Abstract:
An image forming apparatus includes a photoconductor, a light source that emits a light beam, and a scanning device that guides a light beam emitted from the light source onto a surface of the photoconductor so as to scan the surface of the photoconductor with the light beam to form a latent image thereupon. A housing, to which the light source and the scanning device are mounted, is mounted to a main body of the apparatus by a stay. The housing is supported by the stay such that an angle of a scanning direction of the light beam relative to a direction in which a surface of the photoconductor moves is adjustable so as to be at a substantially right angle and thereby an image is formed in a rectangular form by way of rotating the housing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus having an image writing device for writing a latent image on a surface of a photoconductor by deflecting a light beam by way of an optical defector and exposing the surface of the photoconductor with the deflected light beam, and more particularly to an image forming apparatus in which adjustment of a scanning direction of the light beam so as to be at a right angle relative to a direction in which a surface of the photoconductor moves such that a rectangular latent image is easily formed. 
     2. Discussion of the Background 
     It is well known that digital copying machines using electrophotography include an image writing device for writing a latent image on a surface of a photoconductor by deflecting a light beam by way of an optical defector and exposing the surface of the photoconductor with the deflected light beam. 
     FIG. 1 illustrates an example of such a digital copying machine. In FIG. 1, digital copying machine  100  includes an image reading device  111 , a printing device  112  and an automatic document feeding device  113 . The automatic document feeding device  113  separates each of the original document sheets set in the automatic document feeding device  113  and feeds the separated sheets to a contact glass  114  into a reading position. After an image of the original document is read, the automatic document feeding device  113  discharges the sheet from the reading position on contact glass  114 . 
     FIG. 2 is a sectional drawing illustrating image reading device  111 . Image reading device  111  includes a first carriage A having a light source including an illuminating lamp  115 , a reflecting mirror  116 , and a first mirror  117  (shown in FIG.  1 ). A second carriage B of image reading device  111  includes a second mirror  118  and a third mirror  119 . When reading an original document placed on contact glass  114 , first carriage A travels at a constant speed while second carriage B travels at a speed half that of first carriage A, thereby optically scanning the original document on the contact glass  114 . The original document on contact glass  114  is illuminated by illuminating lamp  115  and reflecting mirror  116 . As shown in FIG. 1, the light reflected by the original document is directed to a charge-coupled device (CCD)  122  by a lens  121  via first mirror  117 , second mirror  118 , third mirror  119 , and a color filter  120 . CCD  122  converts the received light image to electrical signals and outputs analog image signals representing the image of the original document. Referring again to FIG. 2, after the image of the original document is read, first carriage A and second carriage B return to respective home positions (represented by the solid line depictions) from the positions where image reading ends (represented by the line-and-dot line depictions). CCD  122  may be configured such that three arrays of CCD elements are arranged for R (red), G (green) and B (blue), respectively, for reading a original color document. 
     Referring now to FIG. 1, the analog image signals output from CCD  122  are converted into digital image signals by an analog-to-digital converter (not shown) and various kinds of image processing, such as converting multi-value data into binary data and vice versa, gradation level conversion, magnification ratio change, image editing and so on, are applied to the digital image signals by an image processing circuit included on image processing board  123 . 
     In order to prepare photoconductor drum  125  to receive a latent image, photoconductor drum  125  is driven by a drive unit (not shown) and the surface of the photoconductor drum  125  is uniformly charged by a charging device  126 . After the digital image signals have been processed with image processing board  123 , they are sent to a semiconductor circuit board (not shown), and a latent image is formed on the surface of photoconductor drum  125  according to the digital image signals with an image exposure operation performed by a laser beam scanning device  127 . The latent image on the photoconductor drum  125  is then developed with toner to form a visible toner image by developing device  128 . 
     A transfer sheet is fed to a registration roller  136  from a selected one of sheet cassettes  133 ,  134  and  135 , toward the photoconductor drum  125  at a timing to register the leading edge of the transfer sheet with the leading edge of a toner image formed on the surface of the photoconductor drum  125 . The toner image on photoconductor drum  125  is transferred onto the transfer sheet with transfer device  130 . The transfer sheet carrying the toner image is separated from the photoconductor drum  125  with separating device  131  and is conveyed by conveying device  137  to fixing device  138 , where the toner image is fixed onto the transfer sheet. The transfer sheet carrying the fixed toner image is then discharged onto an exit tray  139 . The surface of the photoconductor drum  125  is cleaned with cleaning device  132  after the transfer paper is separated such that residual toner is removed from the surface of photoconductor drum  125 . 
     FIG. 3 is a schematic drawing illustrating the construction of the laser beam scanning device  127  and the relative positions of scanning device  127  and photoconductor drum  125 . Laser beam scanning device  127  includes a semiconductor laser unit  140  having a semiconductor laser. A laser beam light emitted from the semiconductor laser is converted to a parallel light flux with a collimate lens (not shown) in the semiconductor laser unit  140 . The parallel light flux is then reformed to a predetermined shape by passing through an aperture (not shown) in the semiconductor laser unit  140 . The reformed light flux is converged in the sub scanning direction with cylindrical lens  141  and is thereby directed onto a surface of a polygonal mirror  142 . Polygonal mirror  142  is formed in a polygonal shape and is rotated at a constant speed in a fixed direction with motor  143  (illustrated in FIG.  1 ). The rotation speed of the polygonal mirror  142  is determined according to the rotation speed of the photoconductor drum  125 , the writing resolution of the laser beam scanning device  127 , and the number of surfaces of the polygonal mirror  142 . 
     The laser beam directed onto the polygonal mirror  142  is deflected by a reflecting surface of the polygonal mirror  142  at an equiangular velocity and is thereby directed into an fθ lens  144 . The fθ lens  144  is configured to convert the laser beam deflected by the polygonal mirror  142  at equiangular velocity so as to scan the surface of the photoconductor drum  125  at a constant linear velocity. The laser beam is directed to the surface of the photoconductor drum  125  via reflecting mirror  145  and dust-proof glass  146 . The fθ lens  144  also has a surface tilt correcting function, which causes a portion of the laser beam passing through fθ lens  144  at positions out of the image forming area, to be reflected by a synchronization detection mirror  147  so as to be detected by a synchronization detection sensor  148 . The synchronization detection sensor  148  outputs a detect signal in accordance with the collision of the laser beam thereupon such that a synchronization signal for aligning a writing start position for each scanning in the main scanning direction (indicated by an arrow in FIG. 3) is obtained. 
     Laser beam scanning device  127 , as described above, is attached to a housing of a main body of the digital copying machine  100  such that a latent image is formed on the surface of the photoconductor drum  125  with the laser beam in a rectangular form having a right angle at each comer, i.e., when a rectangular latent image formed on the surface of the photoconductor drum  125  with the laser beam and the latent image is developed with toner, one side of the rectangular toner image is perpendicular to the direction in which the photoconductor drum  125  rotates (parallel to the axis of the photoconductor drum  125 ) and the other side of the rectangular toner image is parallel to the direction in which the photoconductor drum  125  rotates (perpendicular to the axis of the photoconductor drum  125 ), or when the rectangular toner image is transferred onto a transfer sheet, sides of the rectangular toner image are parallel to edges of the transfer sheet respectively or each line extending from an end of a side of the rectangular image is perpendicular to an edge of the transfer sheet. The above feature that an image is formed in a rectangular form is realized if the laser beam of laser beam scanning device  127  scans the surface of photoconductor drum  125  in a direction substantially perpendicular to the direction in which photoconductor drum  125  rotates. Laser beam scanning device  127  is therefore attached to the housing of the main body of the digital copying machine such that the positional relationship between the laser beam scanning device  127  and the photoconductor drum  125  is set and fixed such that the scanning direction of the laser beam is substantially perpendicular to the direction in which the photoconductor drum  125  rotates so that a latent image is formed in a rectangular form. In some image forming apparatuses, relevant parts, such as for example a mirror, are made adjustable, such that, when the apparatus is shipped from the assembling factory, the scanning direction of the laser beam can made perpendicular to the direction in which the photoconductor drum rotates so as to form an image in a rectangular form by way of adjusting the relevant parts. 
     However, even when a laser scanning device is attached to a housing of a main body of an image forming apparatus such that a desired positional relationship between the scanning device and a photoconductor drum for making the scanning direction of the laser beam perpendicular to the rotation direction of the photoconductor (so as to forming an image in a rectangular form) is accomplished as described above, such a positional relationship may be lost during transportation of the apparatus to a user&#39;s cite or due to the condition of the place where the apparatus is placed at the user&#39; site. In particular, when the apparatus is placed on an uneven or inclined plane, thereby distorting the apparatus, the desired positional relationship between the laser beam scanning device and the photoconductor drum may be lost. For example, the surface of the photoconductor drum may be deviated from the position where an image is formed in a rectangular shape with a laser beam of the laser beam scanning device, and thereby, the image is formed, for example, in a parallelogram. 
     Further, because the laser beam scanning device is generally located at the rear side of the apparatus and is packaged in a tightly sealed construction for preventing optical elements which are included in the scanning device being stained with dust, even if optical elements of the scanning device, such as mirrors, are made to be adjustable as above, proper adjustment of such optical elements is not easily accomplished at a user&#39;s site. Furthermore, addition of such adjusting feature increases the cost of the apparatus. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-discussed problems and addresses and resolves the above-described and other problems. Preferred embodiments of the present invention provide an image forming apparatus in which adjustment of a scanning direction of a light beam so as to be substantially perpendicular to a direction in which a surface of a photoconductor moves so that a latent image is formed in a substantially rectangular form is easily performed without increasing the cost of the apparatus. 
     According to a preferred embodiment of the present invention, an image forming apparatus includes a photoconductor, a light source that emits a light beam, and a scanning device that guides a light beam emitted from the light source onto a surface of the photoconductor so as to scan the surface of the photoconductor with the light beam to form a latent image thereupon. A housing, to which the light source and the scanning device are mounted, is supported by a stay and the housing is mounted to a main body of the apparatus via the stay. 
     According to the invention, the housing is supported by the stay such that an angle of a scanning direction of the light beam relative to a direction in which a surface of the photoconductor moves, is adjustable so that the scanning direction can be arranged at a substantially right angle relative to the direction of rotation of the housing. A pair of the stays may be arranged in substantially parallel to a widthwise direction of the photoconductor. A positioning pin may also be provided to the housing, and a positioning pin insertion hole, through which the positioning pin is inserted, is provided for one of the pair of the stays, wherein the housing is rotated around the positioning pin. 
     A driver insertion hole is provided to each of the housing and the stay, and the housing is rotated relative to the stay by inserting a tip end of the driver into the driver insertion hole of the housing and the stay and by rotating the driver. 
     Further, a scale for indicating a rotated position of the housing may provided to the stay. 
     A division of the scale may made such that rotation of the housing relative to the stay over one division of the scale corrects a deviation of the angle of the scanning direction of the light beam relative to the direction in which the surface of the photoconductor moves, from a right angle in an amount corresponding to, when an image of longitudinal and widthwise lines, the widthwise line extending from an end point of the longitudinal line at a right angle relative to the longitudinal line over a maximum widthwise length of the image, is formed, in the formed image, the deviation being equal to a distance of 0.5 mm or 1 mm between the connected ends of the longitudinal and widthwise line images and a point of the longitudinal line image or a point of a longitudinal line extending from the connected ends point, where a line extended from the other end point of the widthwise line image in perpendicular to the longitudinal line image crosses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference tot he following detailed description of when considered in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic drawing illustrating an example of a digital copying machine as an image forming apparatus; 
     FIG. 2 is a sectional drawing illustrating an image reading device of the digital copying machine illustrated in FIG. 1; 
     FIG. 3 is a schematic drawing illustrating the construction of a laser beam scanning device and the positional relationship between the laser beam scanning device and a photoconductor drum in the digital copying machine of FIG. 1; 
     FIG. 4 is a plan view illustrating a structure of a housing, to which a laser beam scanning device is mounted, and a stay supporting the housing, according to an embodiment of the present invention; 
     FIG. 5 is a sectional view of the housing and the stay of FIG. 4, illustrating the relationship between the scanning device and the photoconductor drum; 
     FIGS.  6 ( a ) and  6 ( b ) are plan views illustrating the relationship between the housing and the stay, FIG.  6 ( a ) being a plan view of the stay; 
     FIG. 7 is a section view illustrating the relationship between the housing and the stay at line  7 .— 7 . indicated in FIG.  6 ( b ); 
     FIG. 8 is a section view illustrating the relationship between the housing and the stay at the part where a driver is inserted, at line  8 .— 8 . indicated in FIG.  6 ( b ); 
     FIG. 9 is a plan view illustrating a state where the driver is twisted for adjusting the relationship; 
     FIG. 10 is a schematic drawing illustrating an example of a distance between each division of a scale provided on the stay; and 
     FIGS.  11 ( a ) and  11 ( b ) are diagrams explaining that an image is not formed in a rectangular form. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout several views, preferred embodiments of the present invention are now described. 
     As shown in FIGS. 4 and 5, a housing  16  houses therein components of laser beam scanning device  27 , and is tightly sealed for preventing the components from being stained by dust, and the like. A polygonal mirror  1  is arranged at one end portion of the housing  16  and a mirror  5  for deflecting a laser beam in a direction to impinge a surface of the photoconductor drum  21 , is arranged at the other end portion of the housing  16 . A laser unit  14  is arranged in a position to enable a laser beam emitted from the laser unit  14  to impinge onto mirror  5  by being deflected by polygonal mirror  1 . A collimator lens  15  is arranged in a light path between laser unit  14  and the polygonal mirror  1 , and fθ lenses  2  and  3  and surface tilt correcting lens  4  are arranged between the polygonal mirror  1  and the mirror  5 . Lenses  2 ,  3 ,  4  and  15  accomplish fθ characteristics. Arrow a indicates the direction in which polygonal mirror  1  rotates and ends b and c are the widthwise ends of a scanning line  17  of a laser beam. 
     Housing  16  is positioned so as to span over both a right side stay  18  and a left side stay  19 , and is attached to these stays  18  and  19  such that a laser beam reflected by mirror  5  passes through an opening  6  and scans the surface of photoconductor drum  21 . Stays  18  and  19  are attached to a side plate (not shown) of a main body of the image forming apparatus. Photoconductor drum  21  is rotatably supported by the side plate and is driven to be rotated by a rotation drive device (not shown). 
     Three protruding plates  8 ,  9  and  11  are provided to a lower edge of housing  16 , at the side of the mirror  5  and two additional protruding plates  10  and  12  are similarly provided to the lower edge at the side of the polygonal mirror  1 . Each of plates  8 ,  9 ,  11 ,  10 ,  12  are made substantially parallel to the bottom surface of housing  16 . A pin  11   a  is provided to plate  11  at the bottom surface thereof, protruding substantially perpendicularly downward. When the position of housing  16  is adjusted relative to photoconductor drum  21  (described in detail later), housing  16  is rotated with pin  11   a  being the center of rotation, defining housing rotational axis H R . A jig pin passing hole  26  for receiving a jig pin is formed in protrusion plate  12 . An insertion hole  18   a  for receiving pin  11   a  is formed in right side stay  18  and a jig pin insertion hole  23  for receiving the jig pin via hole  26  is provided in left side stay  19 . Jig pin insertion hole  23  is provided for positioning housing  16  in a default position during assembly. Preferably, housing  16  is positioned in such a default position by inserting pin  11   a  into insertion hole  18   a  provided in right side stay  18  and inserting the jig pin into the matched jig pin insertion hole  23  and jig pin passing hole  26 . 
     Washers  8   a ,  9   a  and  10   a  are arranged at the bottom surfaces of plates  8 ,  9  and  10 , respectively, and the accuracy of the vertical positional relationship between the housing  16  and the photoconductor drum  21  is accomplished and is maintained by arranging the bottom surface of the plates  8 ,  9  and  10  on stays  18  and  19  via washers  8   a ,  9   a  and  10 , respectively. After the vertical positional relationship between housing  16  and photoconductor drum  21  is accomplished, potions of stays  18  and  19  supporting plates  8 ,  9  and  10 , respectively, are connected and fixed with screws. 
     Therefore, when adjusting the relative angular position of housing  16  and photoconductor drum  21  such that the scanning direction of the laser beam is made perpendicular to the direction in which the photoconductor drum  21  rotates (so that a rectangular image is formed), housing  16  is rotated around pin  11   a  either in a clockwise or a counter-clock wise direction after loosening the screws for plates  8 ,  9  and  10 . After the desired relative angular position of housing  16  and photoconductor drum  21  is obtained, housing  16  is fixed to stays  18  and  19  again by the screws. In other words, housing  16  rotates about axis H R , such that protrusion rotates in a plane (not shown) which is substantially parallel to the rotational axis P R  of photoconductive drum  21 . Thus, the relative angular position of housing  16  and photoconductor drum  21  can be easily adjusted at a user&#39;s site without increasing the cost of the apparatus. 
     Further, with the provision of a protrusion  28  to housing  16  and a scale  13  to left side stay  19 , the angular position of the housing  16  can be easily measured. In this example, an indicia on scale  13  for indicating the default position is made longer than other indicia of the scale  13 , so that the angular position of the housing from the default position can be easily identified. 
     As viewed in FIGS.  6 ( a ) and  6 ( b ), scale  13  is provided on an upper surface of left side stay  19  and jig pin inserting hole  23  for positioning housing  16  at the default position is formed at the right side of scale  13 . A hole  22  for inserting a driver is formed above jig pin inserting hole  23  (as shown in FIG.  6 ( a )) and a screw inserting hole  24  for inserting a screw to fix housing  16  to left side stay  19  is provided below jig pin inserting hole  23 . An elongated hole  25  for inserting a screw to pass through hole  24 , jig pin passing hole  26  for passing a jig pin, and a groove  27  to insert therein a driver, are provided at a side of housing  16  as illustrated in FIG.  6 ( b ). Protrusion  28  is formed at a position left of jig pin passing hole  26 , as viewed in FIG.  6 ( b ), so as to point towards scale  13 . Right side stay  18  and housing  16  are configured in substantially the same structure as in the previous embodiment. A washer (not shown) is provided at the bottom surface of the elongated hole  25 . 
     Referring now to FIGS.  6 ( a ),  6 ( b ) and  7 , when adjusting the angular position of housing  16  from the default position, a jig pin (not shown) is preferably inserted in jig pin inserting hole  23  and jig pin passing hole  26 , while groove  27  is overlapped with the driver inserting hole  22 , and elongated hole  25  with screw hole  24 . The jig pin is removed in this state and a driver  29  is then inserted through groove  27  into driver inserting hole  22 . Driver  29  is then twisted as illustrated by the arrow in FIG.  8 . If driver  29  is twisted, for example, in a direction indicated by an arrow “h” in FIG. 9, housing  16  is moved relative to left side stay  19  in the direction indicated by arrow g in FIG.  9 . With this twisting movement of driver  29 , referring now to FIGS. 4 and 5, the angle of the scanning line  17  relative to the direction in which the photoconductor drum  21  rotates, or the angle relative to the axial direction (the longitudinal direction) of the photoconductor drum  21 , is adjusted. Because housing  16  rotates around the positioning pin  11   a , the relative position of respective optical components which are mounted in the housing  16  is not changed with this adjustment. Furthermore, the length of the optical path is not changed and is kept the same. Therefore, the positional relationship between housing  16  and photoconductor drum  21  is adjusted so as to form an image in a rectangular form without deteriorating other optical characteristics, such as, for example, the diameter of the optical beam, and thereby without deteriorating the quality of a resulting image. 
     Scale  13  provided on the upper surface of left side stay  19  may be used simply for generally identifying the amount of angular movement of housing  16  relative to left side stay  19 . However, if the image is not formed in a rectangular form after adjusting the positional relationship between housing  16  and photoconductor drum  21 , as describer above, the positional relationship between housing  16  and photoconductor drum  21  has to be repeated. Therefore, if the amount of the deviation of the form of an image from a rectangular shape, which can be corrected by way of rotating housing  16  over one division of scale  13 , is known in advance, the deviation of an image from a rectangular form can be corrected, so that the image is formed in a rectangular form, at one time by simply rotating the housing  16  for a required number of the divisions of the scale  13  and thereby the time for the adjustment can be saved. 
     Referring now to FIGS. 1,  10  and  11 , assuming that the width of an image is L, the amount of a deviation of the form of an image, from a rectangular form, is Δx (FIGS.  11 ( a ) and  11 ( b )), the distance from the rotational axis of plate  11  to scale  13  is 1 (FIG.  1 ), and the width between each division of scale  13  is Δy (FIG.  10 ), the following formula stands; 
     
       
         Δy/1=Δx/L 
       
     
     Here, the amount of the deviation of the form of an image from a rectangular form (Δx) is measured by forming, for example, an image of a widthwise line and a longitudinal line which are connected to each other forming a right angle at the connected point as illustrated in FIG.  11 ( a ). In FIG.  11 ( a ), a widthwise line  202  extends from one end of longitudinal line  201 , perpendicular to longitudinal line  201 , over a maximum width L of the image. When the size of the image is A3, for example, the length of line  202  is set shorter than the width of the A3 size, 297 mm, to 290 mm, for example. The longitudinal line image is formed, for example, close to a left side edge of a transfer sheet in the direction the sheet travels. 
     Assuming that the above image of the longitudinal and widthwise lines is formed deviated from a rectangular form, as illustrated in FIG.  11 ( b ), the amount of the deviation (Δx) of the image from a rectangular form is expressed in terms of the distance between the connected ends point  203  of the longitudinal and widthwise line images  201  and  202  and a point  204  of the longitudinal line image  201  or a point  205  of a longitudinal line  206  extending from the connected ends point  203  of the longitudinal and widthwise line images  201  and  202 , where a perpendicular line  207  from the other end point  208  of the widthwise line image  202  crosses. 
     If the amount of the deviation Δx is, for example, 0.5 mm, the width of the image L is 290 mm and the distance from the rotation center of the protruded plate  11  to the scale is 400 mm, 
     
       
         Δy=Δx×1/L=0.69 mm. 
       
     
     Accordingly, if the distance between each division of scale  13  is made to 0.69 mm, when adjusting the positional relationship between housing  16  and photoconductor drum  21  so as to form an image in a rectangular form, the deviation distance of 0.5 mm from a rectangular form is corrected by way of rotating housing  16  for one division of scale  13 . Therefore, if the deviation from a rectangular form is, for example, 0.5 mm, the deviation can be corrected by simply rotating housing  16  for one division of scale  13  and if the deviation is 1 mm, the deviation can be corrected by rotating housing  13  for two divisions of scale  23 . Thus, the operation of adjusting the positional relationship between housing  16  and photoconductor drum  21  such that an image is formed in a rectangular form is simplified and the time for the adjustment is saved. 
     Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than specifically described herein. 
     This application is based on Japanese patent application No. 10-032836 filed in the Japanese Patent Office on Feb. 16, 1998, the entire contents of which are hereby expressly incorporated by reference.