JP2005300815A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To hardly give rise to contrast unevenness and color unevenness of images by compensating the nonuniformity of the light power distribution of a light beam spot in a horizontal scanning direction due to staining of reflective surfaces of rotary polygon mirrors of optical scanning arrangements used for exposing devices by the dependence of the reflectivity to the reflective surfaces on incident angles. <P>SOLUTION: The image forming apparatus is provided with at least one or more of image forming stations disposed with electrostatic charging means, exposing means, developing means, and transferring means around an image carrier and transfers the toner images formed in such image forming stations to transfer media, wherein the optical scanning arrangements using the rotary polygon mirrors 1 as deflection reflective surfaces are used for the exposing means and the polarization directions of the incident light on the respective deflection reflective surfaces of the rotary polygon mirrors 1 of the optical scanning arrangements are so set as as to constitute approximately P polarized light and are so set as to make the light 15 incident on the respective deflection reflective surfaces of the rotary polygon mirrors from the deflection upstream side of the deflection light beams 16 by the rotary polygon mirrors 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that hardly causes in-plane optical power unevenness even when the reflecting surface of a rotary polygon mirror used in an exposure apparatus becomes dirty, and is less likely to cause unevenness in color shading or color unevenness. Is.

  In an optical scanning device using a rotating polygon mirror (polygon mirror), dust in the air collides and adheres to the reflecting surface of the rotating polygon mirror as the usage time elapses, resulting in contamination. The reflectivity decreases due to the dirt, so that the optical power of the light beam spot on the scanned surface is reduced. However, since the dirt on the reflecting surface is not uniform in each reflecting surface, the main scanning direction of the scanned surface is reduced. Also, the optical power distribution is non-uniform. While the electrophotographic laser printer using such an optical scanning device is continuously used, unevenness of the image and unevenness of color due to such non-uniformity of the optical power distribution occurs.

  Conventionally, as a means for preventing unevenness of the optical power distribution due to the contamination of the reflecting surface of the rotating polygon mirror, a method of sealing the rotating polygon mirror has been used. Inevitably, unevenness of color and unevenness of color occurred as time passed.

  The present invention has been made in view of such problems of the prior art, and the object thereof is a light beam spot in the main scanning direction caused by dirt on the reflecting surface of the rotary polygon mirror of the optical scanning device used in the exposure apparatus. Is to compensate for the non-uniformity of the light power distribution by the dependence of the reflectance on the reflecting surface on the incident angle, thereby making it difficult for unevenness of color and unevenness of color to occur.

The image forming apparatus of the present invention that achieves the above object is provided with at least one image forming station in which a charging unit, an exposure unit, a developing unit, and a transfer unit are arranged around an image carrier, and is formed by the image forming station. In the image forming apparatus for transferring the toner image to the transfer medium,
An optical scanning device using a rotating polygon mirror as a deflection reflection surface is used for the exposure means,
When the rotary polygon mirror of the optical scanning device rotates in the air containing the contaminant, the contaminant adheres unevenly to each deflecting reflection surface of the rotary polygon mirror and the in-plane reflectance becomes non-uniform. The rotation direction of the rotary polygon mirror and the incident position of the incident light on the deflecting reflecting surface are set so as to compensate for this with the dependence of the reflectance on the incident angle of the deflecting reflecting surface. Is.

Another image forming apparatus according to the present invention includes at least one image forming station in which a charging unit, an exposure unit, a developing unit, and a transfer unit are arranged around an image carrier, and a toner formed by the image forming station. In an image forming apparatus for transferring an image to a transfer medium,
An optical scanning device using a rotating polygon mirror as a deflection reflection surface is used for the exposure means,
The polarization direction of the incident light to each deflection reflection surface of the rotary polygon mirror of the optical scanning device is set to be substantially S-polarized light, and each of the rotary polygon mirrors from the deflection downstream side of the deflection light beam by the rotary polygon mirror It is characterized in that it is set so that light enters the deflecting reflecting surface.

Still another image forming apparatus according to the present invention includes at least one image forming station in which a charging unit, an exposure unit, a developing unit, and a transfer unit are arranged around an image carrier, and is formed by the image forming station. In an image forming apparatus for transferring a toner image to a transfer medium,
An optical scanning device using a rotating polygon mirror as a deflection reflection surface is used for the exposure means,
The polarization direction of the incident light on each deflection reflection surface of the rotary polygon mirror of the optical scanning device is set to be substantially P-polarized light, and each of the rotary polygon mirrors from the upstream side of deflection of the deflection light beam by the rotary polygon mirror It is characterized in that it is set so that light enters the deflecting reflecting surface.

  In the above, the present invention is suitable when the optical scanning device is disposed substantially below the developing unit in the direction of gravity.

  In the present invention, the rotating polygon mirror used in the optical scanning device of the exposure means rotates in the air containing the contaminant, so that the contaminant adheres unevenly to each deflecting reflecting surface of the rotating polygon mirror. The rotation direction of the rotating polygon mirror and the incident position of incident light on the deflecting reflecting surface are set so as to compensate for the non-uniform reflectance of the reflecting mirror depending on the dependency of the reflecting angle on the incident angle of the deflecting reflecting surface. Therefore, it is difficult for image unevenness and color unevenness to occur due to the nonuniformity of the light power distribution with the passage of time of use.

  The basic principle of the optical scanning device used in the image forming apparatus of the present invention is to complement the incident angle dependence of the reflectance on the reflecting surface of the rotating polygon mirror and the position dependence of the reflectance due to dirt on the reflecting surface. Thus, the polarization of the light from the light source is selected, and the incident direction to the reflection surface of the rotary polygon mirror is selected.

  As shown in FIG. 5, when the rotating polygonal mirror 1 rotates as indicated by an arrow, the surrounding air flows relative to each reflecting surface 2 in the direction opposite to the reflecting surface rotation direction to become an air flow 4. However, it becomes a turbulent flow on the downstream side of the edge portion 3 at the boundary between the reflecting surfaces 2 and 2 adjacent to each other, and dust and dust contained in the air flow 4 are involved and collide with each reflecting surface 2. In particular, the downstream side (the front end side in the rotational direction of the reflecting surface 2) 2 'of the boundary edge portion 3 is significantly soiled. The fact that the downstream side 2 ′ of the boundary edge portion 3 is dirty means that the upstream side of the deflection, that is, the writing start side of the light beam in the main scanning direction is dirty, and the laser printer is being used continuously. Thus, the optical power of the light beam spot on the writing start side is lowered.

  FIG. 6 shows a decrease in the amount of reflected light depending on the position on the reflecting surface due to dirt on each reflecting surface 2 of the rotary polygon mirror 1 operated for a certain time. The position on the reflecting surface on the horizontal axis indicates the writing start position by the scanning light beam as 0 and the writing end position as 1, and the vertical axis indicates the relative value of the reflected light amount. Measurement was performed at the same incident angle.

  On the other hand, when the reflecting surface 2 of the rotary polygon mirror 1 is a reflecting surface obtained by coating a metal reflecting surface with a protective film, as shown in FIG. The reflectance increases as the angle (with respect to) increases, and the reflectance decreases with P-polarized light. This tendency is the same when the reflecting surface 2 is constituted by a metal reflecting mirror not coated with a protective film.

  Therefore, in the present invention, depending on the polarization direction of the light incident on the deflecting / reflecting surface 2 of the rotary polygon mirror 1, the deflected light beam is incident from the upstream side or the downstream side of the deflected light beam, and the writing start side in FIG. The decrease in the optical power of the light beam spot is compensated by the incident angle dependence of the reflectivity in FIG. The specific arrangement is shown in FIGS.

  1 and 2, an optical scanning device according to the present invention includes, as an example, a light source 11, an illumination lens 12, a rotary polygon mirror 1, a scanning optical system 13, and a surface to be scanned (in the case of an electrophotographic laser printer, a photoconductor). The light from the light source 11 is converted into a parallel light beam by the illumination lens 12 (when surface tilt correction is performed, the light becomes parallel light in the direction perpendicular to the rotation axis of the rotary polygon mirror 1, The light beam 15 is incident on the deflecting reflecting surface 2 of the rotating polygon mirror 1 and is deflected and reflected in the direction parallel to the rotation axis). The light beam reflected and deflected by the surface 2 is converted into a deflected light beam 16 which is deflected in the direction of the arrow in the figure through the scanning optical system 13, and is incident on the surface 14 to be scanned and converged.

  The arrangement in FIG. 1 is a case where the light beam 15 incident on the deflecting reflecting surface 2 is P-polarized light (the electric field vector oscillation direction is parallel to the incident surface). In FIG. 1, a P-polarized light beam 15 is incident on the deflecting / reflecting surface 2 from the upstream side of deflection of the deflecting light beam 16, and is initially incident on the deflecting / reflecting surface 2 with a small incident angle. Then, the incident angle increases in order, and at the end of the deflection, the incident light enters the deflecting reflection surface 2 at a large incident angle. Therefore, the reflectivity at the deflecting / reflecting surface 2 is lowered (FIG. 7), but on the leading end side 2 ′ (FIG. 5) in the rotational direction of the deflecting / reflecting surface 2 where the reflectivity of the deflecting / reflecting surface 2 is significantly reduced. Since the light is incident first, the first decrease in the reflectance due to dirt on the deflecting reflecting surface 2 can be compensated by the dependency of the reflectance on the incident angle.

  FIG. 3 shows an example of the distribution of the amount of reflected light with respect to the incident angle of the light beam 15 when the polarization reflecting surface 2 of the rotary polygon mirror 1 is contaminated with dust or the like in the arrangement of FIG. In the figure, the solid line shows the distribution of the reflected light amount in the case of the arrangement of FIG. 1, and the broken line shows the reflected light amount when the light beam 15 is incident from the side opposite to FIG. 1 (the deflection downstream side of the deflected light beam 16). The distribution of. Before the polarization reflecting surface 2 of the rotary polygon mirror 1 is soiled, the distribution of the reflected light quantity corresponding to the curve of P deflection in FIG. 7 is shown. As shown in FIG. 3, the optical power of the first part of deflection (writing start side) is relatively low, the distribution is more balanced over the entire main scanning range, and the optical power distribution in the main scanning direction is more uneven. Disappears. If the light beam 15 is incident from the side opposite to that in FIG. 1 as shown by the broken line in FIG. 3, the difference in the optical power at both ends of the scanning range becomes too large, resulting in nonuniform light power distribution. It becomes conspicuous, and uneven density and uneven color easily occur.

  The arrangement in FIG. 2 is a case where the light beam 15 incident on the deflecting reflecting surface 2 is S-polarized light (the electric field vector oscillation direction is perpendicular to the incident surface). In FIG. 2, the S-polarized light beam 15 is incident on the deflecting / reflecting surface 2 from the downstream side of the deflecting light beam 16 and is initially incident on the deflecting / reflecting surface 2 at a large incident angle. Then, the incident angle decreases in order, and at the end of the deflection, the incident light enters the deflecting reflection surface 2 at a small incident angle. Therefore, the reflectivity at the deflecting / reflecting surface 2 is lowered (FIG. 7), but on the leading end side 2 ′ (FIG. 5) in the rotational direction of the deflecting / reflecting surface 2 where the reflectivity of the deflecting / reflecting surface 2 is significantly reduced. Since the light is incident first, the first decrease in the reflectance due to dirt on the deflecting reflecting surface 2 can be compensated by the dependency of the reflectance on the incident angle.

  FIG. 4 shows an example of the distribution of the amount of reflected light with respect to the incident angle of the light beam 15 when the polarization reflecting surface 2 of the rotary polygon mirror 1 is contaminated with dust or the like in the arrangement of FIG. In the figure, the solid line shows the distribution of the reflected light amount in the case of the arrangement of FIG. 2, and the broken line shows the reflected light amount when the light beam 15 is incident from the side opposite to FIG. 2 (the upstream side of deflection of the deflected light beam 16). The distribution of. Before the polarization reflecting surface 2 of the rotary polygon mirror 1 is soiled, the distribution of the amount of reflected light corresponding to the S deflection curve of FIG. 7 is shown. As shown in FIG. 4, the optical power of the first part of deflection (writing start side) is relatively low, the distribution is more balanced over the entire main scanning range, and the optical power distribution in the main scanning direction is more uneven. Disappears. If the light beam 15 is incident from the opposite side of FIG. 2 as indicated by the broken line in FIG. 4, the difference in the optical power at both ends of the scanning range becomes too large, resulting in uneven optical power distribution. It becomes conspicuous, and uneven density and uneven color easily occur.

  Note that the polarization direction (P-polarized light, S-polarized light) of the light beam 15 incident on the deflecting / reflecting surface 2 of the rotary polygon mirror 1 is such that when the light emitted from the light source 11 to be used is linearly polarized light, the polarization direction of the emitted light is When the light emitted from the light source 11 is other than linearly polarized light, the light beam 15 is adjusted so that the light beam 15 has a desired polarization direction by arranging a polarizer in the path.

  As described above, in any of the arrangements of FIGS. 1 and 2, the inclination of the initial optical power distribution and the inclination of the power distribution caused by the dirt on the reflection surface act so as to compensate for each other. In an image obtained by an electrophotographic laser printer or the like using, density unevenness and color unevenness hardly occur.

  The optical scanning device according to the present invention as described above is particularly effective when it is disposed in an environment where the image forming apparatus is easily contaminated. FIG. 8 is a schematic cross-sectional view showing the overall configuration of one embodiment of an image forming apparatus (electrophotographic laser printer) 30 using the electrophotographic process of the present invention suitable for applying the optical scanning device according to the present invention. . The image forming apparatus 30 of this embodiment uses a single image carrier (photosensitive drum) 31, and a single corona disposed around the image carrier 31 from upstream to downstream in the rotation direction. A charging means 32 comprising a charging means, an optical scanning device 20 of the present invention for repeatedly deflecting and scanning the deflected light beam 16 in the direction of the generatrix of the image carrier (photosensitive drum) 31, a yellow developing device 33Y, and a magenta developing device. 33M, a cyan developing device 33C, and a black developing device 33K are arranged with a rotary developing device 34 arranged so as to be able to rotate and rotate around the rotation center. The electrostatic latent image formed by being charged and exposed and discharged by the deflected light beam 16 from the optical scanning device 20 is one of the developing devices 33Y selected in the order of the rotary developing device 34. 33M, 33C, is developed as a toner image by 33K. The yellow, magenta, cyan, and black toner images sequentially formed in this manner are sequentially subjected to primary transfer on the intermediate transfer belt 36 sequentially by a primary transfer bias applied to a primary transfer member (transfer roller) 35. The full-color toner image that is sequentially superimposed on the intermediate transfer belt 36 is secondarily transferred to a recording medium P such as paper by a secondary transfer roller 37, and passes through a pair of fixing rollers of a fixing unit 38. The sheet is fixed on the sheet and discharged by a pair of sheet discharge rollers 39 onto a sheet discharge tray 40 formed on the upper part of the apparatus. In the figure, reference numeral 41 denotes a paper feed unit, which comprises a paper feed cassette 42 in which the recording media P are stacked and held, and a pickup roller 43 that feeds the recording media P from the paper feed cassette 42 one by one. A paper feeder is provided.

  Here, in the image forming apparatus 30, the optical scanning device 20 is disposed substantially below the gravity direction of the rotary developing device 34, so that it is easily contaminated with toner spilled from the developing devices 33Y, 33M, 33C, and 33K. Therefore, as described with reference to FIG. 5, the front end side 2 ′ in the rotation direction of each reflecting surface 2 of the rotary polygon mirror 1 is easily contaminated. Therefore, by using the optical scanning device according to the present invention for the optical scanning device 20 in such an environment, even when the usage time is considerably long, unevenness in color density and color unevenness hardly occur.

  As described above, the optical scanning device of the present invention and the image forming apparatus using the same have been described based on the principle and the embodiments. However, the present invention is not limited to these embodiments and can be variously modified.

FIG. 6 is an optical path diagram showing the arrangement of the optical scanning device according to the present invention when the light beam incident on the deflecting reflecting surface is P-polarized light. FIG. 6 is an optical path diagram showing the arrangement of the optical scanning device according to the present invention when the light beam incident on the deflecting reflecting surface is S-polarized light. FIG. 1 shows an example of the distribution of the amount of reflected light with respect to the incident angle of a light beam when the polarization reflecting surface of the rotary polygon mirror is soiled with dust, dust, etc. in the case of the arrangement of FIG. 2 shows an example of the distribution of the amount of reflected light with respect to the incident angle of the light beam when the polarization reflecting surface of the rotary polygon mirror is soiled with dust, dust, or the like in the arrangement of FIG. It is a figure for demonstrating the reason which each reflective surface of a rotary polygon mirror becomes dirty by the rotation. It is a figure which shows the fall depending on the position on the reflective surface of the reflected light quantity by the stain | pollution | contamination of each reflective surface of the rotary polygon mirror which worked for a fixed time. It is a figure which shows the dependence of the reflectance by the incident angle of the S polarized light of the reflective surface of a rotary polygon mirror, and P polarized light. 1 is a schematic cross-sectional view showing an overall configuration of an embodiment of an image forming apparatus (electrophotographic laser printer) using an electrophotographic process of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rotating polygon mirror 2 ... Polarization reflecting surface 2 '... The downstream side of a boundary edge part mainly on a reflective surface (reflective surface rotation direction front side)
3 ... Edge part 4 ... Air flow 11 ... Light source 12 ... Illumination lens 13 ... Scanning optical system 14 ... Scanned surface (photosensitive member)
15: Light beam incident on polarization reflecting surface 16: Deflection light beam 30 ... Image forming apparatus (electrophotographic laser printer)
31. Image carrier (photosensitive drum)
32 ... Charging means 20 ... optical scanning device 33Y ... yellow developing device 33M ... magenta developing device 33C ... cyan developing device 33K ... black developing device 34 ... rotary developing device 35 ... primary transfer member (transfer roller)
36 ... Intermediate transfer belt 37 ... Secondary transfer roller 38 ... Fixing unit 39 ... Paper discharge roller pair 40 ... Paper discharge tray 41 ... Paper feed unit 42 ... Paper feed cassette 43 ... Pickup roller P ... Recording medium

Claims (4)

An image forming apparatus in which at least one image forming station having a charging unit, an exposing unit, a developing unit, and a transfer unit arranged around an image carrier is provided, and a toner image formed at the image forming station is transferred to a transfer medium. ,
An optical scanning device using a rotating polygon mirror as a deflection reflection surface is used for the exposure means,
When the rotary polygon mirror of the optical scanning device rotates in the air containing the contaminant, the contaminant adheres unevenly to each deflecting reflection surface of the rotary polygon mirror and the in-plane reflectance becomes non-uniform. The rotation direction of the rotary polygon mirror and the incident position of the incident light on the deflecting reflecting surface are set so as to compensate for this with the dependence of the reflectance on the incident angle of the deflecting reflecting surface. Image forming apparatus. An image forming apparatus in which at least one image forming station having a charging unit, an exposing unit, a developing unit, and a transfer unit arranged around an image carrier is provided, and a toner image formed at the image forming station is transferred to a transfer medium. ,
An optical scanning device using a rotating polygon mirror as a deflection reflection surface is used for the exposure means,
The polarization direction of the incident light to each deflection reflection surface of the rotary polygon mirror of the optical scanning device is set to be substantially S-polarized light, and each of the rotary polygon mirrors from the deflection downstream side of the deflection light beam by the rotary polygon mirror An image forming apparatus, wherein the image forming apparatus is set so that light is incident on a deflecting reflecting surface. An image forming apparatus in which at least one image forming station having a charging unit, an exposing unit, a developing unit, and a transfer unit arranged around an image carrier is provided, and a toner image formed at the image forming station is transferred to a transfer medium. ,
An optical scanning device using a rotating polygon mirror as a deflection reflection surface is used for the exposure means,
The polarization direction of the incident light on each deflection reflection surface of the rotary polygon mirror of the optical scanning device is set to be substantially P-polarized light, and each of the rotary polygon mirrors from the upstream side of deflection of the deflection light beam by the rotary polygon mirror An image forming apparatus, wherein the image forming apparatus is set so that light is incident on a deflecting reflecting surface. The image forming apparatus according to claim 1, wherein the optical scanning device is disposed substantially below the developing unit in the direction of gravity.

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