Abstract:
In an image formation apparatus, a light emitted from a light source is deflected towards a condensing lens, the condensing lens condenses the light and focuses the light on an image carrier. An optical housing houses the condensing lens. The condensing lens is fixed to a fixing member and the fixing member is fixed to the optical housing. The condensing lens may be fixed to the fixing member with adhesive. The fixing member may be fixed to the optical housing with adhesive, screws, or snap fastners.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1) Field of the Invention  
           [0002]    The present invention relates to an image formation apparatus in which a condensing lens of a writing unit is fixed to an optical housing.  
           [0003]    2) Description of the Related Art  
           [0004]    [0004]FIG. 8 is a cross-section of a configuration of a conventional copying machine, FIG. 9 is a cross-section of a scanner (i.e., image reading apparatus) of the copying machine, and FIG. 10 is a perspective view of a writing unit (i.e., laser beam scanner) of the copying machine.  
           [0005]    The copying machine has a scanner  11 , a printer  12 , and a document feeder  13 . The printer includes a writing unit  70 A. The document feeder  13  automatically conveys one sheet of document set on this document feeder onto a contact glass  14 . Moreover, the document feeder  13  discharges the document from the contact glass  14  to the outside once the copying is over.  
           [0006]    The scanner  11  has a first carriage A, and a second carriage B, as shown in FIG. 9. A light source including an illumination lamp  15  and a reflection mirror  16 , and a first mirror  17  are provided on the first carriage A. A second mirror  18  and a third mirror  19  are provided on the second carriage B.  
           [0007]    The document is scanned as follows. The first carriage A moves forward at a constant speed, and the second carriage B moves forward at a speed of one half of that of the first carriage A. The illumination lamp  15  and the reflection mirror  16  illuminate the document. A lens  21  forms an image on a charge-coupled device (hereinafter, “CCD”) sensor  22  via the first mirror  17 , the second mirror  18 , the third mirror  19 , and a color filter  20 . The CCD sensor  22  converts the optical image of the document into analog electric signals, and outputs the analog image signal. Finally, the first carriage A and the second carriage B return to their home positions respectively.  
           [0008]    An analog-to-digital converter converts the analog image signal from the CCD sensor  22  into a digital image signal. An image processing unit  23  carries out various kinds of image processing, such as a binarization, a multiple value processing, multiplication, edition. If a three-line CCD having a line of CCD each for a red (R) filter, a green (G) filter, and a blue (B) filter is provided, then a color document can be read.  
           [0009]    In the printer  12 , a driving section (not shown) rotates a photosensitive drum (i.e., image carrier)  25  during the copying operation. A charging unit  26  uniformly charges the photosensitive drum  25 . The digital image signal processed by the image processing unit  23  is sent to a driving unit not shown. The writing unit  70 A exposes the image according to the digital image signal, and forms an electrostatic latent image on the photosensitive drum  25 . A developing unit  28  develops the electrostatic latent image on the photosensitive drum  25 , into a toner image.  
           [0010]    One paper feeding unit selected from among paper feeding units  33  to  35  feeds a transcription paper (not shown) to a resist roller  36 . The transcription paper is sent from the resist roller  36  in timing with the image on the photosensitive drum  25 . A transfer apparatus  30  transfers the toner image formed on the photosensitive drum  25 , onto the transcription paper. A separating unit  31  separates the transcription paper from the photosensitive drum  25 , and conveys the transcription paper, and a conveying unit  37  conveys this transcription paper. A fixing unit  38  fixes the transferred image, and discharges the fixed image to a tray  39 . A cleaning unit  32  cleans the photosensitive drum  25  after the transcription paper is separated, and removes residual toner.  
           [0011]    As shown in FIG. 10, in the writing unit  70 A, a collimating lens (not shown) transforms a laser beam emitted from a semiconductor laser into a parallel light flux. This parallel light is passed through an aperture (not shown) of specific shape to shape the light flux into a certain shape. A cylindrical lens  40   a  focuses this light flux into a sub-scanning direction, and makes the light flux fall onto a polygon mirror  42 . The polygon mirror  42  has an accurate polygon. A polygon motor  41  rotates the polygon mirror  42  in one direction at a constant speed. The rotation speed of the polygon mirror  42  is determined in accordance with the rotation speed of the photosensitive drum  25 , the writing density of the writing unit  70 A, and the number of planes of the polygon mirror  42 .  
           [0012]    The polygon mirror  42  deflects the light flux so that the light flux falls on an fθ lens  43 . The fθ lens  43  transforms the laser beam into a shape such that a scanning light of a steady angular speed from the polygon mirror  42  scans the photosensitive drum  25  at an equal speed. The laser beam from the fθ lens  43  forms an image on the photosensitive drum  25  via a reflection mirror  45  and a dust-proof glass  46 . The fθ lens  43  also has an optical face tangle error correction function. A synchronization detection mirror  47  reflects the laser beam that passes through the fθ lens  43 , at the outside of the image area, and leads the laser beam to a synchronization detection sensor  48 . The synchronization detection sensor  48  outputs a detection result, thereby to obtain a synchronization signal that becomes a reference of a head of a main scanning direction.  
           [0013]    A suction fan  24  is disposed at a lower portion of one end of the scanner  11 . A blower  90  is disposed near the developing unit  28  within the printer  12 . External air suctioned with the suction fan  24  via an external cover flows toward the image processing unit  23  within the scanner  11 , and it is discharged to the outside of the copying machine. This air cools the optical system (i.e., optical parts) within the scanner  11 . The external air suctioned with the blower  90  via the external cover cools around the photosensitive drum  25 , and thereafter cools the polygon motor  42  and the optical system within the writing unit  70 A.  
           [0014]    Various configurations have been proposed to fix the condensing lens (hereinafter, “lens”) of the scanning and image formation optical system, in other words, the scanning lens, to an optical housing. For example, when the lens is positioned or fixed in a corresponding portion of the lens within the image area, this lens is fitted to the optical housing via an adhesive layer, when the lens is directly brought into contact with the housing.  
           [0015]    Although the optical housing is substantially airtight, the temperature inside the optical housing or of the optical housing changes depending on, for example, the duration for which the image formation apparatus is used, or even due to a change in the environmental temperature.  
           [0016]    If the temperature inside or of the optical housing changes, the lens, because it is fitted to the optical housing directly or via an adhesive, deforms. Since the fθ lens is long and made of plastic, it deforms considerably. If the lens deforms, its optical characteristics change. If the optical characteristics of the lens change, the image quality in a sub-scanning direction degrades. This problem becomes particularly prominent if the condensing lens is made by molding or the optical housing is made of a material having low specific heat.  
         SUMMARY OF THE INVENTION  
         [0017]    It is an object of the present invention to solve at least the problems in the conventional technology.  
           [0018]    In an image formation apparatus according to the present invention, a light emitted from a light source is deflected towards a condensing lens, the condensing lens condenses the light and focuses the light on an image carrier. An optical housing houses the condensing lens. The condensing lens is fixed to a fixing member and the fixing member is fixed to the optical housing. The condensing lens may be fixed to the fixing member with adhesive. The fixing member may be fixed to the optical housing with adhesive, screws, or snap fastners.  
           [0019]    The other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a top plan view of a configuration for fixing a condensing lens in an optical housing according to a first embodiment of the present invention;  
         [0021]    [0021]FIG. 2 is a cross-section of the configuration shown in FIG. 1;  
         [0022]    [0022]FIG. 3 is a top plan view of a configuration for fixing a condensing lens in an optical housing according to a second embodiment of the present invention;  
         [0023]    [0023]FIG. 4 is a cross-section of the configuration in FIG. 3 cut along a line A-A;  
         [0024]    [0024]FIG. 5 is a cross-section of a configuration for fixing a condensing lens in an optical housing according to a third embodiment of the present invention;  
         [0025]    [0025]FIG. 6 is a top plan view of a configuration for fixing a condensing lens in an optical housing according to a fourth embodiment of the present invention;  
         [0026]    [0026]FIG. 7 is a cross-section of the configuration shown in FIG. 6;  
         [0027]    [0027]FIG. 8 is a cross-section of a configuration of a conventional copying machine;  
         [0028]    [0028]FIG. 9 is a cross-section of a scanner of the conventional copying machine; and  
         [0029]    [0029]FIG. 10 is a perspective view of a writing unit of the conventional copying machine. 
     
    
     DETAILED DESCRIPTION  
       [0030]    Exemplary embodiments of the configuration for fixing a lens according to the present invention will be explained with reference to the accompanying drawings.  
         [0031]    [0031]FIG. 1 is a top plan view of a configuration for fixing a condensing lens (i.e., scanning lens) according to a first embodiment of the present invention. FIG. 2 is a cross-section of the configuration shown in FIG. 1. Elongated bosses  105   a ,  105   b , and  105   c  project from a surface of an optical housing  102 . The bosses  105   a ,  105   b , and  105   c  are provided at positions that are outside of an image formation area F of the condensing lens  101 . A fixing member  103  is fixed, to the surface of the optical housing  102 , between the condensing lens and the optical housing  102 , with an adhesive  114 . The condensing lens  101  is fixed, to the surface of the fixing member  103 , with an adhesive  104 . The adhesives  104  and  114  may be an ultraviolet cure adhesive or a two-sided tape. A surface, of the condensing lens  101 , that is perpendicular to the length direction of the condensing lens  101 , is made to abut against the boss  105   a . A surface, of the condensing lens  101 , that is parallel to the length direction of the condensing lens  101 , is made to abut against the bosses  105   b  and  105   c . As a result, the condensing lens  101  is secured firmly. In other words, the boss  105   c  restricts the movement of the condensing lens  101  in the length direction, and the bosses  105   a  and  105   b  restrict the movement of the condensing lens  101  in the direction (hereinafter, “width direction”) that is parallel to the length direction.  
         [0032]    It may be noticed that, the other end or surface in the length direction, and the other end or surface in width direction, of the condensing lens  101  are free. When the condensing lens  101  deforms due to changes in the environmental temperature, the condensing lens  101  expands or contracts in the direction in which it is free, and the position of the condensing lens  101  does not change. As a result, even if the condensing lens  101  or the fixing member  103  made by molding acrylic resin or polycarbonate resin is used, the image quality does not degrade. Moreover, even the optical housing  102  may be made of an aluminum die-cast product, which has low specific heat.  
         [0033]    According to the first embodiment, the condensing lens  101  is fixed to the optical housing via the adhesives  104 ,  114 , and the fixing member  103 . The fixing member  103  is made of material having low heat conductivity. Therefore, the fixing member  103  does not conduct heat to the condensing lens  101  from the optical housing  102 . Therefore, the image quality does not degrade even if the temperature inside or of the optical housing  102  changes.  
         [0034]    [0034]FIG. 3 is a top plan view of a configuration for fixing a condensing lens according to a second embodiment of the present invention. FIG. 4 is a cross-section of the configuration along a line A-A. The fixing member  103  is rectangular. The length L of the fixing member  103  is more than the width W in the widest portion of the condensing lens  101 . This fixing member  103  is provided below the widest portion of the condensing lens  101  to be parallel to the width direction of the condensing lens  101 .  
         [0035]    On the lower surface of the lens  101 , a first projection  111  is provided to position the long side of the lens, and a second projection  112  is provided to position the short side of the lens respectively. A positioning projection (i.e., positioning pin)  110  and a first reference groove  108  are provided on the upper surface of the housing  102  respectively. A through-hole (i.e., long hole)  107  is formed in the fixing member  103  along its longitudinal direction. A second reference groove  109  is formed on the upper surface of the fixing member  103  along its width direction. A projection  106  is provided on the lower surface of the fixing member  103 .  
         [0036]    An ultraviolet cure adhesive  104  is coated onto a predetermined portion of the upper surface of the fixing member  103 . The first projection  111  provided on the lens  101  is brought into contact with an upper portion of a side surface of the long hole  107  of the fixing member  103 . The second projection  112  is brought into contact with the second reference groove  109  of the fixing member  103 . With this arrangement, the lens  101  is positioned on the fixing member  103 . Ultraviolet rays are irradiated onto the fixing member  103  from above the lens  101 , thereby to fix the lens  101  to the fixing member  103  with the adhesive  104 . The projection  106  of the fixing member  103  is inserted into the first reference groove  108  of the housing  102 , and is brought into contact with the side surface of this groove. The lower portion of the side surface of the long hole  107  of the fixing member  103  is brought into contact with the positioning projection  110  of the housing  102 . With this arrangement, the fixing member  103  is positioned on the housing  102 . The fixing member  103  is fixed to the housing  102  with screws  113   a  and  113   b . The first projection  111  is a member to position the long side of the lens  101 , and the second projection  112  is a member to position the short side of the lens  101 . The projection  106  is a member to position the long side of the fixing member  103 , and the positioning projection  110  is a member to position the short side of the fixing member  103 . The projections  106  and  112  extend to the longitudinal direction.  
         [0037]    According to the second embodiment, the condensing lens  101 , the fixing member  103 , and the housing  102  can be mutually positioned easily and at high precision. The fixing member  103  is made of material having low heat conductivity. Thus, since the fixing member  103  does not conduct heat to the condensing lens  101  from the optical housing  102 , the image quality does not degrade even if the temperature inside or of the optical housing  102  changes.  
         [0038]    Moreover, in the conventional configuration, the fixing member is directly fixed to the optical housing with an adhesive, which makes mounting and dismounting of the fixing member cumbersome. On the other hand, in the second embodiment, the fixing member  103  is fixed to the optical housing  102  with the screws. As a result, the fixing member  103  can be easily mounted to and dismounted from the optical housing  102  by tightening or loosing the screws. The fixing member  103  and the optical housing can be even be recycled.  
         [0039]    [0039]FIG. 5 is a cross-section of a configuration for fixing a condensing lens according to a third embodiment of the present invention. FIG. 5 illustrates a same view as FIG. 4. In the configuration shown in FIG. 4, the fixing member  103  is fixed to the optical housing  102  with the screws  113   a  and  113   b . On the other hand, in the configuration shown in FIG. 5, the fixing member  103  has engagement members, that is, snap fasteners  115   a  and  115   b , formed integrally as a plastic member. This fixing member  103  is snapped to the optical housing  102  with the snap fasteners. Rest of the configuration is similar to that shown in FIG. 4.  
         [0040]    Specifically, on the lower surface of the lens  101 , the first projection  111  is provided to position the long side of the lens, and the second projection  112  is provided to position the short side of the lens respectively. The positioning projection (i.e., positioning pin)  110  and the first reference groove  108  are provided on the upper surface of the housing  102  respectively. Through-holes  116   a  and  116   b  are formed in the housing  102  to pass from the upper surface to the lower surface of the housing  102 . The long hole  107  is formed in the fixing member  103  to pass from the upper surface to the lower surface of the fixing member  103 , along the longitudinal direction of the fixing member  103 . The second reference groove  109  is formed on the upper surface of the fixing member  103 . The projection  106  is provided on the lower surface of the fixing member  103 . Snap fasteners  115   a  and  115   b  are provided at both ends of the short side of the fixing member  103 , to extend downward from the lower surface of the fixing member  103 .  
         [0041]    The ultraviolet cure adhesive  104  is coated onto a predetermined portion of the upper surface of the fixing member  103 . The first projection  111  provided on the lens  101  is brought into contact with the side surface of the long hole  107 . The second projection  112  is brought into contact with the side surface of the second reference groove  109 . With this arrangement, the lens  101  is positioned on the fixing member  103 , thereby to fix the lens  101  to the fixing member  103  with the adhesive  104 . The projection  106  of the fixing member  103  is inserted into the first reference groove  108 , and is brought into contact with the side surface of this groove. The side surface of the long hole  107  of the fixing member  103  is brought into contact with the positioning projection  110  of the housing  102 . The snap fasteners  115   a  and  115   b  are pushed into the through-holes  116   a  and  116   b , thereby to snap the fixing member  103  to the housing  102 . The first projection  111  is a member to position the long side of the lens  101 , and the second projection  112  is a member to position the short side of the lens  101 . The projection  106  is a member to position the long side of the fixing member  103 , and the positioning projection  110  is a member to position the short side of the fixing member  103 . The projections  106  and  112  extend to the longitudinal direction.  
         [0042]    According to the third embodiment, the condensing lens  101 , the fixing member  103 , and the housing  102  can be mutually positioned easily and at high precision. The fixing member  103  is made of material having low heat conductivity. Thus, since the fixing member  103  does not conduct heat to the condensing lens  101  from the optical housing  102 , the image quality does not degrade even if the temperature inside or of the optical housing  102  changes.  
         [0043]    Moreover, in the conventional configuration, the fixing member is directly fixed to the optical housing with an adhesive, which makes mounting and dismounting of the fixing member cumbersome. On the other hand, in the second embodiment, the fixing member  103  is fixed to the optical housing  102  with the snap fasteners. Therefore, the lens having the fixing member  103  can be easily mounted to and dismounted from the housing  102 . As a result, the fixing member  103  can be easily mounted to and dismounted from the optical housing  102 . The fixing member  103  and the optical housing can be even be recycled. Moreover, since the screws are not required, the number of parts, in other words, the cost is reduced.  
         [0044]    [0044]FIG. 6 is a top plan view of a configuration for fixing a condensing lens according to a fourth embodiment of the present invention. FIG. 7 is a cross-section of the configuration shown in FIG. 6. A glass molded product or a plastic molded product having an ultraviolet ray transmittance equal to or more than 50 percent is used for the fixing member  103 . Ultraviolet cure adhesives  117   a  and  117   b  are coated onto the upper and lower sides of the fixing member  103 , and the fixing member  103  is mounted on a predetermined portion of the bottom surface of the housing  102 . The lens  101  is mounted on the fixing member  103 , and is positioned there with the bosses  105   a  to  105   c  in a similar manner to that according to the first embodiment.  
         [0045]    Ultraviolet rays are irradiated to the ultraviolet cure adhesives  117   a  and  117   b  from above the lens to cure these adhesives. Accordingly, both the lens  101  and the fixing member  103  are fixed to the housing  102  at the same time. The fixing member  103  having the ultraviolet ray transmittance equal to or more that 50 percent is used in the present embodiment. This is for the purpose of making the ultraviolet rays having transmitted through the lens  101  and the adhesive  117   a  transmit through the fixing member  103  at this high transmittance, thereby to cure the adhesive  117   a  and  117   b  at the same time.  
         [0046]    In the configuration of the first embodiment shown in FIG. 2, it is also preferable that the fixing member  103  having the ultraviolet ray transmittance equal to or more that 50 percent is also used to fix the fixing member  103  to the housing  102  with the ultraviolet cure adhesive  114 . Specifically, the ultraviolet cure adhesives  104  and  114  are coated onto the upper and lower surfaces of the glass molded fixing member, and this fixing member is mounted on the bottom surface of the housing  102 . The condensing lens  101  is mounted on the fixing member  103 . One end of the long side of the lens is brought into contact with the boss  105   c , and one end of the short side (i.e. width) is brought into contact with the bosses  105   a  and  105   b  respectively, thereby to position the lens. Thereafter, ultraviolet rays are irradiated onto the fixing member from above the lens, thereby to fix the lens to the fixing member and fix the fixing member to the housing at the same time.  
         [0047]    Thus, according to the configuration for fixing the condensing lens of the present invention, the fixing member is made of material having low heat conductivity so that it does not conduct heat to the condensing lens from the optical housing. As a result, since the condensing lens does not deform much, the image quality does not degrade even if the temperature inside or of the optical housing changes.  
         [0048]    The fixing member may be fixed to the optical housing by an adhesive, screws, or the snap fasteners. When the fixing member is fixed by screws or snap fasteners, the fixing member can be mounting on or dismounting from the optical housing easily.  
         [0049]    The present document incorporates by reference the entire contents of Japanese priority document, 2002-239381 filed in Japan on Aug. 20, 2002.  
         [0050]    Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.