JP2002067384A - Image forming device - Google Patents

Abstract

(57) [Problem] To improve a process speed in an image forming apparatus without deteriorating image quality such as color misregistration. SOLUTION: Four charged photosensitive drums 18a and 18 after charging are provided.
b, 18c, and 18d, respectively, with the laser scanner 1
Scanning is performed with laser beams a, b, c, and d by 1a, 11b, 11c, and 11d to form an electrostatic latent image. Each laser beam is composed of two laser beams,
The intervals Δa, Δb, Δc, Δd are set to be the same. As described above, since the electrostatic latent image is formed by the two laser beams, the process speed can be increased without increasing the rotation speed of the polygon mirror. As a result, the process speed can be increased without deteriorating the image quality such as color misregistration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer, and more particularly, to an electrophotographic image forming apparatus having a plurality of laser scanners and a photosensitive member.

[0002]

2. Description of the Related Art In an electrophotographic color image forming apparatus (for example, a copying machine or a laser printer), four color toners of yellow (Y), magenta (M), cyan (C) and black (Bk) are used. By superimposing the images,
Four full-color images are formed. Various methods have been devised and commercialized for such an electrophotographic image forming apparatus.

For example, using one photosensitive drum, toner images of different colors are sequentially formed on the photosensitive drum, and these toner images are sequentially placed on an intermediate transfer member (an intermediate transfer drum or an intermediate transfer belt). There is a method of transferring and superimposing a toner image.

On the other hand, there is another type in which a toner image is superposed on a photosensitive drum without using an intermediate transfer member. According to this method, the cost can be reduced by the amount by which the intermediate transfer member is unnecessary. However, it is necessary to re-expose from the toner image previously formed on the photosensitive drum, and the image has a disadvantage that it is inferior to the method using the above-described intermediate transfer member. It seems that the one using an intermediate transfer member will be the mainstream.

[0005] The image forming speed (print speed) of a four-color full-color image forming apparatus using the above-mentioned intermediate transfer member is mainly about 4 to 6 sheets per minute.
Further speed-up is desired in the future. However, as described above, in a method in which toner images are formed one by one on one photosensitive drum, toner images of each color cannot be formed in parallel, so that the process speed is increased. Even so, the limit is about 10 to 12 sheets per minute.

In such a background, a four-drum type (tandem type) color image forming apparatus equipped with four image forming units (image forming stations) for forming toner images of respective colors has been commercialized. I have. Some of the tandem-type image forming apparatuses use not only a laser beam as an exposure unit but also an LED. In the tandem type color image forming apparatus, since the conveying speed of a recording material such as paper is the same as the process speed, it is considered that the speed will be increased in the future.

[0007]

However, according to the above conventional example, there are the following disadvantages.

In order to increase the process speed, it is necessary to increase the transport speed and the scanning means. This transport speed can be technically possible by increasing the number of rotations of the motor constituting the drive system, but the scanning means has technical difficulties. For example, in the case of a 600 dpi image forming apparatus using a four-sided polygon mirror, the scanner motor, which is one of the main components of the scanning means, is calculated to be about 40,000 rpm when the process speed is 24 sheets per minute. Is technically difficult at present.

In order to reduce the number of rotations of the polygon mirror, it is conceivable to increase the number of surfaces of the polygon mirror. However, if the number of surfaces is increased, the scanning width becomes narrower. The optical path length to the photosensitive drum surface becomes long. In a color image forming apparatus in which color misregistration of four colors is regarded as important, if the optical path length is increased, color misregistration is likely to occur, resulting in deterioration of image quality.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an image forming apparatus capable of increasing the process speed without deteriorating image quality such as color misregistration. It is assumed that.

[0011]

According to the first aspect of the present invention, there is provided an image carrier, and an electrostatic latent image is formed by scanning the surface of the image carrier after charging. In the image forming apparatus provided with an exposure unit, the exposure unit is a laser oscillation unit that generates a plurality of laser beams individually modulated based on image signals, and a plurality of laser beams generated from the laser oscillation unit Multi-beam scanning means for scanning the surface of the image carrier with a laser beam, wherein the multi-beam scanning means simultaneously moves the plurality of laser beams in the scanning direction at different positions in the sub-scanning direction. The width of the portion irradiated by the plurality of laser beams in the sub-scanning direction is the same for the plurality of exposure units. It is characterized in.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a plurality of the image carriers and at least one of the exposing means arranged to face each of the image carriers are provided. It is characterized by having.

According to a third aspect of the present invention, there is provided the image forming apparatus according to the first aspect, further comprising a plurality of the exposing means arranged to face one image carrier. .

The present invention according to claim 4 is based on claims 1, 2,
In the image forming apparatus described in Item 3, the width of the portion of the exposure unit irradiated by the plurality of laser beams in the sub-scanning direction is the same as the resolution of the image carrier in the sub-scanning direction. , Characterized in that.

The present invention according to claim 5 is based on claims 1, 2,
In the image forming apparatus described in Item 3, the width of the portion of the exposure unit irradiated by the plurality of laser beams in the sub-scanning direction is an odd multiple of the resolution of the image carrier in the sub-scanning direction. There is a feature.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
This is a four-drum type full-color image forming apparatus, and FIG. 1 is a longitudinal sectional view showing a schematic configuration thereof.

The image forming apparatus shown in FIG. 1 includes four image forming stations Sa, Sb, Sc, and Sd.
These image forming stations Sa, Sb, Sc, Sd
Are used to form black (Bk), cyan (C), magenta (M), and yellow (Y) toner images in this order. The moving direction of the transfer belt 20 as a recording material carrier (in the direction of arrow R20) ) Are arranged in order from the upstream side.

Image forming stations Sa, Sb, Sc,
Sd denotes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) 18a, 18b, 18 as an image carrier.
c, 18d. These photosensitive drums 18a, 1
A charging roller (primary charging device) is provided around the periphery of each of the charging rollers 8b, 18c, and 18d substantially in the rotation direction (the direction of the arrow).
16a, 16b, 16c, 16d, scanner units (exposure means) 11a, 11b, 11c, 11d, developing devices 14a, 14b, 14c, 14d, transfer rollers (transfer charging devices) 19a, 19b, 19c, 19d, cleaning blades ( Cleaning member) 15a, 15b, 1
5c and 15d are provided.

The above-mentioned charging rollers 16a, 16b, 16
c, 16d and cleaning blades 15a, 15
b, 15c, 15d are cleaners 12a, 12b, 12
c, 12d are integrally incorporated.

The above-mentioned developing devices 14a, 14b, 14c,
14d is a photosensitive drum 18a, 18b, 18c, 18d
Developing rollers 17a, 17b, 17c, and 1 for attaching toner to the electrostatic latent image formed thereon and developing the toner image.
7d.

The above-described transfer belt 20 includes a driving roller 20
b and the driven roller 20a, and is configured to rotate (move) in the direction of the arrow 20 with the rotation of the drive roller 20b in the direction of the arrow. Further, below the transfer belt 20, a paper feed cassette 22 for storing a recording material P such as paper is provided. Paper cassette 2 in FIG.
2, a paper feed roller 25 is provided, and a paper feed sensor 24 and a registration roller 21 are provided upstream of the transfer belt 20 in the supply direction of the recording material P. Have been. Further, a fixing device 23 is provided on the downstream side of the transfer belt 20 along the conveying direction of the recording material P.

The operation of the image forming apparatus having the above configuration is as follows.

Each photosensitive drum 18a, 18b, 18c, 1
8d is rotationally driven in the direction of the arrow by a driving means (not shown), and the respective surfaces thereof are charged rollers 16a, 16b,
By 16c and 16d, it is uniformly charged to a predetermined polarity and potential. Charged photosensitive drums 18a, 18b, 18
c and 18d are the scanner units 11 according to the image information.
The laser beams a, b, c, and d scanned by the laser beams a, 11b, 11c, and 11d are irradiated, and the charges on the irradiated portions are removed to form an electrostatic latent image.

Thus, each of the photosensitive drums 18a, 18b, 1
The electrostatic latent images formed on 8c and 18d are
a, 14b, 14c, 14d of developing rollers 17a, 17
The toners of the respective colors are adhered by b, 17c and 17d, and are developed as toner images.

The toner images of each color are sequentially transferred onto a recording material P carried on the surface of the transfer belt 20. The recording material P stored in the paper supply cassette 22 is supplied by the paper supply roller 25, temporarily stopped by the registration roller 21, and thereafter, the photosensitive drums 18a, 18
The toner image is supplied from the registration roller 21 to the transfer belt 20 at the same timing as the toner images on b, 18c, and 18d, and is carried on the transfer belt 20. Thus, the recording material P carried on the transfer belt 20 is rotated by the rotation of the transfer belt 20 in the direction of the arrow R20 along with the rotation of the drive roller 20b in the direction of the arrow, so that each image forming station S
The toner images on the photosensitive drums 18a, 18b, 18c, and 18d are sequentially transferred to a, Sb, Sc, and Sd, respectively, and are sequentially transferred. As a result, the four color toner images are superimposed on the recording material P.

Recording material P on which transfer of four color toner images has been completed
Is separated from the transfer belt 20, heated and pressed by the fixing device 23 to fix the toner image on the surface, and then discharged outside the image forming apparatus main body.

On the other hand, the toner (residual toner) remaining on the photosensitive drums 18a, 18b, 18c and 18d without being transferred onto the recording material P is transferred to each of the cleaning devices 12a and 12d.
b, 12c, 12d cleaning blades 15a, 1
It is removed by 5b, 15c, and 15d and used for the next image formation.

Each of the above scanner units 11a, 11
b, 11c and 11d denote laser oscillation means (not shown) such as a multi-beam laser diode for generating a plurality of laser beams individually modulated based on image signals.
And the photosensitive drums 18a, 18b, 18c, 1 by the plurality of laser beams generated from the laser oscillation means.
And a multi-beam scanning means (not shown) such as a polygon mirror for scanning the 8d surface. The multi-beam scanning means simultaneously moves a plurality of laser beams in the scanning direction at different positions in the sub-scanning direction. It is configured as follows.

In the present embodiment, the scanner unit 11
As shown in FIG. 2 which is a perspective view, a, 11b, 11c, and 11d denote charged photosensitive drums 18a, 18b, and 18d.
Two laser beams are respectively applied to c and 18d.

For example, two laser beams a emitted from the laser scanner 11a irradiate substantially different positions in the circumferential direction (rotation direction) of the surface of the photosensitive drum 18a almost simultaneously.
Each is scanned along the generatrix. Two laser beams a
When the extended lines in the scanning direction are denoted by a1 and a2, the difference Δa between them is approximately the interval between the two laser beams a.
In practice, the interval between the two laser beams is a distance along the circumferential direction of the photosensitive drum, but since this distance is minute compared to the radius of the photosensitive drum, the distance between a1 and a2 is small. The distance between the two laser beams is defined as a linear distance. Other laser scanners 11b, 11c, 11d
Is similar to that of the laser scanner 11a described above.
That is, the intervals (widths along the sub-scanning direction) between the two laser beams b, c, and d of the laser scanners 11b, 11c, and 11d are Δb, Δc, and Δd in this order. These intervals Δa, Δb, Δc, and Δd are all set to be equal.

FIG. 3 is a diagram for explaining the interval between laser beams for scanning the photosensitive drum surface. In the figure,
Laser beams with the same numbers are laser beams that simultaneously scan the surface of the photosensitive drum. For example, the laser beam 41a and the laser beam 41b are laser beams that are simultaneously scanned by one surface of a polygon mirror (not shown), and the laser beam 42a and the laser beam 42
b is a laser beam that is simultaneously scanned by the next surface of the polygon mirror. Hereinafter, the laser beam 48a,
The same applies to 48b. An interval 49 between two laser beams (for example, laser beams 41a and 41b) shown in FIG.
Is equal to the interval Δa shown in FIG. In the example shown in FIG.
The interval 49 is the resolution in the sub-scanning direction of the laser scanner, that is, the number of scanning lines per unit length (line / inc.
h).

Each of the two laser beams 41a and 41b scanned by the above-described laser scanners, for example, the laser scanner 11a, is independently controlled with respect to ON / OFF timing, light amount, and the like.

Therefore, according to the present embodiment, the surface of the photosensitive drum can be simultaneously scanned by two laser beams by each scanner unit, so that a scanner motor (not shown) for rotating the polygon mirror at high speed is provided.
With the number of revolutions set to the same as the conventional, practically,
The same effect as when the number of rotations is doubled can be obtained.

FIG. 4 shows another example of the interval between two laser beams. In this figure, as in FIG. 3, laser beams assigned the same numbers are laser beams that simultaneously scan the surface of the photosensitive drum. For example, the laser beam 52a and the laser beam 52b are laser beams that are simultaneously scanned by one surface of a polygon mirror (not shown), and the laser beam 53a and the laser beam 53b are scanned by the next surface of the polygon mirror. These are laser beams that are scanned simultaneously. In the example shown in FIG. 4, an interval 50 between two laser beams (for example, a laser beam 52a and a laser beam 52b) scanned by the same surface of the polygon mirror.
Is set to be three times (odd number) the resolution, and between these two laser beams 52a and 52b,
The other two laser beams 51b and 53a are scanned.
In this case, in the sub-scanning direction, the surface of the photosensitive drum can be scanned evenly by scanning at a pitch twice the resolution.

In this embodiment, the relative positions of the respective scanner units 11a, 11b, 11c, and 11d with respect to the respective photosensitive drums 18a, 18b, 18c, and 18d are the same. If the two laser beams emitted from each scanner unit are set to be at equal intervals when exiting from each scanner unit,
In a state where each photosensitive drum is irradiated, the interval between the two laser beams becomes equal.

As described above, the interval between two laser beams scanned by one scanner unit is
The resolution may be set equal to the resolution in the sub-scanning direction, or may be set to an integral multiple of the resolution.

<Second Embodiment> FIG. 5 shows a second embodiment. The image forming apparatus shown in FIG. 1 uses a large-diameter photosensitive drum as an image carrier, and a plurality of sets of process devices for forming a toner image on the photosensitive drum (in the example of FIG. Pairs) are arranged. The paper feeding unit and the fixing device for the recording material P are the same as those in the image forming apparatus of the first embodiment, and thus the description is omitted.

The photosensitive drum 61 as an image carrier has a large diameter, that is, a so-called large diameter, in order to secure a space for disposing four sets of process equipment around the photosensitive drum 61.

The rotation direction of the photosensitive drum 61 is set in the direction of arrow R61, and the primary charger (yellow) for the first color (yellow) is arranged in order from immediately downstream of the transfer roller (transfer charging device) 74 along the rotation direction. (Charging device) 62a, scanner unit (exposure means) 63a, and developing device 64a
Are arranged, then a primary charger (charging device) 62b for the second color (magenta), a scanner unit (exposure means) 63b, and a developing device 64b are also disposed, and then a third color (cyan) ) Primary charger (charging device) 6
2c, a scanner unit (exposure means) 63c and a developing device 64c are also arranged. Next, a primary charger (charging device) 62d for the fourth color (black), a scanner unit (exposure means) 63d, and Developing device 64
d is arranged.

The above-mentioned photosensitive drum 61 is driven to rotate in the direction of arrow R61 by a driving means (not shown), and a yellow toner image as a first color is first formed on the surface thereof. That is, the surface of the photosensitive drum 61 is
The laser beam is uniformly charged to a predetermined polarity and potential by 2a, and the charge of the irradiated portion is removed by two laser beams emitted from the scanner unit 63a to form an electrostatic latent image. The electrostatic latent image is developed as a yellow toner image by attaching toner to the developing device 64a. The same process is performed for magenta, cyan, and black, and four color toner images are superimposed on the surface of the photosensitive drum 61. The four color toner images on the photosensitive drum 61 are
The image is collectively transferred onto the surface of the recording material P supplied in the direction of the arrow Kp between the photosensitive drum 61 and the transfer roller 74.
The image is fixed by a fixing device (not shown).

Also in this embodiment, each of the above-mentioned scanner units 62a, 62b, 62c and 62d generates two laser beams. In the first embodiment described above, the two laser beams generated from each scanner unit are configured so that the intervals are the same when they exit the scanner unit. On the other hand, in the present embodiment, the photosensitive drum 6 is provided for each scanner unit.
Since the irradiation angle of the laser beam with respect to 1 is different, the interval between the two laser beams in the state where the surface of the photosensitive drum 61 is irradiated is set to be the same.
That is, the configuration is such that Δa, Δb, Δc, and Δd in FIG. 5 are the same.

Further, in this embodiment, in order to make the configuration of the image forming apparatus main body compact, each scanner unit is arranged so that the scanning surface of the laser beam is horizontal, and The length in the vertical direction is reduced.

It should be noted that the developing devices 64a, 64b, 64c, 64d and the scanner unit 6
It is also possible to radially dispose 3a, 63b, 63c, 63d. In this case, each scanner unit 63
The scanner units 63a, 63b, 63c, 63d are similar to the first embodiment.
By making the intervals between the two laser beams emitted from d equal, it is possible to make the intervals Δa, Δb, Δc, and Δd between the two laser beams irradiated on the surface of the photosensitive drum 61 equal.

<Embodiment 3> In Embodiments 1 and 2 described above, the number of laser beams emitted from one scanner unit is two. In No. 3, four laser beams are generated from one scanner unit.

As shown in FIG. 6, four laser beams 4
Reference numerals 1a, 41b, 41c, and 41d denote laser beams emitted from one laser diode and scanned by one surface of the polygon mirror. Laser beams 42a, 42b, 42c, and 42 are emitted by the next surface of the polygon mirror.
d is scanned. Similarly, the laser beams 43a, 43
b, 43c, and 43d indicate laser beams scanned by the next surface, and laser beams 44a, 44b, 44c, and 44d indicate laser beams scanned by the next surface.

In the above-mentioned invention, the number of laser beams generated from one scanner unit can be any number of two or more in principle.

As described above, by using a plurality of laser beams that scan the surface of the photosensitive drum at equal intervals, a higher-speed image forming apparatus, for example, a four-color full-color laser beam printer can be configured. Further, the resolution in the sub-scanning direction can be easily increased.

In the embodiments described above, the present invention
Although the case where the present invention is applied to a full-color image forming apparatus has been described, it goes without saying that the present invention is also applicable to a single-color image forming apparatus.

[0050]

As described above, according to the present invention,
By scanning the surface of the image carrier with a plurality of laser beams generated from the exposure unit, the process speed can be increased without deteriorating image quality such as color misregistration.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a perspective view illustrating an interval between two laser beams in Embodiment 1.

FIG. 3 is a diagram illustrating an example of an interval between two laser beams.

FIG. 4 is a diagram illustrating another example of the interval between two laser beams.

FIG. 5 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a second embodiment.

FIG. 6 is a diagram showing a state where scanning is performed with four laser beams in the third embodiment.

[Explanation of symbols]

11a, 11b, 11c, 11d Exposure means (laser scanner) 18a, 18b, 18c, 18d, 61 Image carrier (photosensitive drum) 63a, 63b, 63c, 63d Exposure means (laser scanner) Δa, Δb, Δc, Δd Scan direction width

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/113 H04N 1/04 D 5C071 / 29 104A F-term (Reference) 2C362 BA52 BA57 BA61 BA71 CA22 CA39 CB08 CB14 2H030 AA01 BB02 BB12 2H045 BA22 BA33 BA34 DA04 2H076 AB06 AB12 AB68 DA11 EA01 5C072 AA03 BA03 BA19 HA02 HA06 HA13 HB08 QA17 XA01 5C074 AA10 AA12 BB03 BB26 CC22 CC26 DD14 DD15 DD24 GG15 GG15 GG15 GG15 GG15 GG15 GG15 GG15 GG15 GG15 GG15 GG15 GG15

Claims (5)

[Claims] 1. An image forming apparatus comprising: an image carrier; and an exposure unit configured to scan a charged surface of the image carrier to form an electrostatic latent image. Laser oscillation means for generating a plurality of individually modulated laser beams, and multi-beam scanning means for scanning the surface of the image carrier with the plurality of laser beams generated from the laser oscillation means, The multi-beam scanning means moves the plurality of laser beams in the scanning direction at different positions in the sub-scanning direction at the same time, and the portion irradiated by the plurality of laser beams along the sub-scanning direction. Wherein the width of each of the plurality of exposure units is the same. 2. The image forming apparatus according to claim 1, further comprising: a plurality of said image carriers; and at least one exposing unit arranged to face each image carrier. 3. The image forming apparatus according to claim 1, further comprising: a plurality of the exposing units arranged so as to face one image carrier. 4. A width of a portion irradiated by a plurality of laser beams of the exposure unit along a sub-scanning direction is defined as:
The image forming apparatus according to claim 1, wherein the resolution of the image carrier in the sub-scanning direction is the same. 5. A width of a portion irradiated by a plurality of laser beams of the exposure unit along a sub-scanning direction is defined as:
4. The image forming apparatus according to claim 1, wherein the resolution of the image carrier in the sub-scanning direction is an odd multiple.