Abstract:
A writing device to write an image onto a photoconductor, including a print head having plural LEDs, a first supporting member, having a position determining section to determine the position of the print head, and an adjustment screw, and a second supporting member, having a reference shaft which comes into contact with the first supporting member and movably supports the first supporting member while moving to or separating from the photoconductor, and a pressuring member which presses the first supporting member against the reference shaft, wherein the second supporting member is engaged with the first supporting member by the adjustment screw, whereby when the adjustment screw is rotated, the print head is shifted along with the first supporting member, and a first direction joining the position determining section and the adjustment screw makes a right angle with a second direction joining the adjustment screw and the reference shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2007-039123 filed on Feb. 20, 2007 with the Japanese Patent Office, the entire content of which is hereby incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a writing device, and in particular, to a writing device in which the distance between an LED print head and a photoconductor can be easily adjusted. 
   BACKGROUND OF THE INVENTION 
   Generally, among the writing devices which are used for image forming apparatuses exhibiting an electro-photographic process, a writing device is well known in which LED print heads (hereinafter referred, to “LPH”), having an LED array structured of a plurality of LEDs, are used, and which exposes an image onto a photoconductor to form a latent image. In said LPH, a converging-rod-lens array, generally called a “SELFOC lens”, is used to concentrate light rays so that high resolution is obtained. If the distance between the LPH and the photoconductor varies, the image exposed on the photoconductor becomes out-of-focus, and the resolution is reduced. Further, in typical color image forming apparatuses which superpose plural color images, color unevenness usually tends to occur. 
   In the above-described writing device, in order to obtain preferred type of images, positional accuracy within ±0.1 mm is generally essential for the position of the LPH with respect to the focal surface on the drum of the photoconductor. The more the PLH approaches the heat focus, the more the image quality improves. Therefore, the positional adjustment of the LPH requires precise control. 
   However, in the writing devices which has been conventionally used for the image forming apparatuses, such as copy machines and printers in business offices, the accuracy for assembling the LPH onto the photoconductor tends to be controlled only by the manufacturing accuracy of mechanical parts to support the LPH. In such cases, since the focal depth of the LPH is generally ±0.06 mm, the accuracy for manufacturing the member to support the LPH is not enough to realize the above targeted positional accuracy which is within ±0.1 mm. 
   Unexamined Japanese Patent Application Publication No. 58-205171 discloses an electrostatic printer having a print head unit, in which a light emitting section and a SELFOC lens are mated, and having a positional adjustment member which enables precise adjustment of the assembling position of said print head unit onto the electrostatic printer. 
   Further, Unexamined Japanese Patent Application Publication No. 62-242,929 discloses a writing device having a light emitting section on a frame, and the light emitting section is adjustable, being supported by a positional adjustment member. 
   In Unexamined Japanese Patent Application Publication No. 58-205171, when the print head unit is to be assembled onto a mounting member of the electrostatic printer, a positional adjustment screw of the mounting member is rotated so that the bottom face position of a mounting plate of the print head unit can be moved, whereby after the mounting position of the print head unit is adjusted, the print head unit is fastened by a fastening screw. Due to this structure, the distance between the print head unit and the photoconductor is controlled. However, since the positional adjustment screw and the mounting member are not firm contact with each other, they are not stable in relation to each other, that is, the movement of the print head unit becomes unstable, which results in inaccurate positioning of the print head unit. Further, when the above cited screw is fastened, the position of the print head unit in the longitudinal direction, (which is the axial direction of the photoconductor) may shift, which results in unstable repeatability of the adjustment, as well as an out-of-focus of the produced image. 
   In Unexamined Japanese Patent Application Publication No. 62-242929, a supporting member to support an led array head is allowed to come into contact with a cylindrical positional adjustment member, having an eccentric hole, mounted on a frame, and said positional adjustment member is then rotated. By this structure, the supporting member is moved so that the distance between the LED array head and the photoconductor is adjusted, and the supporting member is mechanically fastened onto the frame by a fastening screw and nut. However, since the supporting member and the positional adjustment member are not in firm contact with each other, they are not stable. The movement of the LED array head tends to become unstable, which results in inaccurate positioning. Further, when the fastening screw and nut are fastened, the supporting member tends to be declined so that the position of the LED array head is shifted in the longitudinal direction, which tends to result in an out-of focus of the produced image. 
   SUMMARY OF THE INVENTION 
   The present invention has been achieved to overcome the above problems, and an object of the present invention is to provide a writing device, in which the positional adjustment between the LPH and the photoconductor can be easily conducted, further, any back-lash due to undesired positional adjustment and out-of-focus images are prevented. Yet further, high positional repeatability of the focus adjustment for the LED print head is obtained. 
   The object can be attained by the structure described below. 
   A writing device to write an image onto a photoconductor, includes:
         1) a print head having a plurality of LEDs arranged above and across the width of the photoconductor, which forms electrostatic latent images on the photoconductor,   (2) a first supporting member, having
           a position determining section to determine the position of the print head, and   
           an adjustment screw which is capable of being locked, in which the first supporting member allows the position determining section to come into contact with the print head and thereby supports the print head, and   (3) a second supporting member, having
           a reference shaft which comes into contact with the first supporting member and movably supports the first supporting member while moving to or separating from the photoconductor, and   a pressuring member which presses the first supporting member against the reference shaft, wherein the second supporting member is engaged with the first supporting member by the adjustment screw, whereby when the adjustment screw is rotated, the print head is shifted along with the first supporting member moving to or separating from the photoconductor so that the position of the print head is precisely adjusted, and
 
wherein a first direction which is joining the position determining section and the adjustment screw makes a right angle with a second direction which is joining the adjustment screw and the reference shaft.
   
               

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an image forming apparatus on which the writing device of the present invention is applied. 
       FIG. 2  is a front view to show assembling of the LPH and a mechanical structure of the positional adjustment of the LPH. 
       FIG. 3(   a ) is a plane view viewed in a direction of arrow Ya in  FIG. 2 . 
       FIG. 3(   b ) is an enlarged view of a portion of  FIG. 3(   a ). 
       FIG. 4  is a side view viewed in a direction of arrow Xa in  FIG. 2 . 
       FIG. 5  is a rear view viewed in a direction of arrow Za in  FIG. 4 . 
       FIG. 6  is an exploded isometric view to show a LPH and a mechanical structure of the positional adjustment of the LPH. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The embodiments of the present invention will now be detailed while referring to the drawings, but the present invention will not be limited to these embodiments. 
     FIG. 1  is a drawing showing an example of the image forming apparatuses onto which the writing device of the present invention can be applied. The image forming apparatus relating to the present invention is not limited to the embodiments detailed below. 
   The present image forming apparatus is structured of printer section GH and image reading device YS. 
   Printer section GH is called a “tandem type color image forming apparatus”, which is structured of image forming sections  10 Y,  10 M,  10 C and  10 K, intermediate transfer body  6 , being a belt, transfer section  7 A, sheet supplying section  20 , and fixing device  9 . 
   Image reading device YS, structured of automatic document feeding device  501  and scanning exposure device  502 , is installed above printer section GH. Document sheet “d”, placed on a document platen of automatic document feeding device  501 , is conveyed by a conveyance section, after which images carried on a single surface or on both surfaces of document sheet d is scanned and exposed by an optical system of scanning exposure device  502 , whereby the images are read by line image sensor CCD. 
   Signals, which have been photo-electrically converted by line image sensor CCD, are processed, employing such as an analog process, an A/D conversion process, a shading process, and an image compressing process, after which said signals are sent to LPHs  3 Y,  3 M,  3 C and  3 K, which serve as the writing device. 
   Image forming section  10 Y, which forms yellow toner images, has charging section  2 Y, writing device  3 Y structured of the LPHs, developing device  4 Y, and cleaning section  8 Y, all of which are arranged around photoconductor  1 Y. 
   Image forming section  10 M, which forms magenta toner images, has charging section  2 M, writing device  3 M structured of the LPHs, developing device  4 M, and cleaning section  8 M, all of which are arranged around photoconductor  1 M. 
   Image forming section  10 C, which forms cyan toner images, has charging section  2 C, writing device  3 C structured of the LPHs, developing device  4 C, and cleaning section  8 C, ail of which are arranged around photoconductor  1 C. 
   Image forming section  10 K, which forms black toner images, has charging section  2 K, writing device  3 K structured of the LPHs, developing device  4 K, and cleaning section  8 K, all of which are arranged around photoconductor  1 K. 
   In addition, developing devices  4 Y,  4 M,  4 C and  4 K include a dual component developer including toners of yellow (Y), magenta (M), cyan (C) and black (K), and carriers. 
   Intermediate transfer body  6  is entrained about a plurality of rollers so that it can rotate. 
   Fixing device  9  includes fixing roller  93 , having a heater and pressure roller  94  to press against fixing roller  93 . Fixing roller  93  and pressure roller  94  nip sheet P carrying the toner images so that the toner images are fixed by the heat and pressure. 
   Each color toner image, formed by image forming sections  10 Y,  10 M,  10 C and  10 K, is primarily and sequentially transferred onto rotating intermediate transfer body  6  by transfer section  7 Y,  7 M,  7 C and  7 K, so that each color image is superposed, and a full color image is formed on intermediate transfer body  6 . 
   Recording sheets P, stored in sheet supplying cassette  21 , are sequentially conveyed by sheet supplying rollers  22  of sheet supplying section  20 , and are conveyed via paired sheet supplying rollers  23  to paired registration rollers  24 , which are in a stopped status. Sheet P temporarily stops there, after the leading edge of sheet P and the toner image on transfer body  6  are made to synchronously meet each other, paired registration rollers  24  start to rotate so that sheet P is conveyed to transfer section  7 A, where a color image is transferred onto recording sheet P, which is the secondary transfer operation. Sheet P, onto which the color image has been transferred, is heated and pressed at fixing device  9 , so that the full color image is fixed onto sheet P. Then, sheet P is ejected by paired ejection rollers  25  onto sheet ejection tray  26 , attached to the outside of the apparatus. 
   Concerning intermediate transfer body  6  which has already transferred the full color toner image onto sheet P via transfer section  7 A, any remaining toner on intermediate transfer body  6  is cleaned via cleaning section  8 A. 
   The above explanation is for the color image forming apparatus, however the present invention is also applicable to a monochromatic image forming apparatus. 
   For fixing device  9 , a heated roller fixing device is used in the present embodiment, however, a belt fixing device can also be used. 
   Next, precise positional adjustment of the LPH of the writing device will be detailed while referring to  FIGS. 2-5 . 
   Since writing devices  3 Y,  3 M,  3 C and  3 K have an identical structure, and photoconductors  1 Y,  1 M,  1 C and  1 K also have an identical structure, an example is shown in which a simple numeral  3  represents any writing device, and numeral  1  represents any photoconductor. 
     FIG. 2  is a front view of LPH  301  of writing device  3 , in which a mechanical structure of the positional adjustment of LPH  301  is illustrated. Only one side of writing device  3  (which is the deepest section in the depth direction of  FIG. 1 ) is shown in  FIG. 2 , but an opposite section (which is the rear side in  FIG. 1 ) also has the same structure.  FIG. 3(   a ) is a plane view viewed in the direction of arrow Ya in  FIG. 2 , in which the head section of adjustment screw  322  is not illustrated.  FIG. 3(   b ) is an enlarged view of a portion of  FIG. 3(   a ).  FIG. 4  is a side view viewed in the direction of arrow Xa in  FIG. 2 , and  FIG. 5  is a rear view viewed in the direction of arrow Za in  FIG. 4 . 
     FIG. 6  is an exploded isometric view to show a LPH  301  and a mechanical structure of the positional adjustment of the LPH  301 . 
   In  FIG. 2 , photoconductor  1  is supported by a supporting section (which is not illustrated) mounted on frame  101 , and said photoconductor  1  is rotated by a driving section (which is also not illustrated). 
   LPH  301  is supported by second supporting member  321  mounted on frame  101  via first supporting member  311 . 
   First supporting member  311  is supported by reference shaft  325  (which is not shown in  FIG. 2 ) provided on second supporting member  321 . That is, in  FIG. 3(   a ), pressuring spring  314 , being a plate spring, which is a pressuring member and provided within first supporting member  311 , pushes reference shaft  325  in the direction shown by arrow Za, whereby contacting sections  311   a  and  311   b  of first supporting member  311 , and contacting section  314   a  of pressuring spring  314  come into contact with reference shaft  325 . Due to these contacting sections, supporting member  311  is supported by reference shaft  325 . 
   Clearances [which are shaded portions in  FIG. 3(   b )] between reference shaft  325  and first supporting member  311 , which are other than between reference shaft  325  and two sections, being contacting sections  311   a  and  311   b , and between reference shaft  325  and an one section, being pressuring spring  314 , are preferably 2 mm or less. Because, when reference shaft  325  is locked after the position of LPH  301  has been adjusted, locking agents are inserted in the clearance gaps to lock the adjusted position of reference shaft  325 , whereby the amount of the locking agents can be reduced and prevented from leaking from said clearance gaps, further, filling work of the locking agents into the clearances becomes easier. Additionally, since there are three contacting sections with reference shaft  325 , the surface area to contact with the locking agent can be increased. 
   Adjustment screw  322 , which allows first supporting member  311  to move to or separate from photoconductor  1  in direction Y, rotatably engages first supporting member  311 . 
   Reference shaft  325  and adjustment screw  322  are arranged in first direction Z as shown in  FIG. 3(   a ). 
   In  FIG. 2 , in the axial-directional position of adjustment screw  322 , first supporting member  311  is controlled by the head section of adjustment screw  322  and restriction shaft  324  fixed onto adjustment screw  322 . Pressure applying spring  323 , being an elastic member, is mounted between restriction shaft  324  and first supporting member  311 , to apply pressure against adjustment screw  322 . Due to this structure, all play is prevented from occurring in the axial direction of adjustment screw  322  of first supporting member  311 , and adjustment screw  322  can be rotated smoothly. Pressure applying spring  323  is listed as a blade spring, a spring washer and the like. 
   Since the screw section of adjustment rivet  322  mates with a threaded hole of second supporting member  321 , first supporting member  311  and second supporting member  321  are engaged with each other, with adequate clearance. When adjustment screw  322  is rotated, first supporting member  311 , which is supported by reference shaft  325 , is driven against or separated from photoconductor  1 , so that the position of first supporting member  311  is precisely controlled. In addition, when the position is controlled again in the market, the above described locking agents can be broken, if adjustment screw  322  needs to be rotated. 
   In  FIG. 3(   a ), through-hole  311 C, which engages adjustment screw  322  of first supporting member  311 , preferably has a larger diameter in first direction Z. Because first supporting member  311  is pressed against reference shaft  325 , so that the position of first supporting member  311  is restricted, therefore said through-hole  311 C is formed to be a long hole, providing clearance in first direction Z. 
   The pitch of adjustment screw  322  is preferably 0.5 mm or less. The moving length of supporting member  311  moved by a single rotation of adjustment screw  322  is set at most to 0.5 mm in direction Y in  FIG. 2 , which is preferable for precise adjustment. 
   As described above, in order to support first supporting member  311 , pressuring spring  314  presses against reference shaft  325 , adjustment screw  322  is controlled to allow no play nor to angle due to the back lash, while movement. 
   LPH  301  has engaging hole  315  which engages a ball section at the top of LPH&#39;s position determining shaft  312 , which is provided on first supporting member  311 , to serve as a position determining section. The position of LPH  301  is determined by the engagement of engaging hole  315  and the top of LPH&#39;s position determining shaft  312 , where LPH  301  is supported by first supporting member  311 . LPH&#39;s position determining shaft  312  and adjustment screw  322  are arranged in second direction X which is perpendicular to first direction Z in  FIG. 3(   a ). 
   Further in  FIG. 2 , LPH  301  has rotation preventing pin  301   a , which projects upward, so that when said rotation preventing pin  301   a  engages on-LPH supporting plate  302 , any rotation of LPH  301  is prevented. One end of holding spring  303 , serving as an elastic member, is supported by on-LPH supporting plate  302 . LPH  301  is pressed against first supporting member  311  by the other end of holding spring  303 , so that LPH  301  and first supporting member are integrally supported. 
   When adjustment screw  322  is rotated, first supporting member  311  is driven against or separated from photoconductor  1  so that the positional adjustment of LPH  301  is precisely adjusted. 
   when the above adjustment operation of LPH  301  is conducted by the rotation of adjustment screw  322  mounted through first supporting member  311 , LPH  311  is slightly declined (which is 0.1 mm or less) in first direction Z, due to the frictional resistance of the contacting points between reference shaft  325  and first supporting member  311 . Since LPH  301  is structured of the LED arrays in which a plurality of very minute LEDs are arranged, even though said decline is very slight in the longer direction of LPH  301 , out-of-focus can occur, which results in unacceptable image quality. 
   To overcome this problem, in the present invention, as described above, first direction Z, which is from reference shaft  325  to adjustment screw  322 , makes a right angle with second direction X, which is from LPH&#39;s position determining shaft  312  to adjustment screw  322 . Accordingly, the present invention includes a structure in which any decline of first supporting member  311  in first direction Z has no adverse influence upon direction X. Any out-of-focus phenomenon, which is due to decline of first supporting member  311  in direction Z, is prevented by this structure, and thereby, the high quality of formed images is maintained. Further, though the focal position is very slightly shifted on the circumference of photoconductor  1 , it has no adverse influence on the demanded high image quality. 
   That is, the writing device can be created in which the position of PLH is adjusted with an accuracy which is superior to the manufacturing accuracy of the mechanical parts, and which incorporates the LPH&#39;s positional adjustment mechanism which does not cause any adverse change of the LPH&#39;s position with age. Further, since an adjusting method using an adjustment screw is employed, precise adjustment is easily attained, and when the demanded high image quality, such as in the case of print-on-demand, optimum adjustment, matched to an individual LED and photoconductor, can be conducted in the field. 
   Based on the structure of the present invention, the first supporting member is supported by the reference shaft and the first supporting member is moved to or separated from the photoconductor, further, the first supporting member is pressed against the reference shaft by the pressuring member, whereby any play due to backlash in the adjustment screw is prevented, and precise adjustment is easily conducted. Further, since the first direction which is from the position determining section to the adjustment screw makes a right angle with the second direction, which is from the adjustment screw to the reference shaft, the inclination of the second direction, caused by the movement of the first supporting member during adjustment, is prevented from any affects on the first direction. Due to these effects, the inclination of the second direction does not adversely affect on focusing of the LPH, and out-of focus images are prevented.