JP3084893B2 - Image forming device - Google Patents

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 an electronic copying machine or a printer, and more particularly to a developing apparatus such as a two-color laser printer in which a plurality of developing devices use toners of different recording colors to form a plurality of colors. The present invention relates to an image forming apparatus that is effective when forming an image.

[0002]

2. Description of the Related Art Many image forming apparatuses such as electrophotographic copying machines and laser printers form an electrostatic latent image on a photoreceptor and develop it with toner to record an image. . Many of such apparatuses record an image in one color, but the image forming apparatus also performs two-color or multi-color recording due to the effects of computer color image processing and multi-color printing. Things are widespread. For example, in laser printers, documents such as forms which were conventionally printed in black on paper with ruled lines and logos preprinted in blue or the like have been widely color-coded in each color and printed, The paper management is simplified and the printing cost is reduced.

FIG. 5 shows a main part of a laser printer conventionally used as an image forming apparatus capable of recording an image in two colors. Around the photosensitive drum 11 of this laser printer, there are two developing devices, a first developing device 12 for developing with a first recording color and a second developing device 13 for developing with a second recording color. Is arranged. In this figure, the photosensitive drum 11 rotates in the direction of arrow 14 (counterclockwise). On the upstream side of the first developing device 12, a charge corotron 15 for initially uniformly charging the surface of the photosensitive drum 11 is arranged. Further, a first laser beam 17 is scanned between the charge corotron 15 and the first developing device 12 by a first laser beam scanning mechanism 16. Also, the first developing device 12 and the second developing device 13
In between, the second laser beam 19 is scanned by the second laser beam scanning mechanism 18.

A first developing device 12 develops a first electrostatic latent image as a negative image formed by scanning with the first laser beam 17 with, for example, black toner, and forms a black image on the surface of the photosensitive drum 11. To create a toner image. The second developing device 13 is a developing device having exactly the same structure as the first developing device 12, and converts a second electrostatic latent image as a positive image formed by scanning with the second laser beam 19 into the first developing device. The toner is developed with a toner having a polarity opposite to that of the toner used in the developing device 12, and for example, a red toner image is added to the surface of the photosensitive drum 11. In this way, two color toner images are formed on the drum surface.

On the downstream side of the second developing device 13, a pre-transfer corotron 21 and a transfer corotron 2
2 are arranged in this order. The pre-transfer corotron 21 plays a role in aligning the polarity of the toner during transfer. Thereafter, the transfer corotron 22 transfers the toner image onto the sheet 25 conveyed in the direction of arrow 24. After the transfer of the photosensitive drum 11, unnecessary toner is removed by a cleaning blade 26, and the photosensitive drum 11 is irradiated with a charge removing lamp 27 to remove unnecessary charges.

FIG. 6 shows an example of a process for forming an image in such an image forming apparatus. This process will be described with reference to FIG.

First, as shown in FIG. 6 (a), the surface of the photosensitive drum 11 is charged to -75 by the charge corotron 15.
It is uniformly charged to 0V. FIG. 6B shows the first state in this state.
1 shows a state where the first laser beam 17 is scanned by the laser beam scanning mechanism 16. The first exposure, that is, the exposure of the negative image, discharges the charge of the exposed portion, and the potential of the portion increases to -100V. In this state, the first image is developed by the first developing device 12 (reversal development).

FIG. 6C shows the state of the first development. During development, the developing bias of the first developing device 12 is set to -430V. Accordingly, the first image potential (−100) scanned by the first laser beam 17 is obtained.
V) is relatively + 330V. Therefore,
The negatively charged black toner 31 is electrostatically attracted to the portion of the first image potential.

FIG. 6D shows a state in which the second laser beam 19 has been scanned thereafter. The second laser beam 19 is applied to the background portion of the image, and the potential of that portion increases to, for example, -350V. The image portion of the positive image created in this way has a voltage of, for example, -740 V due to a change with time.

FIG. 6 (e) shows a state of development by the second developing device 13. At this time, the developing bias is set to -450 V, and the development (regular development) of the second image with the red toner 32 charged to plus (+) is performed. The red toner 32 is electrostatically attracted to the image portion. In this manner, the two color toners 31 and 32 are attracted to the black or red image portion, respectively, and a two color toner image is created.

In such an image forming apparatus in which two images are formed by one charging to develop two colors, the background potential after the positive image exposure is set to the initial charging potential shown in FIG. The potential is set to a substantially intermediate potential of the negative image exposure section shown in FIG. As a result, a so-called well-type potential is formed, and a force for holding the reversal-developed toner image on the surface of the photoconductor is given.

FIG. 7 shows the characteristics of the second laser beam for setting the background potential of -350 V shown in FIG. 6D. The diameter d _{1 of} the second laser beam 19
Is 1 if the maximum value of the beam energy is P ₀
The beam diameter d ₁ at the energy of / e ² was set to be equal to the width of one pixel. For example, 400 dpi
When an image was drawn at a scanning line density of (dots / inch), the beam diameter d ₁ was set to 63.5 μm. In this way, by scanning the background portion of the second image with the second laser beam 19, these portions are set to the background potential.

[0013]

However, in such a conventional image forming apparatus, the photosensitive drum 1 shown in FIG.
When uneven rotation occurs in 1 or vibration occurs in an optical component such as a laser beam scanning mirror (not shown), a part of the toner particles of the first image adheres to the background portion of the second image, and There was a problem that the quality deteriorated.

FIG. 8 is a view for explaining the cause of the toner particles of the first image staining the background portion of the second image.
In this figure, the portion of the background potential of -350 V has an undulation for each scanning line due to the scanning of the light beam.
This undulation is increased when the scanning of the second laser beam 19 (FIG. 5) becomes unbalanced. Then, a phenomenon occurs in which a portion of the toner 31 electrostatically attached to the portion irradiated with the first laser beam 17 (FIG. 5) moves to a more positive potential portion in the background portion. As described above, the energy wall of the well-type potential does not work effectively, and the toner image formed by the reversal development is disturbed, so that the background image is stained.

Accordingly, an object of the present invention is to provide an image forming apparatus which employs a developing method for forming a negative image and a positive image by one charging, and can suppress disturbance of a toner image formed by reversal development. Is to do.

[0016]

According to the first aspect of the present invention, there are provided: (a) a photosensitive member such as a photosensitive drum or a photosensitive belt; and (b) charging means for uniformly applying a charge to the photosensitive member. (C) negative image exposure means for exposing a negative image on the surface of the photoreceptor charged by the charging means;
Only the part irradiated with light by the negative image exposure means
(E) a positive image by scanning the surface of one light body with a light beam whose half-value width is set to be larger than the width of one pixel; And (f) the second exposure is performed only on a portion not irradiated with light by the positive image exposure means.
And a regular developing means for developing the image in the second color by adsorbing the toner.

That is, according to the first aspect of the present invention, the half width of the light beam by the positive image exposure means for setting the potential of the background portion of the positive image is set to be larger than the width of one pixel. Thus, even if the scanning interval of the light beam is slightly deviated, the undulation of the potential is not increased, thereby achieving the above object.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 illustrates the beam diameter of the second laser beam set in the image forming apparatus according to one embodiment of the present invention. Note that the image forming apparatus of this embodiment has the same configuration as that shown in FIG. 5, so that FIG. 5 will be used as it is in the description of the apparatus.

As shown in FIG. 1, in the image forming apparatus of this embodiment, the half width d _1/2 of the second laser beam 19 (FIG. 5) is used.
Is set to be 1.1 times the width d ₀ of one pixel 41. Here, the half width d _1/2 refers to the width of the beam at a position at a half value of the peak value P ₀ of the energy of the second laser beam 19. As is apparent from FIG. 1, the beam diameter becomes larger than the conventional _{one in} which the beam diameter d ₁ at the energy of P ₀ / e ² is one pixel width.

FIG. 2 shows the relationship between the change in the half width and the image disturbance of the first toner image. As is apparent from this figure, the image disorder of the first toner image as the toner image created by the reversal development changes abruptly at the boundary of the value of the width d ₀ of one pixel, When the width is slightly larger than the width d ₀ , image disturbance is significantly reduced. Therefore, in this embodiment, as described above, the half width d of the beam diameter is obtained.
_1/2 is set at a position where the width d ₀ of one pixel 41 is increased by 10%.

The half width d _1/2 of the beam diameter is set to the width d _{0 of} one pixel.
Since the increase slightly increases the image disturbance of the first toner image, it is not necessary to further increase the half width d _1/2 to improve the image disturbance itself of the toner image. Rather, when the half width d _1/2 of the beam diameter is further increased, the width of the second laser beam 19 being overlapped and scanned is increased, and the width of the narrow line elongated in the main scanning direction is reduced. The disadvantage is that Therefore, in the case of special emphasis reproduction of thin lines it needs to be set to the extent that slightly wider than the width d ₀ of the half-value width d _1/2 one pixel 41 of the beam diameter.

FIG. 3 shows the surface potential of the photosensitive drum at the time when a negative image and a positive image are formed in the image forming apparatus of this embodiment. As is apparent from the correspondence with FIG. 7 in the related art, since the height difference of the background potential at -350 V hardly occurs, the energy wall of the well-type potential works effectively. Therefore, the toner 31 electrostatically attached to the portion irradiated with the first laser beam 17 (FIG. 5) remains at the same position, and the image is not disturbed.

In the embodiment described above, an image forming apparatus for recording an image in two colors has been described. However, the present invention is similarly applied to an image forming apparatus for recording an image in three or more colors. it can.

Modification

FIG. 4 shows an image forming apparatus for recording an image in four colors as a modified example of the present invention. This image forming apparatus includes a relatively large transport belt 10.
1 is used. The transport belt 101 moves at a constant speed in the direction of the arrow 102. Conveyor belt 10
1, two photosensitive drums 103 and 104 are in sliding contact with each other. The first and second photosensitive drums 103 and 104 rotate at the same peripheral speed as the conveyor belt 101. Around the first photosensitive drum 103, a first charge corotron 106, first and second developing devices 107 and 108, a transfer corotron 109, and a first cleaning device 111 are arranged downstream in this order. It is arranged facing. Around the second photosensitive drum 104, a second charge corotron 112, third and fourth developing devices 113 and 114, a transfer corotron 115, and a second cleaning device 116 are arranged downstream in this order. It is arranged facing.

Also in this image forming apparatus, a first laser beam 121 is irradiated between the first charge corotron 106 and the first developing device 107, so that the first developing device 107 and the second developing device 108 By irradiating the second laser beam 122 during this time, two-color development can be performed. Similarly, a third laser beam 123 is applied between the second charge corotron 112 and the third developing device 113, and a fourth laser device 123 is applied between the third developing device 113 and the fourth developing device 114. By irradiating the laser beam 124, the remaining 2
Color development can be performed. The recording paper (not shown) is conveyed on the conveyance belt 102 in a direction indicated by an arrow 125,
First, a two-color toner image is transferred by the first photosensitive drum 103, and then the remaining two-color toner images are transferred by the second photosensitive drum 104. Then, the toner image is fixed by a fixing device (not shown).

An image forming apparatus of this type can be regarded as two connected apparatuses having the same configuration as that described in the embodiment. Accordingly, by setting the half width d _1/2 of the diameter of each of the second laser beam 122 and the fourth laser beam 124 to be slightly larger than the width d _{0 of} one pixel, It is possible to prevent the toner image formed by the first laser beam 121 or the third laser beam 123 from being disturbed.

[0029]

As described above, according to the first aspect of the present invention, a positive image is exposed by scanning the surface of the photoreceptor with a light beam whose half-value width is set to be larger than the width of one pixel. Since the means is arranged, it is possible to form an effective well-type potential without having to set the charging potential by the charging means to a particularly high absolute value. Therefore, it is possible to contribute to prolonging the life of the device without causing any unreasonableness in the charging potential by the charging unit.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a beam diameter of a second laser beam set in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating a relationship between a change in a half-value width of a laser beam and image disorder of a first toner image.

FIG. 3 is an explanatory diagram showing the surface potential of the photosensitive drum at the time when a negative image and a positive image are created in the image forming apparatus of the present embodiment.

FIG. 4 is a schematic configuration diagram illustrating an outline of an image forming apparatus according to a modified example of the invention.

FIG. 5 is a schematic configuration diagram schematically illustrating a partial cross section of the image forming apparatus.

6 is an explanatory diagram illustrating an example of a process of forming an image in the image forming apparatus illustrated in FIG.

FIG. 7 is a characteristic diagram showing characteristics of a conventionally used second laser beam.

FIG. 8 is an explanatory diagram showing the surface potential of a photosensitive drum at the time when a negative image and a positive image are created in a conventional image forming apparatus.

[Explanation of symbols]

11 photoreceptor drum, 12, 107 first developing device,
13, 108: second developing device, 15: charge corotron, 17, 121: first laser beam, 19, 12
2 ... second laser beam, 41 ... 1 pixel, 101 ... photosensitive belt, 103 ... first photosensitive drum, 104 ... second
Of the photoconductor drum 106, the first charge corotron,
112: second charge corotron, 113: third developing device, 114: fourth developing device, 123: third laser beam, 124: fourth laser beam, d1 _{/ 2} : half width, d ₀ ... one pixel width

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI G03G 15/043 (72) Inventor Tsuneya Kajiura 3-7-1, Funai, Iwatsuki City, Saitama Prefecture Fuji Xerox Co., Ltd. Iwatsuki Office (72 ) Inventor Yoshifumi Ozaki 3-7-1 Fuchu, Iwatsuki-shi, Saitama Fuji Xerox Co., Ltd. Iwatsuki Office (56) References JP-A-55-83070 (JP, A) JP-A-2-281272 (JP, A) JP-A-2-293765 (JP, A) JP-A-63-296069 (JP, A) JP-A-4-50975 (JP, A) JP-A-63-292157 (JP, A) JP-A-2-185454 (JP, A) JP-A-4-60654 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/01 G03G 15/01-15/01 117 G03G 15/04- 15/04 120 B41J 2/44

Claims (1)

(57) [Claims] 1. A photoconductor, a charging unit for uniformly applying a charge on the photoconductor, a negative image exposure unit for exposing a negative image on a surface of the photoconductor charged by the charging unit, and a negative image exposure. First place only on the part irradiated with light by means
Reversal developing means for developing an image in the first color by adsorbing the toner, and exposing a positive image by scanning the surface of the photoreceptor with a light beam having a half-value width larger than the width of one pixel. A positive image exposing means; and a regular developing means for developing the image in the second color by adsorbing the second toner only to a portion not irradiated with the light by the positive image exposing means. Image forming device.