JPH09185193A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of making the potential by electrification of a photoreceptor at the time of starting the formation of an image almost equal to the one at the time of continuing the formation of the image thereafter and preventing the occurrence of irregularities of the image density. SOLUTION: In the image forming device provided with the photoreceptor 1, an electrifying roller 2, an exposure device 3, a developing device 4, a transfer belt 5 and a discharge lamp 7, at the time of starting the formation of the image, the photoreceptor 1 is electrified by the electrifying roller 2 and then destaticized by the discharge lamp 7. Further, the photoreceptor 1 is electrified by the electrifying roller 2 again and then, exposed by the use of exposure device 3 to form an electrostatic latent image.

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, a printer and a facsimile machine which uses an electrophotographic process.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, the surface of a drum-shaped or belt-shaped photosensitive member is charged by a charging device and then exposed by an exposure device to form an electrostatic latent image. After the electrostatic latent image is visualized by the developer from the developing device, it is transferred onto the transfer material conveyed from the paper feeding device by using the transfer device and fixed by the fixing device. .

In such an image forming apparatus, when the image formation is started, the surface of the photoconductor charged by the charging device is immediately exposed by the exposure device to form an electrostatic latent image. .

[0004]

However, in the conventional image forming apparatus, there is a problem that when the image formation is started, so-called density unevenness occurs in which the density changes in the middle of the image. This is because at the start of image formation,
There are a part where the photoconductor is charged only once and a part where it is charged the second time, and when the charging potential of the photoconductor is charged only once and when it is charged twice or more. This is a phenomenon that occurs because they are different.

The present invention has been made in view of the above problems, and an object of the present invention is to charge the photoconductor at the start of image formation and charge potential of the photoconductor at the time of continuing image formation thereafter. Is substantially equal to each other, and an image forming apparatus in which the occurrence of image density unevenness is prevented is provided.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention charges a rotating photoconductor and the photoconductor, which is sequentially arranged in the turning direction of the photoconductor, to a predetermined polarity. Charging means, exposing means for exposing the photoconductor charged by the charging means to form an electrostatic latent image, developing means for developing the electrostatic latent image formed by the exposing means, and the developing means. An image forming apparatus comprising: a transfer unit that transfers a developed image developed by a transfer unit onto a transfer material; and an optical charge removing unit that irradiates the surface of the photoconductor after the transfer by the transfer unit with light to remove the residual potential. At the start of formation, the photosensitive member is charged by the charging unit, then discharged by the optical charge removing unit, further charged by the charging unit, and then exposed by the exposing unit to form an electrostatic latent image. To be formed There is provided an image forming apparatus, characterized in that the.

Further, the above charging means provides an image forming apparatus which is a contact type charging means for contacting the above-mentioned photoconductor to give an electric charge thereto.

The contact type charging means provides an image forming apparatus which is a contact type charging means to which only a DC voltage is applied.

Further, the present invention provides an image forming apparatus in which the photosensitive member is rotated faster than the speed at which the image is formed until just before the exposure by the exposing means.

[0010]

According to the present invention, at the start of image formation, the photosensitive member is charged by the charging means, then discharged by the photo-erasing means, further charged by the charging means, and then electrostatically latent by the exposing means. Since an image is formed, the charging potential of the photoconductor at the start of image formation and the charging potential of the photoconductor at the time of continuing image formation thereafter become substantially equal.

Further, according to the present invention, in the image forming apparatus having the contact type charging means, the charging potential of the photoconductor at the start of image formation is substantially equal to the charging potential of the photoconductor at the time of continuing image formation thereafter. .

Further, according to the present invention, in the image forming apparatus in which only the DC voltage is applied to the contact type charging means, the charging potential of the photoconductor at the start of image formation and the charge potential of the photoconductor at the time of continuing image formation thereafter. The charging potentials are almost equal.

Further, according to the present invention, at the start of image formation, the time required for the photosensitive member to be charged by the charging unit, then discharged by the optical discharging unit, and further charged by the charging unit is shortened. , The first copy time is shortened.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. First, a first embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a schematic block diagram showing an embodiment of the image forming apparatus of the present invention. As shown in the figure, the image forming apparatus includes a charging roller 2, which is a charging unit, an exposure unit 3, which is an exposing unit, a developing unit 4, which is a developing unit, a transfer belt 5, which is a transferring unit, and a cleaning unit around a photoconductor 1. A cleaning device 6, which is a unit, and a discharge lamp 7, which is a discharging unit, are arranged along the rotation direction of the photoconductor 1 indicated by an arrow in the drawing. Image formation by the present image forming apparatus is performed by the well-known Carlson electrophotographic method, and as the photoconductor 1, an OPC photoconductor having photoconductivity for negative charging and having a diameter of 60 mm was used.

First, the operation during continuous image formation will be described. The photoconductor 1 is charged by the charging roller 2.
That is, the charging roller 2 comprises a stainless steel cored bar provided with an elastic layer made of epichlorohydrin rubber, and a coating material obtained by mixing and blending fluorine-based Lumiflon and epichlorohydrin rubber is applied to the surface thereof. A DC voltage of -1.5 KV is applied by the power source. Therefore, the photoconductor 1 was charged to -800V.
Next, the photoreceptor 1 is irradiated with the image light by the laser light from the exposure device 3. The image light is for illuminating the character portion to attenuate the potential of the photoconductor. As a result of the image exposure,
The potential of the character portion was attenuated to −100 V, and a negative-positive electrostatic latent image was formed on the photoconductor 1.

Next, the electrostatic latent image on the photoconductor 1 is developed by the developing device 4. The developing device 4 is a well-known two-component developing device, and has negatively charged toner and brass-charged carrier, and a developing bias of −600 V is applied to the developing roller. Therefore, in the electrostatic latent image on the photoconductor 1, the character portion was developed by the negatively charged toner. The developed image thus obtained reaches the contact portion of the transfer belt 5 as the photoconductor 1 rotates. At this time, a transfer sheet (not shown), which is a transfer material, is conveyed to the contact portion, but +3 KV is applied to the transfer belt 5.
Since the voltage is applied, the negatively charged toner moves from the photoconductor 1 to the transfer sheet and is transferred.

The toner image transferred to the transfer paper in this manner is fixed on the transfer paper by the action of a fixing device (not shown) by the conveyance of the transfer paper. On the other hand, the residual toner remaining on the photoconductor 1 at the time of transfer by the transfer belt 5 is removed from the photoconductor 1 by the cleaning device 6, and the photoconductor 1 whose surface has been cleaned has the residual charge removed by the charge eliminating lamp 7. Will be used for the next image forming process.

By the way, as described above, at the start of image formation, the photosensitive member 1 is charged only once, and as a result of the rotation of the photosensitive member 1, the photosensitive member 1 is charged twice or more. The potential of the portion charged only once is lower than the potential of the portion charged twice or more. In this example, 1
The portion charged only once was only charged to -700V, but the once charged portion was discharged by the discharging lamp and then the charging potential was -800V when the second charging potential was performed.

The image forming apparatus according to the present embodiment employs the reversal developing method, and the developing bias is -6 in order to adapt to the potential of the photosensitive member when the developing bias is charged twice or more.
Since the voltage is set to 00V, the potential of the non-image portion (background portion) of the portion charged only once at the start of image formation is -700.
V is not sufficient to prevent the adhesion of the developer, and as a result, a thin developer adhesion (background stain) occurs. When the regular developing method is adopted as the developing method, the above phenomenon appears as a decrease in the density of the image area.

Therefore, in this embodiment, when a latent image is formed on the photoconductor 1 at the start of image formation, the charging roller 2 is first charged, then the discharging lamp 7 is used for discharging, and the charging roller is again charged. A latent image is formed by the exposure device 3 on the surface of the photoconductor charged by 2.

FIG. 2 shows the sequence of this embodiment. First, after the print signal is input, the photoconductor 1 starts rotating with a predetermined rising time. Then, after the photosensitive member 1 reaches the steady rotation, the voltage application to the charging roller 2 is turned on and the charging of the photosensitive member 1 is started. Next, the voltage application to the static elimination lamp 7 is turned on after a time t ₁ from the start of charging, and at this time t ₁ , the surface of the photoconductor is removed from the charging roller 2 during the steady rotation of the photoconductor 1. It is set shorter than the time to reach. Further, the laser output from the exposure device 3 is turned on after the time t ₂ from when the charging roller 2 is turned on. This time t ₂ is the time required for the surface of the photoconductor 1 to make one revolution during the steady rotation of the photoconductor 1. Is set longer than.

Therefore, in the present embodiment, the exposure device 3
Since the surface of the photosensitive member 1 exposed by means of the effects of charging, discharging, and charging in order, the charging potential is substantially the same as the charging potential when image formation is continued even at the start of image formation. . Therefore, the density does not change during image formation. In this embodiment, a contact charging type charging roller is used as the charging means, but the contact charging means such as the charging roller has a charging ability higher than that of the non-contact charging means such as the corona discharge device. Is low, the result of charging is likely to be affected by the potential of the photosensitive member before charging, and when the voltage applied to the contact charging means is only the DC voltage, the effect is further increased. Therefore, in applying the present invention, the image forming apparatus having the contact charging means is particularly useful, but it is also applicable to the image forming apparatus using the non-contact type charging means.

Next, a second embodiment of the present invention will be described.
The second embodiment is different from the first embodiment in that the photosensitive member 1 is exposed until the exposure device 3 exposes it.
The point is that the photoconductor 1 is rotated at a speed higher than that during normal image formation.

That is, the photosensitive member 1 starts to rotate at the first predetermined speed with a predetermined rising time after the print signal is input, as in the sequence shown in FIG.
Then, after the photoconductor 1 reaches the steady rotation of the first predetermined speed, the voltage application to the charging roller 2 is turned on and the photoconductor 1 is rotated.
Charging is started. Next, after a lapse of time t ₃ from the start of charging, the voltage application to the charge eliminating lamp 7 is turned on. At this time t ₃ , the surface of the photoconductor is charged while the photoconductor 1 is rotating at the first predetermined speed. It is set to be shorter than the time required to reach the static elimination lamp 7 from the roller 2. Then, after a lapse of time t ₄ after the charging roller 2 is turned on, the photosensitive member 1 is decelerated to a second image forming speed slower than the first speed with a predetermined fall time. Then, the laser output from the exposure device 3 is turned on at time t ₅ after the charging roller 2 is turned on. The time t ₄ is shorter than the time t _5, time t ₅ is set longer than the time required to round the surface of the photoreceptor.

Therefore, the time from the start of rotation of the photosensitive member 1 to the start of latent image formation by the exposure device 3 is shorter than that in the first embodiment, and the image forming time for the first sheet is shortened. . In this embodiment, in order to make the rotation speed of the photoconductor 1 variable, the photoconductor 1 is driven by a single motor (not shown) that drives only the photoconductor 1. Further, in both the first and second embodiments, control of voltage application to the charging roller 2, control of voltage application to the discharge lamp 7,
The control of the laser output in the exposure device 3 and the control relating to the driving of the photoconductor 1 were performed using a well-known CPU (not shown).

[0027]

As described above, according to the present invention, at the start of image formation, the photosensitive member is charged by the charging means, then discharged by the optical discharging means, and further charged by the charging means. After that, since the electrostatic latent image is formed by the exposure means, the charging potential of the photoconductor at the start of image formation becomes substantially equal to the charging potential of the photoconductor at the time of continuing image formation thereafter, preventing uneven density. To be done.

Further, according to the present invention, it is possible to prevent the occurrence of the density unevenness in the image forming apparatus equipped with the contact type charging means, which easily causes the density unevenness.

Further, according to the present invention, it is possible to prevent the occurrence of density unevenness in the image forming apparatus equipped with the contact type charging means to which only the DC voltage is applied, in which density unevenness is likely to occur.

Further, according to the present invention, at the start of image formation, the time required for the photosensitive member to be charged by the charging means, then discharged by the optical discharging means, and further charged by the charging means is shortened. Therefore, it is possible to prevent the occurrence of density unevenness without reducing the first copy time.

[0031]

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a timing chart of a sequence according to the first embodiment of the present invention.

FIG. 3 is a timing chart of a sequence according to the second embodiment of the present invention.

[Explanation of symbols]

 1 Photoreceptor 2 Charging Roller 3 Exposure Device 4 Developing Device 5 Transfer Belt 7 Electrification Lamp

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeru Watanabe 1-3-6 Nakamagome, Ota-ku, Tokyo Stock company Ricoh Company (72) Inventor Hiroshi Saito 1-3-6 Nakamagome, Ota-ku, Tokyo Share Inside Ricoh Company (72) Inventor Toshiyuki Uchida 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd.

Claims (4)

[Claims] 1. A rotating photoconductor, charging means for sequentially charging the photoconductor to a predetermined polarity, which is arranged in the rotating direction of the photoconductor, and a photoconductor charged by the charging means. Exposure means for exposing an image to form an electrostatic latent image, developing means for developing the electrostatic latent image formed by the exposing means, and transfer means for transferring the developed image developed by the developing means onto a transfer material. And an optical charge erasing unit for irradiating light to the surface of the photoconductor after transfer by the transfer unit to remove residual potential, the photoconductor is charged by the charging unit at the start of image formation. An image forming apparatus is characterized in that an electrostatic latent image is formed by receiving static electricity by the photo static elimination means, charging by the charging means, and then exposure by the exposure means. . 2. The image forming apparatus according to claim 1, wherein the charging unit is a contact type charging unit that contacts the photosensitive member and applies an electric charge thereto. 3. The image forming apparatus according to claim 2, wherein the contact type charging means is a contact type charging means to which only a DC voltage is applied. 4. The image forming apparatus according to claim 1, wherein the photosensitive member is rotated faster than an image forming speed until just before the photosensitive member is exposed by the exposing means. An image forming apparatus characterized by the above.