Abstract:
A light scanning device for performing laser beam scanning, which includes a polygon scanner configured to deflect a laser beam; an optical device configured to guide the deflected laser beam; a case in which the polygon scanner and the optical device are arranged; a transparent covering member which is provided on the case to cover an opening and which transmits the laser beam to perform laser beam scanning; and a cleaner which is detachably attached to the light scanning device and which includes an elastic cleaning member on one side of a body of the cleaner for cleaning a surface of the transparent covering member, wherein the body of the cleaner has a recessed portion on the one side thereof.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a light scanning device which writes an electrostatic image on an image bearing member, and more particularly to a light scanning device which writes an electrostatic image on an image bearing member by scanning an image bearing member with a light beam deflected by a light deflector. 
   2. Discussion of the Background 
   Image writing sections of image forming apparatuses such as digital copiers, printers and facsimile machines include an optical image writing unit (i.e., a light scanning device) which scans an image bearing member such as photoreceptors with a light beam, which is modulated according to image signals and which is deflected by a light deflector and passes through an optical device, to form an electrostatic image on the image bearing member. The thus formed electrostatic image is developed with a developer including a toner to form a toner image on the image bearing member. 
   Recently, a need exists for an image forming apparatus, which can produce high quality images, and therefore, a need exists for a light scanning device, which can write an optical image with high resolution. Light scanning devices typically emit a laser light beam through a transparent covering member covering a light irradiation opening (e.g., dust-proof glass plates), which is provided to prevent dust from entering the light scanning devices. When toner particles and dust (such as paper dust) are adhered to the transparent material, a problem in that transmission of a laser beam is worsened and thereby qualities of an electrostatic image formed on the image bearing member are deteriorated occurs. 
   On the other hand, a need exists for a small-sized image forming apparatus. Therefore, arrangement of a light scanning device in image forming apparatuses becomes diversified. For example, there is a case where a light scanning device is arranged so as to be on the same level in position as that of an image bearing member or to be located below an image bearing member. In this case, a problem in that toner particles used for developing an electrostatic image on the image bearing member are adhered to the transparent covering member easily occurs. 
   In attempting to solve the problem, published unexamined Japanese patent application No. 2002-267983 (hereinafter referred to as JP-A) discloses a technique in that a dust-protective cover is provided on the transparent dust-proof glass plate such that dust is not adhered to the dust proof glass plate. If dust is adhered to the glass plates, the dust-proof glass is cleaned after detaching the cover therefrom, and a technique in that a cleaning mechanism for cleaning the dust-proof glass is provided to remove dust adhered to the dust-proof glass with a cleaning pad thereof. 
   JP-As 2002-127495 and 09-80875 have disclosed a technique in that the transparent covering member (made of a glass plate) has a constitution so as to be detached from the light scanning device, and a technique in that a slidable flame having a cleaning member is provided to clean the dust-proof glass. 
   Further, JP-As 2004-17607 and 07-128959 have disclosed a technique in that a bar cleaner having a pad thereon is provided or a technique in that a bar cleaner is provided on the case of a magazine of the image forming apparatus, and the surface of the transparent covering member is cleaned by the cleaner when the magazine is detached to be replaced. 
   However, recently in order to produce high quality images, a toner having a small average particle diameter is typically used and therefore the problem in that the transparent covering member of the light scanning device is contaminated with the toner is caused more frequently than ever. Particularly, spherical toner has poor cleaning property, i.e., spherical toner particles easily pass through a cleaning blade, resulting in increase of the amount of residual toner particles on an image bearing member. Therefore, the chance of contamination of a transparent covering member with residual toner particles is increased. 
   In addition, recently there is a tendency such that users perform maintenance of their image forming apparatus as much as they can. Therefore, the above-mentioned problem is easily caused. 
   Because of these reasons, a need exists for a light scanning device which can maintain good laser light emitting property over a long period of time by means of user&#39;s simple cleaning operation. 
   SUMMARY OF THE INVENTION 
   As a first aspect of the present invention, alight scanning device for performing laser beam scanning is provided which includes: 
   a polygon scanner configured to deflect a laser beam; 
   an optical device configured to guide the laser beam; 
   a case containing the polygon scanner and the optical device therein; 
   a transparent covering member which is provided on the case and which transmits the laser beam to perform laser beam scanning; and 
   a cleaner which is detachably attached to the light scanning device and which has an elastic cleaning member on one side of a body thereof for cleaning the surface of the transparent covering member, wherein the cleaner has a recessed portion on the side thereof. 
   By forming such a recessed portion, occurrence of a problem in that dust adhered to the transparent covering member is adhered to the cleaner before the dust is removed to the elastic cleaning member and the dust is adhered again to the covering member can be prevented. 
   As another aspect of the present invention, an image forming apparatus is provided which includes: 
   an image bearing member configured to an electrostatic latent image thereon; 
   a light scanning device configured to scan the image bearing member with a laser beam to form the electrostatic latent image on the image bearing member; 
   a developing device configured to develop the electrostatic latent image with a developer including a toner to form a toner image on the image bearing member; 
   a transfer device configured to transfer the toner image onto a receiving material; and 
   a fixing device configured to fix the toner image on the receiving material, 
   wherein the light scanning device is the light scanning device mentioned above. 
   These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view illustrating an example of the image forming apparatus of the present invention; 
       FIGS. 2 and 3  are schematic views for explaining the way to determine the shape factors SF- 1  and SF- 2  of toner; 
       FIG. 4  is a schematic view illustrating an example of the light scanning device of the present invention, which is arranged in the vicinity of photoreceptors; 
       FIG. 5  is a schematic perspective view illustrating the light scanning device illustrated in  FIG. 4 ; 
       FIG. 6  is a schematic perspective view illustrating the tip portion of a cleaner for use in the light scanning device of the present invention; 
       FIG. 7  is a schematic perspective view illustrating a portion of the case of the light scanning device, from which the cleaner is inserted; 
       FIGS. 8A and 8B  are schematic views illustrating the tip portions of cleaners for use in the present invention, which are set on the light scanning device; 
       FIG. 9A  is a schematic view illustrating the tip portion of the cleaner illustrated in  FIG. 6 , which is not set on the light scanning device; 
       FIG. 9B  is a schematic view illustrating the tip portion of the cleaner illustrated in  FIG. 6 , which is set on the light scanning device; 
       FIG. 10  is a schematic view for explaining how a cleaner for use in the present invention cleans the surface of the light scanning device; and 
       FIGS. 11A and 11B  are schematic views illustrating the entire of the cleaner illustrated in  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will be explained referring to drawings. 
     FIG. 1  is a schematic view illustrating the cross section of an example of the image forming apparatus of the present invention, which is a color printer. 
   Referring to  FIG. 1 , a color printer  1  includes four printer engines  3  ( 3 Y,  3 C,  3 M and  3 K), a light scanning device  4  configured to emit light beams, and an intermediate transfer medium  5 , which are set in a main body case  2 . The printer engines  3 Y,  3 C,  3 M and  3 K form yellow, cyan, magenta and black color toner images using yellow, cyan, magenta and black color toners, respectively, and have the same configuration. The suffixes Y, C, M and K represent yellow, cyan, magenta and black colors, respectively, and are hereinafter sometimes omitted. 
   The four printer engines  3 Y,  3 C,  3 M and  3 K have the same mechanical structure. Each of the printer engines  3  includes a photoreceptor  6  serving as an image bearing member, and a charger  7  configured to charge the photoreceptor  6 , a developing device  8  configured to develop an electrostatic latent image on the photoreceptor  6  with a developer including a toner to form a toner image thereon, and a cleaner  9  configured to clean the surface of the photoreceptor  6 , which are arranged around the photoreceptor  6 . 
   The photoreceptor  6  has a drum-form, and is rotated by a driving device (not shown). The photoreceptor  6  has a photosensitive layer on the peripheral surface thereof. The charger  7  is an electroconductive roller. A charging bias is applied to the charger  7  from a power source (not shown). The charger charges the peripheral surface of the photoreceptor  6 . A light beam emitted from the light scanning device  4  and modulated according to image data scans the peripheral surface of the photoreceptor  6 , which has been charged with the charger  7 , resulting in formation of an electrostatic latent image. 
   The developing device  8  supplies a toner to the photoreceptor  6 . When the toner is adhered to the electrostatic latent image on the photoreceptor  6 , the latent image is visualized as a toner image. In this example, the toner has a first shape factor SF- 1  of from 100 to 150, and a second shape factor SF- 2  of from 100 to 140. 
     FIGS. 2 and 3  are schematic views for explaining the shape factors SF- 1  and SF- 2 , respectively. 
   As illustrated in  FIG. 2 , the shape factor SF- 1  represents the degree of the roundness of a toner and is defined by the following equation (1):
 
 SF -1={(MXLNG) 2 /(AREA)}×(100π/4)  (1)
 
wherein MXLNG represents a diameter of the circle circumscribing the image of a toner particle, which image is obtained by observing the toner particle with a microscope; and AREA represents the area of the image.
 
   When the SF- 1  is 100, the toner particle has a true spherical form. In this case, the toner particles contact the other toner particles and a photoreceptor serving as an image bearing member at one point. Therefore, the adhesiveness of the toner particles to the other toner particles and the photoreceptor decreases, resulting in increase of the fluidity of the toner particles and the transferability of the toner. When the SF- 1  is too large, the toner particles have irregular forms and thereby the toner has poor developability and poor transferability. 
   As illustrated in  FIG. 3 , the shape factor SF- 2  represents the degree of the concavity and convexity of a toner particle, and is defined by the following equation (2):
 
 SF -2={(PERI) 2 /(AREA)}×(100/4π)  (2)
 
wherein PERI represents the peripheral length of the image of a toner particle observed by a microscope; and AREA represents the area of the image.
 
   When the SF- 2  approaches 100, the toner particles have a smooth surface (i.e., the toner has few concavity and convexity). It is preferable for a toner to have a slightly roughened surface because the toner has good cleanability. However, when the SF- 2  is too large (i.e., the toner particles are seriously roughened), a toner scattering problem in that toner particles are scattered around a toner image is caused, resulting in deterioration of the toner image qualities. 
   The cleaner  9  removes toner particles remaining on the peripheral surface of the photoreceptor  6  even after a toner image formed on the photoreceptor  6  is transferred onto the intermediate transfer medium  5 . 
   The intermediate transfer medium  5  is an endless belt made of a material such as resins and rubbers. Color toner images formed on the photoreceptors  6  are transferred to the intermediate transfer medium  5 . The intermediate transfer medium  5  is rotated in a direction indicated by an arrow while stretched by rollers  10 ,  11  and  12 . Four transfer rollers  13  are arranged so as to be contacted with the inner surface of the intermediate transfer medium  5  to well transfer the toner images on the photoreceptors  6  onto the intermediate transfer medium  5 . Since the color toner images formed on the photoreceptors  6  are sequentially transferred onto the intermediate transfer medium  5 , a full color image is formed on the intermediate transfer medium  5 . A belt cleaner  14  is provided to remove toner particles and paper dust remaining on the surface of the intermediate transfer medium  5 . 
   A paper cassette  15  is arranged below the printer engines  3  and the light scanning device  4 . Sheets of a receiving material P are stocked in the paper cassette  15 . An uppermost sheet of the receiving material P is fed toward the printer engines  3  by a feeding roller  16  while separated from the other sheets. 
   The sheet of the receiving material P is fed through a passage  17 . Along the passage  17 , a pair of registration rollers  18 , a transfer roller  19 , a fixing device  20 , a pair of discharge rollers  21 , etc., are provided. 
   The pair of registration rollers  18  are rollers which are intermittently rotated in exact timing with an image forming operation of the printer engines  3 . Specifically, when the registration rollers  18  start to rotate, the sheet of the receiving material P, which has been fed to the registration rollers  18  and stopped thereat, is fed toward the transfer position, i.e., the nip between the intermediate transfer medium  5  and the transfer roller  19 . The color toner image formed on the intermediate transfer medium  5  is transferred onto the sheet of the receiving material P at the nip. 
   The fixing device  20  melts and fixes the color toner image on the sheet of the receiving material P upon application of heat and pressure thereto. The sheet of the receiving material P bearing the toner image thereon (i.e., a copy of an image) is then discharged to a tray  22 . 
     FIG. 4  is a schematic view illustrating the cross section of the light scanning device  4 .  FIG. 5  is a schematic perspective view of the light scanning device  4 . As illustrated in  FIG. 4 , the four photoreceptors  6   a ,  6   b ,  6   c  and  6   d  are provided in the vicinity of the light scanning device  4 . For example, yellow, cyan, magenta and black toner images are formed on the photoreceptors  6   a ,  6   b ,  6   c  and  6   d , respectively. However, the colors and color order are not limited thereto. 
   Needless to say, a charger (such as charging rollers, charging brushes and charging wires), a developing device, an intermediate transfer medium, a transfer device (such as transfer rollers and transfer brushes), a cleaner (such as cleaning blades and cleaning brushes) are provided around each of the photoreceptors  6   a ,  6   b ,  6   c  and  6   d  to form color images, but the devices are omitted in  FIG. 4 . The suffixes a, b, c and d represent colors of images. Since the configurations of the devices used for the four engines are the same, explanation is performed while the suffixes are sometimes omitted. 
   The light scanning device  4  is located below the four photoreceptors  6 , and has four light sources  39   a ,  39   b ,  39   c  and  39   d , each of which includes a laser diode; a light deflector which includes a polygon mirror  40  configured to symmetrically deflect four light beams emitted by the light sources  39  in opposite two directions, wherein since the polygon mirror  40  has upper and lower mirrors, the paths of the two light beams deflected in the same direction are different from each other; and a transmission/focusing optical device which includes a fθ lens  43 , a focusing lens  44  and mirrors  45 ,  46  and  47 , which are configured to guide and focus the light beams on the surfaces of the respective photoreceptors. These element is are set within the case of the light scanning device  4 . In  FIG. 4 , numeral  49  denotes a light beam. 
   The light scanning device  4  has side walls  42  which is connected with a base plate supporting the transmission/focusing optical device and surrounds the transmission/focusing optical device. In addition, the base plate separates the upper portion from the lower portion of the light scanning device  4  as illustrated in  FIG. 4 . As illustrated in  FIG. 5 , the four light sources  39  are provided on the side wall. The polygon mirror  40  is arranged on a recessed portion of the base plate, which portion is located in substantially the center of the light scanning device  4 . Thus, the light scanning device is closed. Therefore, the light scanning device has four laser light emitting openings (i.e., exits) on an upper case  41 , on which four transparent dust-proof glass plates  48   a ,  48   b ,  48   c  and  48   d  are provided. 
   The light scanning device  4  converts image data, which are input from a document reader (not shown), or an image data output device such as personal computers, word processors, and receivers of facsimiles and which are subjected to a color separation treatment, to signals for driving the light sources, resulting in emission of light beams having image information. The thus emitted light beams are guided to the polygon mirror  40  to be deflected and scanned. 
   In  FIG. 4 , the polygon mirror  40  has two thin upper and lower mirrors, wherein the upper mirror deflects the light beams  49   a  and  49   d  for irradiating the photoreceptors  6   a  and  6   d , and the lower mirror deflects the light beams  49   b  and  49   c  for irradiating the photoreceptors  6   b  and  6   c . However, the polygon mirror is not limited thereto. For example, a polygon mirror having one mirror with large thickness in the axial direction thereof can also be used. Each of the thus deflected light beams pass through openings  38 , the fθ lens  43  and the focusing lens  44 , and is then reflected by the mirrors  45 ,  46  and  47 . Then the light beam  49  passing through the dust-proof glass plate  48  scans the surface of the photoreceptor  6 , resulting in formation of electrostatic latent images on the photoreceptors  6 . The thus formed electrostatic latent images are developed with respective developers which is included in the developing devices  8  each including a color toner, resulting in formation of different color toner images on the respective photoreceptors  6 . The toner images are transferred one by one to the intermediate transfer medium  5  by the transfer rollers  13 . The thus overlaid color toner images are then transferred to the receiving material P at the same time. The multi-color toner image is then fixed by the fixing device  20 , resulting information of a color copy. 
     FIG. 6  is an enlarged view illustrating the tip portion of the cleaner for cleaning the dust-proof glass plate  48 .  FIG. 7  is an enlarged view illustrating the portion of the light scanning device, from which the cleaner is inserted to clean the dust-proof glass plate  48 . Referring to  FIG. 6 , a cleaner  50  includes a cleaning member  51 , a recessed portion  52   a , a projected portion  52   b , and a guide  53 . In  FIG. 7 , numeral  54  denotes an L-form guide for guiding the guide  53 , and numeral  55  denotes an engaging portion which has substantially the same structure as the L-form guide  54  except that the height and width thereof are greater than those of the L-form guide  54  so that the guide  53  can be easily inserted thereinto. 
   Then the cleaning operation of the cleaner  50  for the dust-proof glass plate  48  will be explained. At first, the guide  53  of the cleaner  50  is engaged with the engaging portion  55  to be inserted thereinto. The cleaner  50  is then fed in a direction indicated by an arrow as illustrated in  FIG. 7  while guided by the plurality of L-form guides  54 , which are arranged at regular intervals. Thus, the surface of the dust-proof glass plate  48  is cleaned by the cleaning member  51 . In this regard, since the length of the cleaner  50  is longer than that of the dust-proof glass plate  48 , the entire surface of the dust-proof glass plate  48  can be subjected to the cleaning treatment. 
     FIGS. 8A and 8B  are schematic views illustrating examples of the tip portion of the cleaner, which is set above the dust proof glass plate  48 . As illustrated in  FIG. 8A , the cleaner is set such that the recessed portion  52   a  of the body thereof is not contacted with the surface of the glass plate  48 . In addition, the recessed portion has a width (A) of longer than a width (C) of the cleaning member  51 . In this cleaner  50 , only the cleaning member  51  is contacted with the surface of the glass plate  48  to be cleaned, i.e., other portions of the cleaner  50  are prevented from contacting with the surface of the glass plate  48  to be cleaned. By using such a cleaner, occurrence of a problem in that dust on the surface of the glass plate  48  is adhered to other portions of the cleaner, and the dust is re-transferred to the surface of the glass plate  48  to be cleaned can be prevented. 
   As illustrated in  FIG. 8B , the cleaner  50  may have a configuration such that the width (A) of the recessed portion is longer than the width (C) of the cleaning member  51  and shorter than a width (B) of the glass plate  48 . In this cleaner  50 , the surface of the projected portion  52   b  of the body of the cleaner is contacted with the surface of the glass plate  48 , and therefore the position of the cleaning member  51  relative to the surface of the glass plate  48  can be well controlled. Therefore, the surface of the glass plate  48  can be uniformly and effectively cleaned. 
     FIG. 9A  is across section of the tip portion of the cleaning member  51  of the cleaner  50 .  FIG. 9B  is a cross section of the tip portion when the cleaning member is contacted with the dust-proof glass plate  48  to clean the surface of the glass plate. 
   As illustrated in  FIG. 9A , the cleaning member  51  is a blade made of an elastic material such as felt, sponge and rubbers (such as polyurethane rubbers). One end of the cleaning member  51  is fixed to the body of the cleaner  50  so as to be slanted at an angle of from 20 to 30° relative to the surface of the glass plate  48 . In addition, as illustrated in  FIG. 9B , the cleaner  50  has a space  56 . When the cleaning member  51  is contacted with the surface of the glass plate  48 , the cleaning member  51  is deformed so as to enter into the space  56  (i.e., to be stored in the space  56  without contacted with other portions of the cleaner) as illustrated in  FIG. 9B . Therefore, the cleaning member  51  can be contacted with the surface of the glass plate  48  at substantially a constant pressure, and thereby the surface of the glass plate  48  can be well cleaned without causing uneven cleaning due to irregular deformation of the blade. 
     FIG. 10  is a schematic view for explaining the angle of the cleaning member  51  when the cleaning member is contacted with the glass plate  48 . When the cleaner  50  is moved in a drawing direction to be drawn from the light scanning device  4 , the angle formed by the upper surface of the cleaning member  51  and the upper surface of the dust-proof glass plate  48  is preferably greater than 90° (i.e., an obtuse angle) as illustrated in  FIG. 10 . When the cleaner  50  has such a configuration, the cleaner can be easily inserted into the light scanning device  4 . Further, when the cleaner  50  is drawn from the light scanning device  4  after the cleaning operation, the cleaning member  51  is contacted with the glass plate  48  so as to counter the glass plate, and therefore the surface of the glass plate can be well cleaned and the collected dust can be securely swept out from the light scanning device  4 . Thus, an effective cleaning operation can be performed. 
     FIGS. 11A and 11B  are an elevational view and a side view of the cleaner  50 , respectively. Referring to  FIGS. 11A and 6 , double ribs  57   a  are formed on a tip portion (D) of the cleaner  50 , and a single rib  57   b  is formed on the other portion of the cleaner. Therefore, the tip portion (D) has a greater rigidity than the other portion. In addition, the tip portion (D) is bent toward one side thereof, on which the cleaning member  51  is provided, as illustrated in  FIG. 11B . Further, it is preferable that the distance between a center (E) of the tip portion D and a tip (T) of the cleaner  51  is longer than the interval between two adjacent L-form guides  54  illustrated in  FIG. 7 . Since the tip portion (D) has a higher rigidity than the other portion, the cleaner  50  can be easily inserted into the light scanning device  4  if the guide  53  is engaged with the engaging portion  55  of the light scanning device  4  as illustrated in  FIGS. 6 and 7 . 
   In addition, since the tip portion (D) of the cleaner  50  is bent and the distance between the center (E) and the tip (T) of the cleaner is longer than the interval between two adjacent L-form guides  54 , the cleaning member can be contacted with the surface of the dust-proof glass plate  48  at substantially a constant pressure. Specifically, when the center (E) is located at the center between two adjacent L-form guides  54 , the tip (T) of the cleaner can be pressed by the bending force of the cleaner. When the center (E) is located below one of the L-form guides  54 , the tip (T) of the cleaner can be pressed by another one of the L-form guides  54 . Therefore, the cleaning member  51  can be always contacted with the dust-proof glass plate  48  at substantially a constant pressure. In  FIG. 11A , numeral  58  denotes a handle portion. 
   Thus, the surface of the dust-proof glass plate  48  can be securely cleaned well even by users. Therefore, the original performance of the light scanning device and the image forming apparatus can be maintained over a long period of time. 
   Even when a spherical toner is used to produce high quality images, the toner particles adhered to the glass plate can be well removed therefrom by the cleaner. Therefore, the original performance of the light scanning device and the image forming apparatus can be maintained over a long period of time. In addition, the light scanning device can be freely set in the image forming apparatus without constraints. 
   This document claims priority and contains subject matter related to Japanese Patent Application No. 2005-218852, filed on Jul. 28, 2005, incorporated herein by reference. 
   Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth therein.