JP2005157044A - Optical scanner and image forming apparatus furnished with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light beam scanner with which picture quality is improved. <P>SOLUTION: In the optical scanner with which a latent image is formed on a plurality of photoreceptor drums (image carriers) D<SB>1</SB>through D<SB>4</SB>arranged in a line with a pitch substantially twice a peripheral length by points LP<SB>1</SB>through LP<SB>4</SB>being irradiated with laser beams LB<SB>1</SB>through LB<SB>4</SB>, the angles α<SB>1</SB>through α<SB>4</SB>between the normal lines HL<SB>1</SB>through HL<SB>4</SB>of the irradiated points LP<SB>1</SB>through LP<SB>4</SB>and the normal lines AL<SB>1</SB>through AL<SB>4</SB>of reference points P<SB>1</SB>through P<SB>4</SB>provided on the photoreceptor drums D<SB>1</SB>through D<SB>4</SB>have one and the same value, and angles β<SB>1</SB>through β<SB>4</SB>between the irradiated points LP<SB>1</SB>through LP<SB>4</SB>being irradiated with the laser beams LB<SB>1</SB>through LB<SB>4</SB>and the normal lines HL<SB>1</SB>through HL<SB>4</SB>are given by the relations β<SB>1</SB>through β<SB>4</SB>=±2 to 10 degrees and β<SB>1</SB>=β<SB>2</SB>=-β<SB>3</SB>=-β<SB>4</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a plurality of image carriers arranged in a line, an optical scanning device that deflects and scans each image carrier with a laser beam modulated by an image signal, and an image forming apparatus including the optical scanning device.

  Conventionally, a tandem type image forming apparatus has a plurality of image forming stations provided with an image carrier inside, arranged in a row, and electrostatically adsorbs recording paper on a conveyance belt, and sequentially contacts each station. Paper transport system that applies an electrostatic transfer force between the station and the recording paper while transferring the toner image, and transfers the color images while directly transferring the toner images to the recording paper. A plurality of formation stations are arranged in a row, and an electrostatic transfer force is applied between each station and the intermediate transfer belt while conveying the intermediate transfer belt formed of a dielectric material in contact with each station. Are applied in order to perform primary transfer, color superimposition on the intermediate transfer belt, and secondary transfer collectively from the intermediate transfer belt to the recording paper.

In the above intermediate transfer system, a good image can be obtained if the transfer conditions are managed. Recently, the intermediate transfer system is more widely used in machines than the paper transport system.
When paying attention to the exposure means, there is an exposure apparatus corresponding to each image forming station or an exposure apparatus common to each image forming station. When an exposure apparatus is provided for each image forming station, the structure of each writing unit becomes simple with a full-color apparatus, but four writing units are required, and the cost is high. Become.

  On the other hand, a full-color image forming apparatus using two writing units in common, and an exposure apparatus common to each image forming station, optical element groups are arranged on both sides of the optical polarizer, and a photoconductor An image forming apparatus is disclosed in which the incident angles of the beams to the drum are all substantially equal (for example, Patent Documents 1 and 2).

  The exposure unit includes a plurality of image carriers arranged in parallel along the transfer paper, and an exposure unit that deflects and scans each image carrier with a laser beam modulated by an image signal to form a latent image. A laser beam is deflected and scanned with respect to each image carrier at an incident angle larger than 0 from the charging side, has a non-parallel optical path, and a plurality of signals modulated by image signals corresponding to each image carrier. An image forming apparatus having a laser light source, a rotating polygon mirror common to each laser light source, and an optical path that deflects and scans radially from a common reflecting surface of the rotating polygon mirror is disclosed (for example, Patent Document 3). The optical path lengths from the common reflecting surface of the rotary polygon mirror of this image forming apparatus to each image carrier are substantially the same, and the plurality of image carriers are transferred to the transfer medium from below along a diagonally arcuate line. It is arranged in parallel at the position where it comes into pressure contact.

Japanese Patent Laid-Open No. 10-221617 JP 2002-196271 A JP 2003-162122 A

However, in Patent Documents 1 and 2, since two writing units are required, the cost is high, and a larger space is required to be integrated. Further, positioning with respect to the image carrier is performed by each writing unit. There is a problem of having to.
Therefore, in recent years, many image forming apparatuses in which a single writing unit is combined or a writing unit is provided for each photosensitive unit are manufactured.

  However, if the writing unit is used in common, the diameter of the image carrier changes due to a design change or the distance from the polygon mirror to the photosensitive drum changes due to a change in the imaging optical system, etc. If the incident angle is constant, the change cannot be dealt with, and there is a risk that the beam may be blocked by the developing device or other devices that perform the electrophotographic process, or the beam may not reach the image carrier.

  Conversely, when a new writing unit is developed by commonly using each device that executes the conventional electrophotographic process, the distance from the light source to the image carrier cannot be changed so that the conventional device cannot be accommodated. There is also a problem that each device for executing the process must be newly designed.

  On the other hand, Patent Document 3 describes that deflection scanning is performed with an optical path having an incident angle larger than 0 from the charging side, and that the incident optical path is non-parallel. However, Patent Document 2 also points out. In addition, since it becomes difficult to make common the apparatus for executing the electrophotographic process around the image carrier of each station and to make it the same arrangement, particularly on the charging device and the developing device, it is difficult on the space. There is a problem that the restriction becomes large.

  Further, the diameter of the beam on the image carrier in the sub-scanning direction is not uniform, the color is uneven on the image, or the flare light of the beam reflected by the image carrier is applied to the cartridge case or the like. There is also a possibility that a problem of reflecting and appearing again at various positions on the image carrier may occur.

  Accordingly, an object of the present invention is not only to be able to use a common charging device and developing device, such as a charging device and a developing device, at each station distributed on both sides of the optical polarizer, but also to a writing unit and an electrophotographic process. Even if the apparatus that executes the above is changed, the size of the image forming apparatus may be kept as it is, the beam diameter is not uneven, the flare light countermeasure can be easily taken, and the optical scanning apparatus with improved image quality is provided. It is to provide.

According to the first aspect of the present invention, images are formed on a plurality of image carriers D _{k (k = 1 to n)} (n is a natural number) arranged in a line at a pitch of approximately 2i times the circumference (i is a natural number). A deflector that deflects and scans a plurality of laser beams modulated by a signal and has an imaging optical system arranged substantially symmetrically,
The deflected by the deflector plurality of laser beams _{LB k (k = 1~n) (} n is a natural number) irradiation point LP k on the plurality of image bearing members D _k a _{(k = 1 to n)} ( In an optical scanning device that forms a latent image by irradiating n to a natural number)
A normal HL _{k (k = 1 to n)} (n is a natural number) of the irradiation point LP _k and a reference point P _{k (k = 1 to n)} (n is a natural number) provided on the image carrier D _k. When the angle formed by the normal line AL _{k (k = 1 to n)} (n is a natural number) is α _{k (k = 1 to n)} (n is a natural number),
α _k are all the same value,
When the angle formed with the normal line HL _k when the laser beam LB _k irradiates the irradiation point LP _k is β _{k (k = 1 to n)} (n is a natural number),
β _k = ± 2 to 10 degrees and β ₁ × (−1) =... = β _j × (−1) = β _{j + 1} =... = β _n (j is 1 <j < n is a natural number).

According to the invention of claim 1, the normal line HL _{k (k = 1 to n)} (n is a natural number) of the irradiation point LP _k and the reference point P _{k (k = 1 to n)} provided on the image carrier D _{k . n) When} α _{k (k = 1 to n)} (n is a natural number) is an angle formed with the normal AL _{k (n = 1 to n)} (n is a natural number) of _n (n is a natural number), α _k is It is all the same value, and when the laser beam LB _k is the angle between the normal line HL _k when irradiated in the irradiation point _{LP k β k (k = 1~n} ) (n is a natural number), beta _k = ± 2 to 10 degrees and β ₁ × (−1) =... = Β _j × (−1) = β _{j + 1} =... = Β _n (j is 1 <j <n Therefore, in each image carrier D _k , the distance from the reference point P _k such as the transfer point, the charging point, and the development point to the irradiation point LP _k that is the writing position is constant, and there is no color misregistration. It is possible to obtain a simple image. In addition, even if the station pitch of the process cartridge is changed slightly, the design freedom increases even if the writing unit is changed slightly, so that it can be used as it was in the previous process conditions. It is possible to reduce the size of the apparatus without changing other conditions. In addition, since limiting the incident angle to the two, the diameter of the laser beam at the irradiation point LP _k on the image carrier stably even a two, variation in the diameter of the laser beam becomes possible suppression.

According to the second aspect of the present invention, an image is formed on a plurality of image carriers D _{k (k = 1 to n)} (n is a natural number) arranged in a line at a pitch of approximately 2i times the circumference (i is a natural number). A plurality of laser beams modulated by the signal are deflected and scanned, and a polarizing device having an imaging optical system arranged substantially symmetrically is provided, and the plurality of laser beams LB _{k (k = 1˜)} deflected by the deflecting device are provided _{. n) In} the optical scanning device that forms a latent image by irradiating (n is a natural number) to irradiation points LP _{k (k = 1 to n)} (n is a natural number) on the plurality of image carriers D _k , The normal of the point LP _k HL _{k (k = 1 to n)} (n is a natural number) and the reference point P _{k (k = 1 to n)} (n is a natural number) provided on the image carrier D _k When the angle between the line AL _{k (k = 1 to n)} (n is a natural number) is α _{k (k = 1 to n)} (n is a natural number), all α _k have the same value, and the laser beam LB _k is the irradiation point When the angle formed between the normal line HL _k when irradiating the _{P k β k (k = 1~n} ) (n is a natural number), a beta _k = ± 2 to 10 degrees, and beta _k is All have the same value.

According to the invention of claim 2, the normal line HL _{k (k = 1 to n)} (n is a natural number) of the irradiation point LP _k and the reference point P _{k (k = 1 to n)} provided on the image carrier D _{k . n) When} α _{k (k = 1 to n)} (n is a natural number) is an angle formed with the normal AL _{k (n = 1 to n)} (n is a natural number) of _n (n is a natural number), α _k is It is all the same value, and when the laser beam LB _k is the angle between the normal line HL _k when irradiated in the irradiation point _{LP k β k (k = 1~n} ) (n is a natural number), beta _k = ± 2 to 10 degrees and β _k is the same value, so the diameter of the laser beam at the irradiation point LP _k on the image carrier D _k is also the same, and the variation in the diameter of the laser beam can be further suppressed. It becomes.

  According to a third aspect of the present invention, there is provided an image forming apparatus comprising the optical scanning device according to the first or second aspect.

According to the first aspect of the present invention, the normal HL _{k (k = 1 to n)} (n is a natural number) of the irradiation point LP _k and the reference point P _{k (k = k =} ) provided on the image carrier D _{k. 1 to n)} (where n is to be normal AL k is a natural _{number) (k =} 1~n) _(n is the angle _{α k (k = 1~n) (} n is a natural number is a natural number)), alpha _{When k} is all the same value and β _{k (k = 1 to n)} (n is a natural number) is an angle between the laser beam LB _k and the normal HL _k when the irradiation point LP _k is irradiated, β _k = ± 2 to 10 degrees and β ₁ × (−1) =... β _j × (−1) = β _{j + 1} ... = β _n (j is 1 <j <n Therefore, in each image carrier D _k , the distance from the reference point P _k such as the transfer point, the charging point, and the development point to the irradiation point LP _k that is the writing position is constant, and there is no color misregistration. Can be obtained.

In addition, even if the station pitch of the process cartridge is changed slightly, the design freedom increases even if the writing unit is changed slightly, so that it can be used as it was in the previous process conditions. The size of the apparatus can be reduced without changing other conditions.
In addition, since limiting the incident angle to the two, the diameter of the laser beam at the irradiation point LP _k on the image carrier stably even a two, bi - smoothing out fluctuations beam diameter, the abnormal image Occurrence can be prevented.

According to the second aspect of the present invention, the normal HL _{k (k = 1 to n)} (n is a natural number) of the irradiation point LP _k and the reference point P _{k (k = k =} ) provided on the image carrier D _{k. 1 to n)} (where n is to be normal AL k is a natural _{number) (k =} 1~n) _(n is the angle _{α k (k = 1~n) (} n is a natural number is a natural number)), alpha _{When k} is all the same value and β _{k (k = 1 to n)} (n is a natural number) is an angle between the laser beam LB _k and the normal HL _k when the irradiation point LP _k is irradiated, Since β _k = ± 2 to 10 degrees and β _k are all the same value, the diameters of the laser beams at the irradiation point LP _k on the image carrier D _k can be reliably made the same, and the laser The variation in the beam diameter can be further suppressed, and the occurrence of abnormal images can be further prevented.

  According to the third aspect of the present invention, it is possible to provide an image forming apparatus including an optical scanning device that exhibits any of the above effects. Further, even if the station pitch is slightly changed, the conventional imaging optical system can be used, and an image forming apparatus that obtains a good image can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing a color printer as an image forming apparatus provided with an optical scanning device according to an embodiment of the present invention.

First, a schematic configuration of the color printer CP will be described.
A color printer CP shown in FIG. 1 is a four-drum full-color type electrophotographic image forming apparatus, and a photosensitive drum (image carrier) D ₁ , D ₂ , D having a diameter of 40 mm is contained in the apparatus main body 1. ₃ , _four photosensitive units 2 A, 2 B, 2 C, 2 D having D ₄ are provided at regular intervals so as to be detachable from the apparatus main body 1. The photoreceptor units 2A to 2D are provided with a charging device 14, a cleaning device, and the like. In this example, four photosensitive drums are provided, but the present invention is not limited to this.

In the color printer CP, a transfer belt 3 for transferring an image onto a sheet P is wound around a plurality of rollers at approximately the center in the apparatus main body 1 and is stretched so as to be rotatable in an arrow A direction. The diameters of the photosensitive drums D _{1 to} D ₄ are not limited to 40 mm.

The photoreceptor units 2A to 2D are disposed on the upper surface of the transfer belt 3 so that the photoreceptor drums 5A to 5D provided in the four photoreceptor units 2A to 2D are in contact with each other. That is, the photosensitive drums D _{1 to} D ₄ are arranged in a line at a constant interval (pitch) that is approximately twice the circumference.
Specifically, as shown in FIG. 2, unified to each of the photosensitive drums D ₁ the distance d to D ₄ corresponding to approximately twice the circumferential length of the photosensitive drum D ₁ to D ₄ having a diameter of 40 mm 251.33Mm To do. The photosensitive drums D _{1 to} D ₄ are driven to rotate clockwise by a motor that is driven to rotate via a drum drive timing belt and a drum drive pulley (not shown).

In this example, the photosensitive drums D _{1 to} D ₄ are arranged in a line at a pitch that is approximately twice the circumference thereof, but the present invention is not limited to this, and the photosensitive drums D _{1 to} D are not limited thereto. They may be arranged in a line at a pitch of approximately 2i times the circumference of ₄ (i is a natural number).
Then, developing devices 10A, 10B, 10C, and 10D corresponding to the respective photoreceptor units 2A to 2D are provided. The developing devices 10A to 10D are provided with toners used as developers having different colors.

  Further, an optical scanning device 6 is provided above each of the photoreceptor units 2 </ b> A to 2 </ b> D, and a duplex unit 7 is provided below the transfer belt 3. Further, the color printer CP is equipped with a reversing unit 8 on the left side of the apparatus main body 1 for reversing and discharging the transfer paper P after image formation or transporting it to the duplex unit 7.

  Between the transfer belt 3 and the reversing unit 8, there is provided a fixing device 9 for fixing the image of the transfer paper onto which the image has been transferred. A reversal conveyance path 20 is formed on the downstream side of the fixing device 9 in the transfer sheet conveyance direction, and the transfer sheet P conveyed there can be discharged onto the discharge tray 26 by the discharge roller pair 25. .

  In the lower part of the apparatus main body 1, there are provided paper feed cassettes 11 and 12 that can store transfer papers P having different sizes, for example, in two upper and lower stages. Further, a manual feed tray 13 is provided on the right side surface of the apparatus main body 1 so as to be openable and closable in the direction of arrow B. By opening the manual feed tray 13, the transfer paper P is manually fed therefrom.

  In this example, the photoconductor units 2A to 2D all use units having the same configuration, the photoconductor unit 2A forms an image corresponding to yellow, and the photoconductor unit 2B forms an image corresponding to magenta. The photoconductor unit 2C forms an image corresponding to cyan, and the photoconductor unit 2D forms an image corresponding to black. Note that the colors of the images formed by the photoreceptor units 2A to 2D are not limited to this example.

Next, the outline of the operation of the color printer CP will be described with reference to FIG.
The color printer CP is connected to a personal computer (not shown) or the like, and upon receiving a print request from the personal computer or the like, the control unit causes each device to start an image forming operation. Then, each of the photosensitive drums D _{1 to} D ₄ rotates clockwise. The surfaces of the photosensitive drums D _{1 to} D ₄ are uniformly charged by the charging roller 14 of each charging device. Then, the surface of each of the photosensitive drums D _{1 to} D ₄ is irradiated with a laser beam corresponding to the image of each color by the optical scanning device 6 to form an electrostatic latent image. Then, the electrostatic latent images on the photosensitive drums D _{1 to} D ₄ are developed by the toners of the respective colors by the developing devices 10A to 10D to form four-color toner images.

On the other hand, the paper P is fed from the selected one of the paper feeding cassettes 11 and 12 by the separation paper feeding sections 55 and 56, and is temporarily stopped by the registration roller pair 59 provided immediately before the photosensitive unit 2A. Thereafter, the sheet is conveyed between the photosensitive drum D ₁ of the photosensitive unit 2A and the transfer belt 3 at an accurate timing that coincides with the toner image formed on each photosensitive drum D _1. .

  At that time, the paper P is charged to a positive polarity by a paper suction roller 58 disposed in the vicinity of the entrance of the transfer belt 3, and thereby electrostatically attracted to the surface of the transfer belt 3. Then, the sheet P is conveyed in accordance with the rotation of the transfer belt 3 in the direction of arrow A while being attracted to the transfer belt 3, and the toner images of the respective colors are sequentially transferred onto the upper surface. Then, when passing through the photoreceptor unit 2D, a full color toner image in which four colors are superimposed is formed.

  Heat and pressure are applied to the paper P on which the toner image is formed by the fixing device 9, and the toner image is melted and fixed on the paper p. Thereafter, the paper is reversed and discharged to the paper discharge tray 26 at the top of the apparatus main body 1 in the designated carry-out mode, or is straightly moved from the fixing device 9 and discharged from the reversing unit 8 to the straight line.

On the other hand, when the double-sided image forming mode is selected, the sheet is sent to the reversing conveyance path 54 in the reversing unit 8 described above, then switched back and conveyed to the double-sided unit 7, and is re-fed from there to be photosensitive. After the toner image is formed on the back surface of the paper P in the image forming unit in which the body units 2A to 2D are provided, the toner image is discharged in any of the above-described discharge modes.
Note that when the image formation is instructed for a plurality of documents, or when the output of a plurality of documents is instructed for one document, the above-described process is repeated.

As shown in FIG. 2, the optical scanning device 6 of this example emits from laser light sources corresponding to four (plural) laser beams, yellow, cyan, magenta, and black modulated from image signals. The four types of laser beams LB ₁ , LB ₂ , LB ₃ , and LB ₄ are deflected by the optical polarizer 31 in which the imaging optical system is arranged substantially symmetrically with respect to the center line CL of the optical deflector 31. By means of a plurality of optical element groups 32 to 35 having mirrors corresponding to the respective beams, laser beams corresponding to the image signals of the respective colors are irradiated on the photosensitive drums D _{1 to} D _{4 at} the irradiation points LP ₁ , LP ₂ , The latent image is formed by irradiating LP ₃ and LP ₄ .
In this example, four types of photosensitive drums and four laser beams are provided, but the present invention is not limited to this, and a plurality of photosensitive drums and laser beams may be provided.

In this optical scanning device 6, the optical element groups 32 and 33 and the optical element groups 34 and 35 are arranged separately on both sides around the optical polarizer 31, and the optical element groups 32, 33, 34, The laser beams incident on the photosensitive drums D _{1 to} D ₄ from the 35 folding mirrors 41, 42, 43, and 44 are set as follows.

That is, as shown in FIG. 3, the normal HL ₁ of the irradiation point _{LP 1 ~LP 4, HL 2,} HL 3, HL 4 and, criteria such as provided on the photosensitive drum D ₁ to D ₄ for example charging points When the angles formed by the normals AL ₁ , AL ₂ , AL ₃ and AL ₄ of the points P ₁ , P ₂ , P ₃ and P ₄ are α ₁ , α ₂ , α ₃ and α ₄ , α _{1 to} α ₄ is the same value for all and ₁ the angle between the normal HL ₁ ～HL ₄ when the laser beam LB ₁ ～LB ₄ is irradiated to the irradiation point _{LP 1 ~LP 4 β, β 2} , β 3, When β ₄ , β _{1 to} β ₄ = ± 2 to 10 degrees, and β ₁ × (−1) = β ₂ × (−1) = β ₃ = β ₄ is satisfied.

That is, (β ₁ , β ₂ ) and (β ₃ , β ₄ ) facing each other across the center line CL of the optical polarizer 31 are symmetric with respect to the normal lines HL _{1 to} HL ₄ from the direction of the laser beam LB. _{1 to} LB ₄ are incident.
At this time, the optical path lengths from the polygon mirrors 38 and 39 to the points reaching the photosensitive drums D _{1 to} D ₄ are set to be the same.

Further, the reference points P _{1 to} P ₄ are set at the vertices on the photosensitive drums D _{1 to} D ₄ , and the angle can be easily measured by matching with the charging point, the developing point, the transfer point, and the like.
In addition, β ₁ to β ₄ are β ₁ = β ₂ so that the reflected light (returned light) from the casings of the photosensitive drums D _{1 to} D ₄ (not shown) does not affect the laser beam power adjustment. = −2 to 10 degrees and β ₃ = β ₄ = + 2 to 10 degrees. That is, β _{k (k = 1 to n)} (n is a natural number) = ± 2 to 10 degrees, and β ₁ × (−1) =... = Β _j × (−1) = β _{j + 1} =... = Β _n (j is a natural number where 1 <j <n).

Therefore, the laser beam LB ₁ ~LB ₄ irradiates an irradiation point LP ₁ ~LP ₄ in the predetermined angle from the reference point P ₁ to P _4, and the normal HL ₁ ~HL irradiation point LP ₁ ~LP _{4 4 is} incident at two different incident angle optical paths within a certain range (+2 to 10 degrees, −2 to 10 degrees). In addition, when β _{1 to} β ₄ are all the same value, it is more effective.

In addition, an angle is selected so that the reflected light of the laser light from each of the photosensitive drums D _{1 to} D ₄ does not reach the photosensitive drum again, or a light shielding member is provided. Setting by reducing the inclination with respect to the incident light makes it possible to reduce the opening width until reaching the photosensitive drums D _{1 to} D _4, and it is not necessary to consider the influence of the reflected flare light.

  The optical scanning device 6 includes an optical polarizer 31 in the approximate center of the optical housing 36. The optical polarizer 31 is capable of rotating two upper and lower polygon mirrors 38 and 39 around the rotation axis of the polygon motor 37, respectively. It is attached. Further, in the optical housing 36, as described above, the optical system element groups 32 and 35 and the optical system element groups 33 and 34 are arranged so as to be distributed to the left and right with the optical polarizer 31 as the center. The optical element group 32 includes a two-layer fθ lens (imaging lens) 45, an imaging lens 46, and folding mirrors 41, 81, and 82. The optical element group 33 includes a two-layer fθ lens (imaging lens) 45 and the like. The optical element group 34 includes a two-layer fθ lens (imaging lens) 65, an imaging lens 67, and folding mirrors 43, 62, and 66, and the imaging lens 49 and the folding mirrors 42, 47, and 83. The optical element group 35 includes a two-layer fθ lens (imaging lens) 65, an imaging lens 68, and folding mirrors 44, 84, and 85.

Then, the optical element group 32, yellow - leads to beam on the surface of the photosensitive drum D _1, the optical element group 33 is bi corresponds to the magenta color image - - bi corresponding to the color of the image beam photoreceptor lead on the surface of the drum D _2. Further, the optical element group 34 is bi correspond to the cyan image - leads to beam on the surface of the photosensitive drum D _3, the optical element group 35 corresponds to the black color of the image bi - photoreceptor drum beam D Lead to ₄ surfaces.

As described above, the optical scanning device 6 has four stations that emit beams corresponding to yellow, magenta, cyan, and black images, and is a four-drum tandem type writing optical system. Is configured. The interval d between the stations is approximately 2n times the diameter of the photosensitive drums D _{1 to} D ₄ (n is a natural number), preferably approximately 2 or 4 times the diameter of the photosensitive drums D _{1 to} D _4. To be. A dustproof glass 16 for dustproofing is attached to the exit of each beam to the photoreceptor units 2A to 2D formed in the optical housing 36, respectively.

1 is a schematic cross-sectional view of a color printer including an optical scanning device as an example of an image forming apparatus of the present invention. It is a schematic sectional drawing which shows an example of the optical scanning device with which the image forming apparatus shown in FIG. 1 is equipped. FIG. 3 is a diagram for explaining a relationship between a beam emitted from the optical scanning device shown in FIG. 2 and a photosensitive drum irradiated with the beam.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus main body 2A, 2B, 2C, 2D Photosensitive unit 3 Transfer belt 6 Optical scanning device 7 Duplex unit 8 Reversing unit 9 Fixing device 10A, 10B, 10C, 10D Developing device 11, 12 Paper feed cassette 13 Manual tray 14 Charging device 16 Dust-proof glass 20 Reverse conveyance path 25 Discharge roller pair 26 Discharge tray 31 Optical deflector 32, 33, 34, 35 Optical element group 36 Optical housing 37 Polygon motor 38, 39 Polygon mirror 41, 42, 43, 44, 47, 62, 66, 81, 82, 83, 84, 85 Folding mirror 45, 65 fθ lens (imaging lens)
46,49,67,68 imaging lens 55 and 56 separating feeding unit 58 the paper attracting roller 59 pair of registration rollers _{AL 1, AL 2, AL 3} , AL 4, HL 1, HL 2, HL 3, HL 4 normal CL center line CP color printer (image forming device)
D ₁ , D ₂ , D ₃ , D ₄ photosensitive drum (image carrier)
d Interval (Pitch)
LB ₁ , LB ₂ , LB ₃ , LB ₄ laser beam LP ₁ , LP ₂ , LP ₃ , LP ₄ irradiation point P ₁ , P ₂ , P ₃ , P ₄ reference point P paper α ₁ , α ₂ , α ₃ , α ₄ , β ₁ , β ₂ , β ₃ , β ₄ angles

Claims (3)

A plurality of laser beams modulated by image signals on a plurality of image carriers D _{k (k = 1 to n)} (n is a natural number) arranged in a line at a pitch of approximately 2i times the circumference (i is a natural number) Is provided with a polarizer in which the imaging optical system is arranged substantially symmetrically.
The deflected by the deflector plurality of laser beams _{LB k (k = 1~n) (} n is a natural number) irradiation point LP k on the plurality of image bearing members D _k a _{(k = 1 to n)} ( In an optical scanning device that forms a latent image by irradiating n to a natural number)
A normal HL _{k (k = 1 to n)} (n is a natural number) of the irradiation point LP _k and a reference point P _{k (k = 1 to n)} (n is a natural number) provided on the image carrier D _k. When the angle formed by the normal line AL _{k (k = 1 to n)} (n is a natural number) is α _{k (k = 1 to n)} (n is a natural number),
α _k are all the same value,
When the angle formed with the normal line HL _k when the laser beam LB _k irradiates the irradiation point LP _k is β _{k (k = 1 to n)} (n is a natural number),
β _k = ± 2 to 10 degrees and β ₁ × (−1) =... = β _j × (−1) = β _{j + 1} =... = β _n (j is 1 <j < n is a natural number). A plurality of laser beams modulated by image signals on a plurality of image carriers D _{k (k = 1 to n)} (n is a natural number) arranged in a line at a pitch of approximately 2i times the circumference (i is a natural number) Is provided with a polarizer in which the imaging optical system is arranged substantially symmetrically.
The deflected by the deflector plurality of laser beams _{LB k (k = 1~n) (} n is a natural number) irradiation point LP k on the plurality of image bearing members D _k a _{(k = 1 to n)} ( In an optical scanning device that forms a latent image by irradiating n to a natural number)
A normal HL _{k (k = 1 to n)} (n is a natural number) of the irradiation point LP _k and a reference point P _{k (k = 1 to n)} (n is a natural number) provided on the image carrier D _k. When the angle formed by the normal line AL _{k (k = 1 to n)} (n is a natural number) is α _{k (k = 1 to n)} (n is a natural number),
α _k are all the same value,
When the angle formed with the normal line HL _k when the laser beam LB _k irradiates the irradiation point LP _k is β _{k (k = 1 to n)} (n is a natural number),
β _k = ± 2 to 10 degrees, and β _k is the same value. An image forming apparatus comprising the optical scanning device according to claim 1.

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