence plane  531   a  of the light guide  531  in a convex shape compared to a flat incidence plane, the manufacturing costs of the convex shaped incidence plane are high. In addition, if the reflective part  533  is formed on the external surface of the connecting plane  531   c,  additional costs are incurred for the reflective material, and process affixing the reflective part  533  to the external surface of the connecting plane  531   c.  Therefore, the manufacturing costs of the conventional irradiation apparatus are high. Thus, in the above-mentioned conventional optical irradiation apparatus, although it may prevent the incident light from exiting through the incidence plane  531   a  to the outside of the light guide before the light reaches the exit plane of the light guide, there is a problem that the manufacturing cost is high.  
       SUMMARY OF THE INVENTION  
       [0015]     Non-limiting embodiments of a novel optical irradiation apparatus which can effectively lead an incidence light irradiated from the light source to a specific direction is described herein.  
         [0016]     In one example, a novel optical irradiation apparatus includes a light source and a light guide. The light source is configured to radially irradiate a light beam. The light guide is configured to include a transparent material configured to lead the light beam irradiated from the light source in a specific direction and to emit the light beam. The light guide also includes an incidence plane, an exit plane, and plural connecting planes. The incidence plane is configured to receive the light beam. The exit plane is configured to emit the light beam to so as to irradiate an object. The plural connecting planes are configured to connect the incidence plane to the exit plane. A part of at least one of the plural connecting planes is inclined with respect to an axis of the light beam.  
         [0017]     In another example, a novel optical irradiation apparatus includes a light source and a light guide. The light source is configured to radially irradiate a light beam. The light guide is configured to include a transparent material configured to lead the light beam irradiated from the light source in a specific direction and to emit the light beam. The light source and the light guide are provided on a single positioning member. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     A more complete appreciation of the non-limiting embodiments described in the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0019]      FIG. 1A  is an illustration of light reflecting from a manuscript to a CCD;  
         [0020]      FIG. 1B  is an illustration of a configuration of photo acceptance elements of the CCD;  
         [0021]      FIG. 2  is an illustration of a light path in a light guide;  
         [0022]      FIG. 3  is an illustration of a conventional optical irradiation apparatus;  
         [0023]      FIG. 4  is an exemplary configuration of a full color copying apparatus in accordance with an exemplary embodiment of the present invention;  
         [0024]      FIG. 5  is illustrates a general configuration of an optical irradiation unit which is seen from a horizontal direction included in the full color copying apparatus of FIG.  4 ;  
         [0025]      FIG. 6A  is a perspective illustration of the optical irradiation unit for an exemplary embodiment;  
         [0026]      FIG. 6B  is a perspective illustration of the optical irradiation unit for another exemplary embodiment;  
         [0027]      FIG. 6C  is a perspective illustration of the optical irradiation unit for another exemplary embodiment;  
         [0028]      FIG. 6D  is a perspective illustration of the optical irradiation unit for another exemplary embodiment;  
         [0029]      FIG. 7A  is an illustration of a light path in a light guide for an exemplary embodiment;  
         [0030]      FIG. 7B  is an illustration of a light path in a light guide for another exemplary embodiment;  
         [0031]      FIG. 8  is an illustration of a distribution of light exiting from an LED;  
         [0032]      FIG. 9  is an illustration of a configuration of an optical irradiation unit for an exemplary embodiment; and  
         [0033]      FIG. 10  is an illustration of a configuration of an optical irradiation unit for another exemplary embodiment. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0034]     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 4  is an elevational view showing an outline of an internal structure of a full color copying machine  1  which is an exemplary image forming apparatus to which this invention is applied.  
         [0035]     Although the color copying machine is mentioned as an example, the present invention is equally applicable when applied to a black and white copying machine. A printer engine  3  for forming a color image is provided in the central part of a main part  2  of copying machine  1 . This printer engine  3  is equipped with four drum shaped photo conductors  4  which are arranged at equal intervals and provided in parallel. The printer engine  3  is equipped with four electrification rollers  5  to uniformly charge in the perimeter side of each photo conductor  4 , respectively. The printer engine  3  is equipped with the exposure device  6  which forms an electrostatic latent image in the perimeter side of each photo conductor  4  by exposing the perimeter side of each photo conductor  4  charged with each electrification roller  5 , respectively, according to the corresponding image data. In addition, the printer engine  3  includes four developers  7 , a middle transfer belt  8 , four cleaning devices  9 , and a transfer roller  10 . The developers  7  develop from electrostatic latent image to a toner image by supplying toner to the electrostatic latent image on the perimeter side of each photo conductor  4 . The toner image is transferred to the middle transfer belt  8  from each photo conductor  4 . The cleaning device removes the remaining toner on each photo conductor  4  after the toner is transferred to the middle transfer belt  8 . The transfer roller  10  transfers the toner image on the middle transfer belt  8  to a recording paper S. On the four photo conductors  4 , the toner image of different colors (Y; yellow, M; magenta, C; cyan, K; black), respectively is formed, by being transferred one by one so that the toner images of each of these colors may overlap mutually on the middle transfer belt  8 . Then, a toner image of color is formed on the middle transfer belt  8 . Finally, the color toner image is formed on the recording paper S.  
         [0036]     A scanner, as an image reading part, reads the image of a manuscript side that is provided on the upper part of the main part  2  of the apparatus. The scanner includes an automatic document feeder (ADF)  11 , a contact glass  12 , and an image read mechanism  13  as an image reading unit. The ADF  11  automatically conveys the manuscript D to which the light is illuminated with the optical irradiation equipment mentioned later. The manuscript D is put on the contact glass  12 . The image read mechanism  13  reads the image of the manuscript D on the contact glass  12 .  
         [0037]     The image read mechanism  13  includes a first running unit  14 , a second running unit  15 , an image formation lens  16 , and a CCD  17  which is a photoelectric conversion element as a photo acceptant element. The first running unit  14  and the second running unit  15  run at the speed rate of 2:1 in parallel with the contact glass  12 . An optical irradiation unit  18  and a first mirror  19  are provided in the first running unit  14 . The manuscript D which is put or conveyed by the ADF  11  on to the contact glass  12  is illuminated from the lower part of contact glass  12  by the optical irradiation unit  18 . The first mirror  19  reflects the reflected light from the manuscript to the CCD  17 . The second running unit  15  includes a second mirror  20  and a third mirror  21  which reflect the reflected light from the first mirror  19 . The reflected light through the first mirror  19 , the second mirror  20 , the third mirror  21  and the image formation lens  16  is accepted on the CCD  17 .  
         [0038]     In the lower part of the main part  2  of the machine, paper cassettes  22  are provided which contain the recording paper S. A pickup roller  23  and a feed roller  24  separate and feed the recording paper S one by one. And the recording paper S is conveyed along paper conveyance way  25  prepared in the main part  2  of the machine. Along the paper conveyance way  25 , a resist roller  26 , a transfer roller  10 , a fixing unit  27 , and a delivery roller  28  are arranged. The resist roller  26  is driven so that the recording paper is held temporarily and conveyed to a second transferring region at a same time with the toner image that come into the second transferring region between the middle transfer belt  8  and the transfer roller  10 . After the second transferring, the recording paper S is conveyed to the fixing unit  27 , and the toner is melted and fixed on the recording paper S with heat and pressure by the fixing unit  27 . After fixing, the recording paper S is delivered on a paper output tray  29  by the delivery roller  28 .  
         [0039]     Next, configuration of the optical irradiation unit  18  of the above-mentioned image reading part is explained.  FIG. 5  is an illustration showing a general configuration of the optical irradiation unit  18  which is seen from about the horizontal direction that intersects perpendicularly to the running direction of the 1st running unit  14 .  
         [0040]      FIG. 6A  is a perspective illustration of the above-mentioned optical irradiation unit  18 . As shown in  FIG. 6A , the optical irradiation unit  18  in this embodiment has plural LEDs  32 , which are the light sources arranged at one sequence on an LED array board  30  which is a circuit board, and a light guide  31 . The LED array board  30  is arranged so that its longitudinal direction, which intersects perpendicularly to the running direction of the first running unit  14 , extends to the main scanning direction of the manuscript D. The LEDs  32  are arranged along the longitudinal direction of the LED array board  30 . A circuit pattern and the various circuit elements for supplying electric power to LEDs  3 , which are not illustrated, are formed in the LED array board  30 . The LEDs  32 , in this embodiment, are arranged on the LED array board  30  so that the exit side may face and be parallel to the substrate side of the LED array board  30 . Therefore, the direction of a central line of the light which exits from the exit side of the LEDs  32  is almost in parallel with the substrate side of the LED array board  30 . In addition, although the LEDs  32  are arranged in one sequence in this embodiment, other embodiments may arrange the LEDs in two or more sequences.  
         [0041]     The light guide  31  is made of a translucent material which has optical permeability, for example, transparent resin (acrylics, polycarbonate, etc.), glass, etc. The light guide  31  is a hexahedron object which has incidence plane  31   a  of the long shape of a rectangle, at least longer than the length of one or more sequences of LEDs  32 , and an exit plane  31   b.  The light guide  31  is arranged between each LED  32  and the manuscript. Specifically, the light guide  31  is arranged so that the incidence plane  31   a  may face each exit plane of LED  32 , and the incidence plane  31   a  may be near or in contact with the exit plane of LED  32 . The light guide  31  is also arranged so that the exit plane  31   b  may face the manuscript. Then, the light guide  31  accepts the light irradiated from LED  32  through its incidence plane  31   a,  guides and outputs the light to the manuscript from the exit plane  31   b.  In this embodiment, the light guide  31  is attached with, for example, adhesives, double-stick tape, etc. to the substrate side of the LED array board  30  in which plural LEDs  32  are attached.  
         [0042]     The two connecting planes at the edge of longitudinal direction of the light guide  31 , between the planes of  31   a  and  31   b,  are vertical to the connecting plane on the substrate side of the LED array board  30 . On the other hand, a normal line of a connecting plane  31   c  which faces the connecting plane attached on the substrate is not vertical to the substrate side of the LED array board  30 . In detail, the distance between the connecting plane  31   c  and the connecting plane on the substrate may enlarge toward the exit plane  31   b  from the incidence plane  31   a.  Then, a cross section of the light guide  31  may form a trapezoid. The incidence plane  31   a  corresponds to the short side of the trapezoid and the exit plane  31   b  corresponds to the long side of the trapezoid.  
         [0043]     As for a method of manufacturing the light guide  31  of this embodiment, it is preferable to adopt a resin mold process which fills up a metallic mold with the resin which has optical requisite permeability, because the light guide  31  has long shape as shown in  FIG. 6A . Since it is necessary to take out the fabricated resin from the metallic mold when manufacturing by this method, it is preferable that the light guide have a form which is easy to extract from the metallic mold, which will lower manufacturing costs. The light guide  31  has no dent place on the connecting planes except for the connecting planes  31   a  and  31   b.  Dent place refers to a concave potion. Therefore, in manufacturing the light guide  31  using a metallic mold, the resin in the metallic mold can be easily taken out from the metallic mold by taking out from the exit plane  31   b  side of the light guide  31 .  
         [0044]     In this embodiment as shown in  FIG. 5 , the LED  32  and the light guide  31  are so arranged that the direction of the light output from the exit plane  31   b  is about parallel with the side of the LED array board  30 . The light from the exit plane  31   b  may spread radially because the light is output radially from the exit plane of the LED  32 . In positioning the light guide  31  with respect to the LED array board  30 , the certainty of the positioning increases by arranging the whole light guide  31  on the substrate side of the LED array board  30 . However, if the light guide  31  is attached to the LED array board  30  so that the exit plane  31   b  is located on the substrate side of the LED array board  30 , a part of light output from the exit plane  31   b  will be interrupted by the LED array board  30 . Consequently, the interrupted light is not irradiated to the manuscript. Since LED  32 , which has comparatively small optical intensity is adopted, it is preferable that the radial light from the exit plane  31   b  be collected on the specific part of the manuscript, for example, the width X on the manuscript as shown in  FIG. 1A , if possible. Therefore, it is desirable to arrange the light guide  31  so that a part of the light which is output from the exit plane may not be interrupted by the LED array board  30 . Then, in the embodiment as shown in  FIG. 5 , the light guide  31  is so arranged that the exit plane  31   b  is on the edge of the LED array board  30  or extends past the edge of the LED array board. Consequently, the light which is output from the exit plane  31   b  is not interrupted by the LED array board  30 . As a result, all the light which is output from the exit plane  31   b  may be irradiated to the manuscript.  
         [0045]     Furthermore, the light guide  31  has a configuration that all light from each LED  32  can enter the incidence plane  31   a,  since the incidence plane  31   a  may face each exit plane of LED  32 , and be near or in contact with the exit plane of LED  32 . In an exemplary embodiment with this configuration, as for the LED, it is desirable that the LED exit plane have a flat or concave shape. If the exit plane of the LED has a convex shape, it is necessary to form the light guide  31  so that the convex shaped exit plane can be covered. This increases the manufacturing costs of the light guide  31 . Furthermore, if a lead of LED  32  is over the exit plane to the light guide  31 , the lead may interrupt the arrangement of the light guide  31  so that the incidence plane  31   a,  that faces each exit plane of LED  32 , is not near or in contact with the exit plane of LED  32 . Therefore, it is desirable to arrange each lead of LED  32  so that it is in a position distant from the light guide  31 , and not in a position near each exit plane of LED  32 .  
         [0046]      FIG. 6B  is a perspective illustration of an optical irradiation unit  118  of another embodiment of the present invention. A light guide  131  is made of one piece including an attachment part  131   c  near an incidence plane  131   a.  The incidence plane  131   a  is almost vertical to the side of the attachment part  131   c.  The LED array board  30  is attached with, for example, adhesives, double-stick tape, etc. on this attachment part  131   c.    
         [0047]     In the exemplary embodiment shown in  FIG. 6B , the exit plane of each LED has the same position of an edge side of the LED array board  30 . The edge side of the LED array board  30  touches the incidence plane  131   a,  and the LED array board  30  is fixed to the attachment part  131   c  of the light guide  131 . Then, the relative position of each LED  32  and the light guide  131  on the LED array board  30  may be determined appropriately. Particularly, if the positioning accuracy of LED  32  on the LED array board  30  is high, the accuracy of the relative position between the LED  32  and the light guide  131  becomes high. Thus, positioning becomes easy because the edge side of the LED array board  30  is touched to the incidence plane  131   a.    
         [0048]      FIG. 6C  is a perspective illustration of an optical irradiation unit  218  of another exemplary embodiment of the present invention. In the optical irradiation unit  218  of this embodiment, the direction of light from an exit plane  231   b  of a light guide  231  is almost vertical to the substrate side of the LED array board  30 . The light guide  231  is made in one piece and includes an attachment part  231   c  and a pinched part  231   d.  There is a certain gap between the surface of the attachment part  231   c  and an incidence plane  231   a.  The LED array board  30  is attached on the attachment part  231   c  by using, for example, adhesives, double-stick tape, etc.  
         [0049]     In the embodiment, each LED  232  has the exit plane which is in parallel with the substrate side of the LED array board  30 . The edge side of the LED array board  30  is touched to the pinched part  231   d,  and the LED array board  30  is fixed to the attachment part  231   c  of the light guide  231 . Then, the exit plane of the LED  232  may face the incidence plane  231   a,  and the incidence plane  231   a  may be near to or touching the exit plane of the LED  232 . Thus, the relative position of each LED  232  and the light guide  231  on the LED array board  30  may be determined appropriately. Particularly, if the positioning accuracy of LED  232  on the LED array board  30  is high, the accuracy of the relative position between the LED  232  and the light guide  231  becomes high. Thus, the positioning becomes easy because the edge side of the LED array board  30  is touched to the pinched part  231   d.    
         [0050]     According to this embodiment, the light from the LED  232  enters the incidence plane  231   a.  Then, the light exits from the exit plane  231   b  of the light guide  231 . The output light has almost a vertical direction (i.e., perpendicular) with respect to the substrate side of the LED array board  30 .  
         [0051]      FIG. 6D  is a perspective illustration of an optical irradiation unit  318  of another exemplary embodiment of the present invention. A light guide  331  has plural projection parts  331   e  perpendicularly projected from an incidence plane  331   a.  There is a space for each LED  32  to fit in between the projection parts  331   e.  When attaching the light guide to the LED array board  30 , the relative position of each LED  32  and the light guide  331  on the LED array board  30  may be positioned easily and correctly by fitting the LED  32  between the projection parts  331   e.  Although the fit space is provided corresponding to the LED  32 , at least one fit space is enough for the LED  32  fitting.  
         [0052]      FIG. 7A  is an illustration showing a light path of the light incident on the connecting plane  31   c  of the light guide  31 .  FIG. 7B  is an illustration showing the light path of the light passing through a light guide  431 , which is constituted so that the connecting plane  431   c  of the light guide  431  may become vertical to the incidence plane  431   a.  The light guide  431  in  FIG. 7B  is the same as the light guide  431  in  FIG. 2 . As shown in  FIG. 7B , the incidence light which has an angle θ 2  to an incidence plane  431   a  of the light guide  431  reaches a connecting plane  431   c  with an incidence angle θ 2  to the connecting plane  431   c.  Since the incidence angle θ 2  is smaller than a critical angle α to the connecting plane  431   c,  the light incident to the connecting plane  431   c  is refracted by the connecting plane  431   c,  and penetrates the connecting plane  431   c.  Consequently, the light incident on the connecting plane  431   c  exits to the outside of the light guide  431 .  
         [0053]     On the other hand, in the light guide  31  of this embodiment, the light incident on the connecting plane  31   c,  which has an angle θ 2  to the incidence plane  31   a  of the light guide  31  as shown in  FIG. 7A , reaches the connecting plane  31   c  with an incidence angle θ 1  to the normal line N of plane  31   c.  In this embodiment, since the plane  31   c  inclines at an angle β to the normal line N of the incidence plane  31   a,  the incidence angle θ 1  is larger than the incidence angle θ 2  in the light guide  31  shown in  FIG. 7A . In more detail, the incidence angle θ 1  is larger than the critical angle α to the side  31   c.  Then, the incidence light which reaches the side  31   c  is totally reflected by the plane  31   c.  Consequently, this incidence light pass through the inside of the light guide without exiting to the outside of the light guide  31 , finally reaches the exit plane  31   b  of the light guide  31 , and exits from the exit plane  31   b  to the outside of the light guide.  
         [0054]     According to this exemplary embodiment, the light guide  31  leads much more light to the exit plane  31   b  than that of the light guide  431 . As a result, the optical irradiation equipment using the light guide  31  irradiates with more intense light to the target domain of the manuscript as the portion of the width X on the manuscript shown in  FIG. 1A  than that of the optical irradiation equipment using the light guide  431 .  
         [0055]     As shown in  FIG. 7B , in a case that the connecting plane  431   c  is vertical to the incidence plane  431   a  and the light guide is made by generally used resin, the incidence light which penetrates through the connecting plane  431   c  is the light which is irradiated from the LED  32  having the larger angle than a half-value angle (explained below) of the light irradiated from the LED  32  and that enters the incidence plane  431   a.    
         [0056]     An explanation of half-value angle follows.  FIG. 8  is an illustration showing light distribution of light exiting the LED  32 . This light distribution shows the light level of the every point which is in equal distance from the central point of the exit plane of the LED  32 . The light level is the relative value compared to the point located on the normal line from the central point as  100 . In addition, the LED  32  is driven to generate the maximum light level at the point located on the normal line. If the LED  32  has the ideal light distribution, the shape of the distribution becomes a perfect circle, but the LED  32  of this embodiment forms an ellipse as shown in  FIG. 8 . The line which connects the central point and a point of the 50 level and the normal line make an angle γ 0 . The γ 0  is called the half-value angle. As shown in  FIG. 8 , the half-value angle γ 0  of the light irradiated from the LED  32  in this embodiment is about 51 degrees.  
         [0057]     In this embodiment, the connecting plane  31   d  of the light guide is vertical to the incidence plane  31   a.  Therefore, in the connecting plane  31   d,  the incidence light may not be led to the exit plane  31   b,  because the incidence light pass through the connecting plane  31   d  like in the light guide  431  as shown in  FIG. 7B . In order to lead the incidence light to the exit plane  31   b,  aluminum may be evaporated to the substrate side of the LED array board  30  where the connecting plane  31   d  is fixed so that the substrate side may be reflective surface. In this case, the light which exits from the connecting plane  31   d  to the outside of the light guide is reflected in the substrate, and it may enter the light guide again through the connecting plane  31   d.  Then, if this light reaches the connecting plane  31   c,  it may totally reflect in the connecting plane  31   c,  and the light may be led to the exit plane  31   b  finally.  
         [0058]     Next, configuration of the optical irradiation unit of another exemplary embodiment is explained.  FIG. 9  is an illustration showing a general configuration of the optical irradiation unit  918  of the embodiment. A light guide  931  has an incidence plane  931   a,  an exit plane  931   b,  a connecting plane  931   c,  a connecting plane  931   d,  etc. The connecting planes  931   c  and  931   d  incline at the angle β to the normal line N of the incidence plane  931   a.  Therefore, the cutting plane which cut the light guide  931  along the direction of the normal line of the incidence plane  931   a  so that it may pass through these two connecting planes  931   c  and  931   d  has a shape of trapezoid. The incidence plane  931   a  corresponds to the short side of the trapezoid and the exit plane  931   b  corresponds to the long side of the trapezoid.  
         [0059]     In this embodiment as shown in  FIG. 9 , the LED  32  and the light guide  931  are so arranged that the direction of the light outputting from the exit plane  931   b  is about parallel with the side of the LED array board  30 . However, in this embodiment, the two above-mentioned connecting planes  931   c  and  931   d  are plane symmetry to the specific plane (it is a parallel plane to the direction of a sequence of LED  32 ) which is along the direction of a normal line of the incidence plane  931   a.  Therefore, in the direction in which the connecting planes  931   c  and  931   d  face each other (horizontal direction in  FIG. 9 ), the LED  32  and the light guide  931  are arranged so that the center of the exit side  32   b  of the LED  32  may be matched with the center of the incidence plane  931   a  of the light guide  931 . Then, in the direction in which the connecting planes  931   c  and  931   d  face each other (horizontal direction in  FIG. 9 ), the partial intensity of the exit light from the exit plane  931   b  of the light guide  931  may be prevented. The more intensive light is irradiated to the target domain of the manuscript as the portion of the width X on the manuscript shown in  FIG. 1A  than that of the optical irradiation equipment without the use of the plane symmetry.  
         [0060]     Next, a configuration of an optical irradiation unit of another exemplary embodiment is explained.  FIG. 10  is an illustration showing a general configuration of the optical irradiation unit  1018  of the embodiment. A light guide  1031  has an incidence plane  1031   a,  an exit plane  1031   b,  a connecting plane  1031   c,  a connecting plane  1031   d,  a connecting plane  1031   e,  a connecting plane  1031   f,  etc. The connecting planes  1031   c  and  1031   d  incline at the angle β′ to the normal line N of the incidence plane  1031   a.  The connecting planes  1031   e  and  1031   f  are in parallel with the normal line N.  
         [0061]     The incidence angle to the connecting plane  431   c  of the incidence light from the incidence plane  431   a  becomes large as the distance from the incidence plane  431   a  becomes large. Therefore, even if the connecting plane  431   c  is in parallel with the direction of the normal line of the incidence plane  431   a  as the light guide  431  shown in  FIG. 7B , at the point on the connecting plane  431   c  which is a predetermined distance from the incidence plane  431   a,  the incidence light may not penetrate the point on the connecting plane  431   c.  That is, only a part of the connecting plane  431   c  near the incidence plane  431   a  a problem in which the incidence light exit to the outside of the light guide  431  shown in  FIG. 7B . Then, in this embodiment, only the portion where this problem occurs is made to be inclined by angle β′ to the normal line N of the incidence plane  1031   a,  and it corresponds to the connecting planes  1031   c  and  1031   d.    
         [0062]     In this embodiment, the boundary between the connecting planes  1031   c  and  1031   e,  and the boundary between the connecting planes  1031   d  and  1031   f  may be determined as follows. In a case that the incidence light from the incidence plane  1031   a  to a plane including the connecting plane  1031   d  or  1031   f  make an incidence angle to the plane, if the angle becomes a critical at the point on the plane, the boundary is determined on this point.  
         [0063]     The light guide  1031  has no dent place on the connecting planes between the planes  1031   a  and  1031   b.  Therefore, in manufacturing the light guide  1031  using a metallic mold, the resin in the metallic mold can be easily taken out from the metallic mold by taking out from the exit plane  1031   b  side of the light guide  1031 .  
         [0064]     The incidence light which reaches the connecting planes  1031   c,    1031   d,    1031   e,  and  1031   f  is totally reflected by the connecting planes. Consequently, this incidence light passes through the inside of the light guide without exiting to the outside of the light guide  1031 , finally reaches to the exit plane  1031   b  of the light guide  1031 , and exits from the exit plane  1031   b  to the outside of the light guide. According to the embodiment, the light guide  1031  leads much more light to the exit plane  1031   b  than that of the light guide  431 . As a result, the optical irradiation equipment using the light guide  1031  irradiates with more intensive light to the target domain of the manuscript as the portion of the width X on the manuscript shown in  FIG. 1A  than that of the optical irradiation equipment using the light guide  431 . In addition, in the optical irradiation equipment of the embodiment, plural LEDs  32  and light guide are arranged so that all light from the LEDs  32  may enter the incidence plane of the light guide. In a case where the plural LEDs  32  are used as a light source, it is desirable for all light from the LEDs  32  to enter the light guide, because it is difficult to intensify the light of the LEDs. In this way, it is possible to use the light irradiated from the plural LEDs  32  without wasting. If the optical intensity of the LED  32  is large enough, a part of the light from the plural LEDs  32  may not enter the incidence plane of the light guide.  
         [0065]     Furthermore, in the optical irradiation equipment of the embodiment, a light source may be realized with small power consumption and calorific value, because the plural LEDs  32  are used as a light source. The cost of scanner is low by using the optical irradiation equipment of the embodiment. The cost of the full color copying machine  1 , which is an image forming apparatus, is also low by using the scanner.  
         [0066]     Furthermore, the copying machine has been mentioned as the embodiment of the invention. However, this invention may also apply to an image reading device, such as a scanner, a facsimile, etc., having the same configuration as the image reading part of the copying machine.  
         [0067]     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.  
         [0068]     This patent specification is based on Japanese patent applications, No. JPAP2005-173453 and JPAP2005-173445 both filed on Jun. 14, 2005 in the Japan Patent Office, the entire contents of each of which are incorporated by reference herein.