JP3330739B2 - 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 a copying machine and a printer.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, a photoreceptor is rotated by a photoreceptor driving unit, uniformly charged by a charging unit, and thereafter, light is written on the photoreceptor by light irradiation by an exposure unit. To form a negative electrostatic latent image. The electrostatic latent image is visualized as a toner image by negative / positive reversal development by a developing unit, and an intermediate transfer member such as an intermediate transfer belt is brought into contact with and separated from the photosensitive member. The toner image on the photoreceptor is transferred to the intermediate transfer body while being rotated by contact with the photoreceptor, and after the transfer of the toner image in a predetermined image forming area on the photoreceptor is completed, the photoreceptor and the intermediate transfer body are separated by the contact / separation means There is something to make.

As an image forming apparatus using such an intermediate transfer member, there is a color copying apparatus and the like. In a color copying apparatus, electrostatic latent images of a plurality of colors are sequentially formed on a photoreceptor, developed by a developing unit, and an intermediate transfer member is brought into contact with the toner image of each color on the photoreceptor when the toner image passes through a transfer area. The intermediate transfer member is separated from the photoconductor by the contacting / separating device when the non-image forming area on the photoconductor passes through the transfer area by being brought into contact with the photoconductor by the separating device.

[0004] JP-A-1-166070 and JP-A-1
In JP-A-293380 and JP-A-2-18591, each toner image is repeatedly transferred from the photosensitive member to an intermediate transfer member such as an intermediate transfer belt without directly transferring the toner image from the photosensitive member to transfer paper. An image forming apparatus that collectively transfers the image to transfer paper later is described. Further, Japanese Patent Application Laid-Open No. 1-273074 discloses an image forming apparatus for bringing a photoconductor and an intermediate transfer belt into and out of contact with each other.

[0005]

In the above-described image forming apparatus, when the photosensitive member and the intermediate transfer member are moved from the contact state to the separated state, the speed of the photosensitive member may fluctuate. That is, the negative electrostatic latent image on the photosensitive member is
When the toner image is visualized as a toner image by the positive reversal development, the surface potential of the photoconductor is adjusted to a non-image area (background area) in an image forming area on the photoconductor or a non-image area (color image) between image forming areas. During the preparation, for example, between the rear end of the first color toner image and the front end of the second color toner image) remains almost charged. For this reason, when the photosensitive member and the intermediate transfer member are rotating while being in contact with each other, an electrostatic attraction force is generated by the charged charges of the photosensitive member, and the intermediate transfer member is strongly attracted to the photosensitive member. When the intermediate transfer body is separated from the photoconductor in such a state, a large load fluctuation is applied to the photoconductor drive unit that drives the photoconductor, and the speed fluctuation of the photoconductor may occur due to the influence. .

When the next image is optically written by the exposure means and negative / positive reversal development is performed by the developing means when the speed fluctuation of the photosensitive member occurs, the displacement, banding, and image disturbance of the color image due to the expansion and contraction of the image occur. Occurs and the image quality deteriorates.

The present invention solves the above-mentioned problems and eliminates the electrostatic attraction force at the time of the separating operation between the photosensitive member and the intermediate transfer member, thereby preventing the deterioration of the image quality due to the fluctuation of the photosensitive member speed. The purpose is to provide.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a photoreceptor is rotated and uniformly charged by a charging means, and then the photoreceptor is negatively irradiated by light irradiation by an exposure means. An electrostatic latent image is formed, this electrostatic latent image is visualized as a toner image by reversal development by a developing unit, and the toner image on the photoconductor is rotated while the intermediate transfer member is brought into contact with the photoconductor and rotated. An image forming apparatus which transfers the toner image to the intermediate transfer member and separates the photosensitive member from the intermediate transfer member after the transfer of the toner image in a predetermined image forming area on the photosensitive member is completed; Means for lowering the charging potential of the image area and separating the photosensitive member and the intermediate transfer member at a timing when the predetermined non-image forming area becomes a transfer portion area.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the charging potential of a predetermined non-imaging area between the image forming areas on the photosensitive member is set upstream of the transfer area. The image forming apparatus is provided with means for reducing the charge potential of the non-image forming area by removing static electricity.

[0010] The third aspect of the present invention is the first or second aspect.
In the above image forming apparatus, the means for lowering the charging potential of the non-image forming area is provided between a developing area and a transfer section area, and adjusts a charging potential of the photoconductor to a rear end of the toner image on the photoconductor. At a predetermined timing after passing through and until the next toner image on the photoconductor arrives, to lower the charged potential in a predetermined non-image forming area.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the charging unit is configured to move the non-image forming area between the preceding image forming area and the next image forming area on the photoconductor. The predetermined non-image forming area is temporarily turned off to partially remove the static electricity.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the non-image forming area between the preceding image forming area and the next image forming area on the photosensitive member by the exposure means. Is to temporarily erase the charge on the photoreceptor so as to neutralize the predetermined non-image forming area.

[0013] The invention according to claim 6 is the invention according to claims 1, 2, and 3.
6. The image forming apparatus according to 3, 4, or 5, wherein a length of the predetermined non-image forming area is at least a transfer nip width or more.

The invention according to claim 7 is the invention according to claims 1, 2, and
7. The image forming apparatus according to 3, 4, 5, or 6, wherein the start timing of the substantial separation operation between the photosensitive member and the intermediate transfer member is determined by setting a predetermined non-image forming area on the photosensitive member to a transfer nip width. This is after the time when it is almost relative to the entire area.

[0015] The invention according to claim 8 is based on claims 1, 2, and
7. The image forming apparatus according to 3, 4, 5 or 6, wherein the end timing of the substantial separation operation between the photosensitive member and the intermediate transfer member is determined by setting a predetermined non-image forming area on the photosensitive member to a transfer nip width. This is a state in which it is opposed to almost the entire area.

The invention according to claim 9 is the invention according to claim 4 or 5.
In the above-described image forming apparatus, the developing unit is deactivated so that toner does not adhere to a predetermined non-image forming area on the photoconductor.

According to a tenth aspect of the present invention, in the image forming apparatus according to the second or third aspect, the static eliminator is a light irradiator for erasing the photoconductor by light irradiation.

According to an eleventh aspect of the present invention, in the image forming apparatus of the second or third aspect, the static elimination means is a corona discharger.

[0019]

According to the first aspect of the present invention, the charging potential of a predetermined non-image forming area on the photoreceptor is reduced, and the photoreceptor and the intermediate transfer body are switched at the timing when the predetermined non-image forming area becomes the transfer area. Are separated.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the charge potential of a predetermined non-image forming area between the image forming areas on the photosensitive member is neutralized upstream of the transfer section area. By doing so, the charged potential of the non-image forming area is reduced.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the means for lowering the charging potential of the non-image forming area includes a photosensitive member between the developing area and the transfer area. After the trailing edge of the toner image on the photoconductor passes through the charging potential and at a predetermined timing until the next toner image on the photoconductor arrives, the charge is removed at a predetermined timing to lower the charging potential of a predetermined non-image forming area. I do.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the charging unit is a part of the non-image forming area between the preceding image forming area and the next image forming area on the photosensitive member. To temporarily turn off, and a predetermined non-imaging area is neutralized.

According to a fifth aspect of the present invention, in the image forming apparatus of the first aspect, a part of the non-image forming area between the preceding image forming area and the next image forming area on the photosensitive member by the exposure means. As a result, the charge on the photosensitive member is temporarily erased, and a predetermined non-image forming area is neutralized.

According to the sixth aspect of the present invention, there is provided the first, second, and third aspects.
6. The image forming apparatus according to 3, 4, or 5, wherein a length of the predetermined non-image forming area is at least equal to or greater than a transfer nip width.

According to the seventh aspect of the present invention, there is provided the first, second, third and fourth aspects.
In the image forming apparatus described in 3, 4, 5 or 6, the start timing of the substantial separation operation between the photosensitive member and the intermediate transfer member is such that the predetermined non-image forming region on the photosensitive member is substantially the entire region of the transfer nip width. After that.

In the invention according to claim 8, claims 1, 2,
In the image forming apparatus as set forth in 3, 4, 5 or 6, the end timing of the substantial separation operation between the photosensitive member and the intermediate transfer member is determined by setting a predetermined non-image forming area on the photosensitive member to substantially the entire area of the transfer nip width. It is a state opposite to.

According to a ninth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, the developing means does not operate so that the toner does not adhere to a predetermined non-image forming area on the photosensitive member. .

According to a tenth aspect of the present invention, in the image forming apparatus according to the second or third aspect, the static elimination means comprising a light irradiating static eliminator removes static electricity by irradiating the photosensitive member with light.

According to an eleventh aspect of the present invention, in the image forming apparatus according to the second or third aspect, the charge removing means comprising a corona discharger removes the charge potential of the photosensitive member.

[0030]

FIG. 2 schematically shows a first embodiment of the present invention, FIG. 3 shows an enlarged view of a portion around the photosensitive drum and the intermediate transfer belt, and a solid line in FIG. The operation timing is shown. This first embodiment is described in claims 1-3, 6-
Embodiments of the invention described in 8, 10, and 11 are examples of an electrophotographic color image forming apparatus including a color copying apparatus using an intermediate transfer belt as an intermediate transfer member. This color copying apparatus can be roughly classified into a structure and a color image reading apparatus (hereinafter referred to as a color scanner) 1 and an electrophotographic color image recording apparatus (hereinafter referred to as a color printer).
And 2.

First, the color scanner 1 illuminates the original 4 on the original table 3 with the illumination lamp 5, and reflects the reflected light image via the mirror groups 6 to 8 and the lens 9.
0 and the illumination lamp 5 and the movable optical system 6-
The scanner 8 is moved by a scanner motor to read color image information of a document by color separation for each of blue, green, and red, for example, and to convert it into an electric image signal.

An image signal of each color obtained by the color sensor 10 is subjected to color conversion processing by an image processing unit as image processing means based on its intensity level, and is subjected to black (hereinafter referred to as BK) and cyan (hereinafter referred to as BK). C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) color image data.

The color printer 2 uses the BK, C, M, and Y color image data from the image processing unit to output BK,
Visual images of C, M, and Y are formed, and these are superimposed to create a four-color full-color image. Next, the color printer 2 will be described. The writing optical unit 11 converts the color image data from the image processing unit into an optical signal and performs optical writing corresponding to a document image on a photosensitive member 12 composed of a photosensitive drum to form an electrostatic latent image. The writing optical unit 11 includes a laser 13 and a laser 13.
A polygon mirror 14 for deflecting the laser light from the lens, a motor 15 for rotating the polygon mirror 14, an f / θ lens 16, a reflection mirror 17, etc., and the laser light from the polygon mirror 14 is reflected by the f / θ lens 16 Mirror 1
The image is formed on the photosensitive drum 12 via the image forming unit 7.

The photoreceptor drum 12 is driven by a photoreceptor drum drive motor and rotates counterclockwise as indicated by an arrow. Around the photoreceptor cleaning device (including a pre-cleaning charge remover 18) 19, the photosensitive drum 12 serves as a charge removing means. , A charging unit 21 as a charging unit, a potential sensor 22, developing units (BK developing unit 23, C developing unit 24, M developing unit 25, Y developing unit 26), a development density pattern detector 2
7, a pre-transfer neutralizer 28, an intermediate transfer member 29 including an intermediate transfer belt, and the like are arranged.

Each of the developing devices 23 to 26 is a photosensitive drum 12
A developing sleeve 23 that rotates by bringing a developer spike into contact with the surface of the photosensitive drum 12 to develop the electrostatic latent image thereon;
a, 24a, 25a, 26a, and developing paddles 23b, 24 rotating to pump up and agitate the developer therein.
b, 25b, 26b and toner concentration detection sensors 23c, 24c, 25c, 2 for detecting the toner concentration of the developer.
6c and the like. In the standby state, all of the four developing units 23 to 26 are set to the developing sleeves 23a, 24a, and 25.
a and 26a are in the state of the cutting of the developer (development inoperative), but the order of each developing operation of the developing units 23 to 26 (B
The order of image formation of K, C, M, Y) is BK, C, M, Y
The order of developing the electrostatic latent image is as follows. However, the order of image formation for each color is not limited to this, and may be any order.

At the start of the copying operation, the photosensitive drum 12
Rotates and is uniformly charged by the charger 21. Then, the color scanner 1 starts reading for obtaining BK image data at a predetermined timing. The image processing unit obtains BK image data from the image data from the color scanner 1 and writes the BK image data based on the BK image data. The unit 11 performs optical writing on the photosensitive drum 12 by laser light to form a latent image. Hereafter, this BK
An electrostatic latent image based on image data is called a BK latent image. C, M,
The electrostatic latent image based on each image data of Y is also a C latent image and M
The latent image is referred to as a Y latent image. In order to make the BK latent image developable from the leading end thereof, the developing sleeve 23a starts rotating before the BK latent image leading end reaches the developing position of the BK developing unit 23, and the developer is brushed. The BK latent image is developed with BK toner.

Thereafter, the developing operation of the BK latent image area on the photosensitive drum 12 is continued, but when the rear end of the BK latent image passes the BK developing position, the developing operation on the developing sleeve 23a of the BK developing unit 23 is promptly performed. The cutting of the agent is performed, and the development is disabled. This is completed at least before the leading end of the C latent image based on the next C image data arrives. The cutting of the developer is performed by switching the rotation direction of the developing sleeve 23a to a direction opposite to that during the developing operation. At this time, the other developing devices 24
Nos. To 26 remain in a development inoperative state.

The BK toner image on the photosensitive drum 12 is transferred to the surface of an intermediate transfer belt 29 driven at a constant speed with the photosensitive drum 12 (hereinafter, the BK toner image is transferred from the photosensitive drum 12 to the intermediate transfer belt 29). The toner image transfer is referred to as a belt transfer). The belt transfer is performed when the photosensitive drum 12 and the intermediate transfer belt 29 are in contact with each other.
This is performed by applying a predetermined bias voltage from a high-voltage power supply to the transfer bias roller 30 that is in contact with the transfer bias roller 9. The intermediate transfer belt 29 is pressed against the photosensitive drum 12 at a predetermined timing by a contact / separation mechanism when performing the belt transfer, and is separated from the photosensitive drum 12 at a predetermined timing by the contact / separation mechanism when the belt transfer is not performed.

After the transfer of the BK toner image, the photosensitive drum 12 is neutralized and cleaned by a photosensitive body cleaning device 19 including a pre-cleaning neutralizer 18, is neutralized by a neutralization lamp 20, and is uniformly charged again by a charger 21. . The intermediate transfer belt 28 transfers the toner images of BK, C, M, and Y sequentially formed on the photosensitive drum 12 while sequentially aligning and transferring them on the same surface.
A belt transfer image of color superposition is formed, and then the belt transfer image is collectively transferred to transfer paper. The configuration and operation of the intermediate transfer belt unit including the intermediate transfer belt 28 will be described later.

On the photosensitive drum 12 side, the process proceeds to the C image forming process after the BK image forming process. In the C image forming process, the color scanner 1 starts reading for obtaining C image data at a predetermined timing. The image processing unit obtains the C image data from the image data from the color scanner 1, and writes the C optical data based on the C image data.
Performs optical writing on the photosensitive drum 12 with laser light to form a C latent image.

The developing sleeve 24a starts rotating after the rear end of the previous BK latent image has passed and before the leading end of the C latent image has reached the developing position. And develop the C latent image with C toner. Since then
The C developing device 24 continues to develop the C latent image area on the photosensitive drum 12, but when the rear end of the C latent image passes, the C
As in the case of the K developing device 23, the developer is cut off on the C developing sleeve 24a. This is also completed before the leading end of the next M latent image arrives.

The C toner image on the photosensitive drum 12 is transferred to the intermediate transfer belt 2 driven at the same speed as the photosensitive drum 12.
9 is transferred to the surface. After the transfer of the C toner image, the photosensitive drum 12 is neutralized and cleaned by a photosensitive body cleaning device 19 including a pre-cleaning neutralizer 18, is neutralized by a neutralization lamp 20, and is uniformly charged again by a charger 21.

On the photosensitive drum 12 side, the process proceeds to the M image forming process after the C image forming process. In the M image forming process, the color scanner 1 starts reading for obtaining M image data at a predetermined timing. The image processing unit obtains M image data from the image data from the scanner 1, and based on the M image data, the writing optical unit 11 performs optical writing on the photosensitive drum 12 by laser light to form an M latent image.

The M developing unit 25 starts rotating the developing sleeve 25a with respect to the developing position after the rear end of the C latent image has passed and before the leading end of the M latent image has arrived. And develop the M latent image with M toner. Hereafter, M
The developing unit 25 continues to develop the M latent image area on the photosensitive drum 12, but when the rear end of the M latent image passes, the developing unit 25 Cut the developer. This is also completed before the leading end of the next Y latent image arrives.

The M toner image on the photosensitive drum 12 is transferred to the intermediate transfer belt 2 driven at the same speed as the photosensitive drum 12.
9 is transferred to the surface. After the transfer of the M toner image, the photoconductor drum 12 is subjected to static elimination and cleaning by a photoconductor cleaning device 19 including a pre-cleaning static eliminator 18, is neutralized by a neutralization lamp 20, and is uniformly charged again by a charger 21.

On the photosensitive drum 12 side, the process proceeds to the Y image forming process after the M image forming process. In the Y image forming process, the color scanner 1 starts reading for obtaining Y image data at a predetermined timing. The image processing unit obtains Y image data based on the image data from the scanner 1, and based on the Y image data, the writing optical unit 11 performs optical writing on the photosensitive drum 12 by laser light to form a Y latent image.

The developing sleeve 26a starts rotating with respect to the developing position after the rear end of the preceding M latent image has passed and before the leading end of the Y latent image has arrived. And the Y latent image is developed with the Y toner. Hereafter, Y
The developing device 26 continues the development of the Y latent image area on the photosensitive drum 12, but when the rear end of the Y latent image passes, the developing device 26 on the Y developing sleeve 26a is similar to the case of the preceding M developing device 25. Cut the developer. This is also completed after the rear end of the Y latent image has arrived. The Y toner image on the photosensitive drum 12 is transferred to the intermediate transfer belt 29 driven at the same speed as the photosensitive drum 12.
Is transferred to the surface of

Next, the intermediate transfer belt unit will be described. The intermediate transfer belt 29 includes a belt transfer bias roller 30, a driving roller 31, and a driven roller group 32-3.
4, the driving roller 31 is driven by an intermediate transfer belt driving motor, which will be described later, and the intermediate transfer belt 2
9 rotates. A belt cleaning device (belt cleaner) 35 serving as a cleaning unit includes a brush roller 35.
a, a rubber blade 35b, a contact / separation mechanism 35c, and the like. The belt cleaning device (belt cleaner) 35 connects the brush roller 35a and the rubber blade 35b with the contact / separation mechanism 35c from the start of the copying operation to the end of the belt transfer at the rear end of the Y image (final color image). The brush roller 35a and the rubber blade 35b are separated from the intermediate transfer belt 29 at a predetermined timing by the contact / separation mechanism 35c.
To clean the intermediate transfer belt 29.

The paper transfer unit 36 includes a paper transfer bias roller 36a, a roller cleaning blade 36b, a contact / separation mechanism 36c, and the like. The paper transfer bias roller 36a is normally separated from the intermediate transfer belt 29. However, when the four-color superimposed image formed on the intermediate transfer belt 29 is collectively transferred onto the transfer paper, the paper transfer bias roller 36a contacts the paper transfer bias roller 36a. The paper transfer bias roller 36a is pressed by the separating mechanism 36c and abuts on the intermediate transfer belt 29, and a predetermined transfer bias voltage is applied to the paper transfer bias roller 36a from a high-voltage power supply to pass between the paper transfer bias roller 36a and the intermediate transfer belt 29. The four-color superimposed image on the intermediate transfer belt 29 is transferred to the transfer paper.

In this case, the transfer paper is transferred to the transfer paper cassette 37-37.
40, paper is fed to the registration roller 45 by one of the paper feed rollers 41 to 44, or is fed from the manual paper feed tray 46 to the registration roller 45 by the paper feed roller 41. The transfer paper is sent out at the timing when the leading end of the four-color superimposed image on the intermediate transfer belt 29 reaches the paper transfer position.

The manner of movement of the intermediate transfer belt 29 is as follows.
As the operation method after the belt transfer of the BK toner image of the color has been completed to the rear end portion, the following constant speed forward system, skip forward system, and reciprocating (quick return) system can be considered. A system or a system in which these are efficiently combined according to the copy size (in terms of copy speed or the like) is used.

1) -Constant speed forward movement method Even after the intermediate transfer belt 29 transfers the BK toner image, the forward movement continues at the constant speed. When the leading edge position of the BK image on the intermediate transfer belt 29 reaches the belt transfer position of the contact portion with the photosensitive drum 12 again, the leading end portion of the next C toner image is moved to the belt transfer position. An image is formed at appropriate timing. As a result, the C image is accurately transferred to the BK image and transferred onto the intermediate transfer belt 29 in a superimposed manner. Thereafter, the M image forming step and the Y image forming step are performed by the same operation, and a belt transfer image of four colors is obtained on the intermediate transfer belt 29. Following the step of performing the belt transfer of the Y toner image of the fourth color by the intermediate transfer belt 29, the four-color superimposed toner image is transferred onto the transfer paper as described above while moving forward as it is.

2) Skip Forward Movement When the transfer of the BK toner image is completed, the intermediate transfer belt 29 is separated from the photosensitive drum 12, skipped at a high speed in the forward movement direction, and moved by a predetermined amount. Return to forward speed. Thereafter, the intermediate transfer belt 29 comes into contact with the photosensitive drum 12 again. When the front end position of the BK image on the intermediate transfer belt 29 reaches the belt transfer position again, the photosensitive drum 12 is set to a timing such that the front end portion of the next C toner image comes to the belt transfer position. It is formed. as a result,
The C image is transferred to the belt while being superimposed exactly on the BK image. Thereafter, the M image forming step and the Y image forming step are performed by the same operation, and a belt transfer image of four colors is obtained on the intermediate transfer belt 29. The intermediate transfer belt 29 transfers the four-color superimposed toner image onto the transfer paper at the same forward speed following the step of performing the belt transfer of the fourth color Y toner image.

3) Reciprocating (Quick Return) Method When the transfer of the BK toner image is completed, the intermediate transfer belt 29 is separated from the photosensitive drum 12, stops the forward movement, and simultaneously returns in the reverse direction at a high speed. This return is stopped after the front end position of the BK image on the intermediate transfer belt 29 has passed the position corresponding to the belt transfer in the reverse direction, and further moved by a predetermined distance, and enters a standby state. Next, on the photosensitive drum 12 side, when the leading end of the C toner image reaches a predetermined position before the belt transfer position, the intermediate transfer belt 29 is started again in the forward movement direction, and comes into contact with the photosensitive drum 12 again. . Also in this case, the conditions are controlled so that the C image accurately overlaps the BK image on the intermediate transfer belt 29. Thereafter, the M image forming step and the Y image forming step are performed by the same operation, and a belt transfer image of four colors is obtained on the intermediate transfer belt 29. Following the belt transfer process of the Y toner image of the fourth color, the intermediate transfer belt 29 moves forward at the same speed without returning and transfers the four-color superimposed toner image on the transfer paper.

The transfer paper onto which the four-color superimposed toner image has been transferred from the intermediate transfer belt 29 in this manner is conveyed to the fixing unit 48 by the paper conveying unit 47 and is controlled to a predetermined temperature of the fixing unit 48. The toner image is melted and fixed by the fixing roller 48a and the pressure roller 48b, and is carried out to the copy tray 49 as a full color copy. Further, the photoreceptor belt 12 after the belt transfer is uniformly discharged by the pre-cleaning discharger 18 by the photoreceptor cleaning device 19, and the brush roller 19 a and the rubber blade 19 are removed.
The surface is cleaned by b, and the charge is uniformly removed by the charge removing lamp 20. The surface of the intermediate transfer belt 29 is cleaned by a cleaning unit 35 at a predetermined timing after the transfer of the final color Y toner image onto the transfer paper. At this time, the brush roller 35a and the rubber blade 3
5b is pressed against the intermediate transfer belt 29 by the contact / separation mechanism 35c.

At the time of repeat copying in which copying is continuously performed, the operation of the color scanner 1 and the image formation on the photosensitive drum 12 are started following the Y (fourth color) image forming process of the first sheet, and at a predetermined timing. The process proceeds to a second BK (first color) image forming process. Further, after the step of transferring the four-color superimposed image onto the first sheet of transfer paper in the intermediate transfer belt 29, the second sheet of the BK toner image is transferred to the area where the surface is cleaned by the cleaning device 35. 12 is transferred to the belt. Thereafter, the same operation as that of the first sheet is performed, and thereafter, the same operation is performed for each sheet.

The transfer paper cassettes 37 to 40 store transfer papers of various sizes, and are provided with paper feed rollers 41 to 44.
Is supplied to the registration roller 45 at a timing from a transfer paper cassette in which transfer paper of a size designated by an operation panel (not shown) is stored. The manual feed tray 46 is used to feed OHP paper, thick paper, or the like in the manual feed mode.

The above operation is a copy mode operation for obtaining a full-color copy of four colors.
When a copy is obtained in the color copy mode, the same operation as described above is performed for the number of colors and the number specified by the operation unit. Further, in the case of a single-color copy mode for obtaining a single-color copy, only the single-color developing device is in a developing operation (development of developer) until the predetermined number of copies are completed, and the intermediate transfer belt 29 is moved. The belt cleaning unit 35 is driven at a constant speed in the forward movement direction while being in contact with the photosensitive drum 12, and the belt cleaning unit 35 performs the copying operation while being kept in contact with the intermediate transfer belt 29.

FIG. 1 shows a circuit configuration of the first embodiment.
A control means 51 comprising a system control board having a built-in CPU and the like controls the entire color copying apparatus of the first embodiment. The system control board 51 takes in each key input signal from the operation unit 52 and causes the operation unit 52 to perform various displays. The editor 53 edits image data according to instructions from the system control board 51, and various peripheral devices 54 are controlled by the system control board 51. Document size detector 5
Reference numeral 5 denotes a size of the document on the document table 3, and a detection signal is input to the system control board 51, and a transfer paper size detector 5 is provided.
6 detects the size of each transfer sheet in the sheet feeding devices 37 to 40 and inputs the detection signal to the system control plate 51. The various detectors 57 perform various detections of the first embodiment, and input the detection signals to the system control board 51.

The polygon motor 15 has a system control board 51
The intermediate transfer belt drive motor control plate 58
Controls the intermediate transfer belt drive motor 59 in accordance with an instruction from the system control plate 51. The AC load control plate 60 is
A fixing heater for heating the fixing roller 48 a and other AC loads 61 are controlled in accordance with an instruction from the system control plate 51. The belt contact solenoid 62 is connected to the intermediate transfer belt 2.
The intermediate transfer belt 29 is moved toward and away from the photosensitive drum 12 by operating or disabling a contacting / separating mechanism for moving the photosensitive drum 9 to and from the photosensitive drum 12 in accordance with an instruction from the system control plate 51. The paper transfer roller contact solenoid 63 causes the paper transfer bias roller 36a to contact and separate from the intermediate transfer belt 29 by operating or disabling the contact / separation mechanism 63c according to an instruction from the system control plate 51.

The belt cleaner contact solenoid 64 moves the belt cleaner 35 toward and away from the intermediate transfer belt 29 by operating or disabling the contact / separation mechanism 35c in accordance with an instruction from the system control plate 51. The Bk developing sleeve motor 65, the C developing sleeve motor 66, the M developing sleeve motor 67, and the Y developing sleeve motor 68 are connected to the developing units 23 to 2 in accordance with an instruction from the system control plate 51.
The rotation of the developing sleeves 23a, 24a, 25a, and 26a is controlled. The high-voltage power supply 69 controls the charger 21 according to an instruction from the system control plate 51, and the various process loads 70 and the various drive loads 71 of the first embodiment are controlled by the system control plate 51.

FIG. 4 shows a circuit configuration of a portion from the color scanner 1 to the writing optical unit 11. The scanner control plate 72 controls the scanner motor 73 and outputs blue, green, and red image signals from the color CCD 10 including a color sensor to the image processing unit 74. The polygon synchronization detector 76 detects the laser beam from the fθ lens 16 outside the image area, and inputs a detection signal to a laser drive control plate 75. 13 is controlled.

FIGS. 5 to 7 show the operation flow of this embodiment. In this embodiment, for example, a reciprocating method is employed as a method of moving the intermediate transfer belt 29. The photosensitive drum 12 is uniformly charged, and a laser beam is applied only to a portion corresponding to an image to form a negative electrostatic latent image. The negative electrostatic latent image is developed only in a low potential portion. It is visualized as a toner image by development. Therefore, the non-image portion on the photosensitive drum 12 is slightly attenuated, but almost all of the charged electric charge remains. During the formation of a color image, for example, the portion between the rear end of the first color toner image and the front end of the second color toner image on the photosensitive drum 12 is also charged.

When the toner image on the photosensitive drum 12 is belt-transferred to the intermediate transfer belt 29, the photosensitive drum 12
The intermediate transfer belt 29 is rotated by contact with the intermediate transfer belt 29, but the intermediate transfer belt 29 is electrostatically attracted to the photosensitive drum 12 by a strong force due to the electric charge of the non-image portion on the photosensitive drum 12.
Then, for example, even when the belt transfer ends to the rear end of the first color toner image on the photosensitive drum 12, the intermediate transfer belt 29 is electrostatically attracted to the photosensitive drum 12 with a strong force.
The intermediate transfer belt 29 is separated from the photosensitive drum 12 and proceeds to the return operation in preparation for the belt transfer of the next second color toner image on the photosensitive drum 12, but the intermediate transfer belt 29 is electrostatically attracted to the photosensitive drum 12. At the time of the separating operation from the state, as described above, a large load variation is applied to the photosensitive drum 12 drive unit, and the image quality is reduced by the influence.

Therefore, in this embodiment, the intermediate transfer belt 2
9 is separated from the photosensitive drum 12, a predetermined non-imaging area after the rear end of the image portion on the photosensitive drum 12 is charged or has a low charge state of a predetermined value or less. When the toner reaches the transfer nip portion, the intermediate transfer belt 29 is separated from the photosensitive drum 12 to prevent the image quality from deteriorating. For example, the non-image forming area on the photosensitive drum 12 is 26, the charge is removed by light or corona discharge at a pre-transfer charge remover 28 comprising one or both of a light irradiation charge remover and a corona discharger at a position downstream of the developing position and upstream of the belt transfer position. Here, the transfer nip portion is a portion where the photosensitive drum 12 and the intermediate transfer belt 29 are in contact, and the transfer nip width LB is the width of the transfer nip portion in the rotation direction of the photosensitive drum 12 and the intermediate transfer belt 29.

The pre-transfer static elimination in which the image area on the photosensitive drum is neutralized between the developing area and the transfer area by the pre-transfer static eliminator is an electrophotographic image forming method in which normal positive / positive development is performed. The apparatus is used to remove the charge on the back surface of the toner to improve the transfer rate. However, in the image forming apparatus that performs the negative / positive reversal development as in the present embodiment, if the image area on the photosensitive drum 12 is neutralized by the pre-transfer static eliminator 28 between the developing area and the transfer area, the photosensitive area is reduced. Body drum 1
Disappearance of the charge on the background around the toner image 2 causes unstable toner adhesion and image disturbance, which is not preferable. Therefore, in the present embodiment, the pre-transfer static eliminator 28 eliminates the charge of the photosensitive drum 12 while avoiding the image area. Since the pre-transfer static eliminator 28 removes the charge after the photosensitive drum 12 has already passed through the developing device that performs the negative / positive reversal development, there is no toner adhesion stain on the low potential portion due to the static elimination of the photosensitive drum 12, There is an advantage that consideration of this problem is unnecessary.

The system control board 51 controls each load to start the above-described full-color copying operation in response to a copy start signal from the operation section 52 and to continuously repeat the number of copies set by the operation section 52. However, as shown in FIG. 5, first, in step 101, forward rotation of the intermediate transfer belt 29 is started, and in step 102, the area cleaned by the belt cleaner 35 on the intermediate transfer belt 29 has reached the belt transfer area. Judge whether or not.

The system control plate 51 is connected to the intermediate transfer belt 2
When the area cleaned by the belt cleaner 35 on the belt 9 reaches the belt transfer area, the process proceeds to step 103, where the forward rotation of the intermediate transfer belt 29 is stopped, and step 10
By detecting whether or not the transfer paper reference signal has come at 4, it is determined whether or not a predetermined timing for rotating the intermediate transfer belt 29 forward has come. When the transfer paper reference signal has come, the routine proceeds to step 105. The forward rotation of the intermediate transfer belt 29 is started.

Next, the system control board 51 executes step 1
In step 06, the belt contact solenoid 62 is turned on to bring the intermediate transfer belt 29 into contact with the photosensitive drum 12, and
At 07, it is determined whether or not it is time to perform the belt transfer of the Y toner image of the final color. If it is not time to perform the belt transfer of the final color Y toner image, the system control plate 51 determines in step 115 that the image (toner image) on the photosensitive drum 12
It is determined whether or not the rear end has passed the pre-transfer neutralizer 28,
When the rear end of the image on the photosensitive drum 12 has passed the pre-transfer static eliminator 28, the process proceeds to step 116, where the pre-transfer static eliminator 2
8 is turned on. Accordingly, the pre-transfer static eliminator 28 neutralizes a predetermined non-image forming area downstream of the rear end of the image on the photoconductor drum 12 in the rotation direction of the photoconductor drum 12 to lower its charging potential, and The start timing of the substantial separation operation from the intermediate transfer body 29 is after the predetermined non-image forming area on the photosensitive drum 12 is opposed to almost the entire area of the transfer nip width.

Next, the system control board 51 executes step 1
At 17, it is determined whether the pre-transfer static eliminator 28 has neutralized a predetermined non-image forming area having a width equal to or greater than the transfer nip width LB downstream of the rear end of the image on the photosensitive drum 12 in the rotation direction of the photosensitive drum 12. When it is determined that the pre-transfer static eliminator 28 has finished discharging the non-image forming area, the process proceeds to step 118, where the pre-transfer static eliminator 28 is turned off. Therefore, the end timing of the substantial separation operation between the photosensitive drum 12 and the intermediate transfer body 29 is
A predetermined non-image forming area on the photosensitive drum 12 is in a state of being opposed to almost the entire area of the transfer nip width.

Next, the system control board 51 executes step 1
At 19, it is determined whether or not the leading end of the non-image forming area on the photoconductive drum 12 which has been neutralized by the pre-transfer static eliminator 28 has passed through the transfer nip portion. When the leading end of the non-image forming area passes through the transfer nip, the belt contact solenoid 62 is turned off in step 120 to separate the intermediate transfer belt 29 from the photosensitive drum 12. Therefore, the pre-transfer static eliminator 28 on the photosensitive drum 12
The photosensitive drum 12 and the intermediate transfer body 29 are separated from each other at the timing when the non-image forming area where the charge has been removed becomes the transfer area (the area where the toner image is transferred).

Next, the system control board 51 executes step 1
In step 21, the forward rotation of the intermediate transfer belt 29 is stopped, and in step 122, a high-speed return operation by reverse rotation of the intermediate transfer belt 29 is started. Then, the system control board 51
In step 123, it is determined whether the intermediate transfer belt 29 has returned to a predetermined position where the superimposition transfer of the next color toner image is started, and the intermediate transfer belt 29 starts superimposition transfer of the next color toner image. When the process returns to the predetermined position, the process proceeds to step 124, where the high-speed return operation by the reverse rotation of the intermediate transfer belt 29 is stopped.
Return to

Accordingly, the pre-transfer static eliminator 28 removes the charge potential of a predetermined non-image forming area between the image forming areas (between the toner images of the respective colors) on the photosensitive drum 12 upstream of the transfer section area. ,
That is, the photosensitive drum 1 is located between the developing area and the transfer section area.
2 at a predetermined timing after the trailing end of the toner image on the photosensitive drum 12 has passed the charged potential of the photosensitive drum 12 and until the next color toner image on the photosensitive drum 12 arrives, and a predetermined non-operation is performed. The charging potential of the image area is reduced.

Further, the system control board 51 performs step 1
If it is determined in 07 that it is time to perform the belt transfer of the Y toner image of the final color, the process proceeds to step 108 to determine whether or not the belt transfer has been completed. Contact solenoid 6
4 to turn on the belt cleaner 35 and the intermediate transfer belt 2
Contact 9

Next, the system control board 51 executes step 1
At 10, it is determined whether or not the leading end of the image on the intermediate transfer belt 29 has advanced to a predetermined position on the upstream side in the rotation direction of the intermediate transfer belt 29 from the paper transfer unit 36. When the unit 36 has advanced to a predetermined position on the upstream side in the rotation direction of the intermediate transfer belt 29, the paper transfer roller contact solenoid 63 is turned on in step 111 to bring the paper transfer bias roller 36 a into contact with the intermediate transfer belt 29.

Next, the system control board 51 executes step 1
In step 12, it is determined whether the image on the intermediate transfer belt 29 has been transferred to the transfer sheet to the rear end. If the image on the intermediate transfer belt 29 has been transferred to the transfer sheet to the rear end, step 1 is executed.
At 13, the paper transfer roller contact solenoid 63 is turned off to separate the paper transfer bias roller 36 a from the intermediate transfer belt 29. Next, the system control board 51 executes step 11
At 4, it is determined whether or not the copying operation is a final copying operation (final copy) for the same document.

If the copying operation is not the final copying operation for the same original, the system control board 51
As shown in FIG.
5 determines whether the intermediate transfer belt 29 has been cleaned of all remaining transfer areas up to a position corresponding to the rear end of the image, and the belt cleaner 35 moves the intermediate transfer belt 29 to a position corresponding to the rear end of the image. When cleaning of the entire area of the belt contact solenoid 62 is completed in step 131,
Is turned off to separate the intermediate transfer belt 29 from the photosensitive drum 12, and in step 132, the belt cleaner contact solenoid 64 is turned off to separate the belt cleaner 35 from the intermediate transfer belt 29.

Next, the system control board 51 executes step 1
At 33, the forward rotation of the intermediate transfer belt 29 is stopped, and at step 134, a high-speed return operation by reverse rotation of the intermediate transfer belt 29 is started. Then, the system control board 51
Determines in step 135 whether the cleaning area of the belt cleaner 35 has returned to the next image area on the intermediate transfer belt 29 by a predetermined amount, and the cleaning area of the belt cleaner 35 When returning to the next image area by a predetermined amount, the high-speed return operation by reverse rotation of the intermediate transfer belt 29 is stopped in step 136, and the process returns to step 104.

Further, the system control board 51 executes step 1
If it is determined in step 14 that the copying operation is the final copying operation for the same document, the process proceeds to step 125, as shown in FIG. 6, to determine whether the belt cleaner 35 has cleaned the intermediate transfer belt 29 by a predetermined amount corresponding to one rotation or more. If it is determined that the belt cleaner 35 has cleaned the intermediate transfer belt 29 by a predetermined amount corresponding to one turn or more, the belt contact solenoid 62 is turned off in step 126 to separate the intermediate transfer belt 29 from the photosensitive drum 12. Next, the system control plate 51 stops the forward rotation of the intermediate transfer belt 29 in step 127, and determines in step 128 whether or not a predetermined time required for calming the floating toner in the belt cleaner 35 has elapsed. When the predetermined time has elapsed, in step 129, the belt cleaner contact solenoid 64 is turned off to separate the belt cleaner 35 from the intermediate transfer belt 29.

In the first embodiment, the charging potential of a predetermined non-image forming area on the photosensitive drum 12 is lowered so that the predetermined non-image forming area becomes intermediate with the photosensitive drum 12 at the timing of becoming the transfer area. Since the transfer member 29 is separated, the electrostatic attraction force between the photosensitive drum 12 and the intermediate transfer member 29 is lost during this separation operation, and a driving unit including a photosensitive drum drive motor for driving the photosensitive drum 12 is provided. Load fluctuation is eliminated. Therefore, it is possible to prevent the speed of the photosensitive drum 12 from fluctuating, and to prevent the image quality from deteriorating due to the displacement or banding of the color image due to the expansion and contraction of the image, and the disturbance of the image.

The charge potential of a predetermined non-image forming area between the respective image forming areas on the photosensitive drum 12 is eliminated by the pre-transfer static eliminator 28 on the upstream side of the transfer section area. , The adverse effect during the separation operation can be reliably prevented without dealing with unnecessary toner contamination on the non-image forming area where the charge is to be removed. In addition, the pre-transfer static eliminator 28
Indicates that the charged potential of the photosensitive drum 12 passes between the developing area and the transfer section area after the rear end of the toner image on the photosensitive drum 12 passes and until the next toner image on the photosensitive drum 12 reaches In this case, the charge is removed at a predetermined timing to lower the charged potential of a predetermined non-image forming area, so that the object can be reliably achieved without disturbing the toner image on the photosensitive drum 12.

Further, since the length of the non-image forming area on the photosensitive drum 12 to be neutralized by the pre-transfer neutralizer 28 is at least equal to or greater than the transfer nip width, the photosensitive drum 12 and the intermediate transfer body 2
9, the electrostatic attraction force at the time of the separating operation from the photosensitive drum 9 is surely eliminated, and the load fluctuation of the photosensitive drum drive motor is eliminated, so that the image quality can be prevented from lowering. Further, the start timing of the substantial separation operation between the photosensitive drum 12 and the intermediate transfer body 29 is
Since the predetermined non-image forming area on the photosensitive drum 12 is substantially equal to the entire area of the transfer nip width and thereafter, the electrostatic attraction force at the start of the separating operation between the photosensitive drum 12 and the intermediate transfer body 29 is reduced. As a result, the load on the photosensitive drum driving motor does not fluctuate, thereby preventing a decrease in image quality.

Further, the photosensitive drum 12 and the intermediate transfer member 29
The end timing of the substantial separation operation is such that the predetermined non-image forming area on the photosensitive drum 12 is in a state of being opposed to almost the entire area of the transfer nip width. During this period, the electrostatic attraction force is surely lost until the separation operation is completed, and the load on the photosensitive drum drive motor does not fluctuate. Further, by using a light irradiator that removes electricity by irradiating the photosensitive drum 12 with light as the pre-transfer static eliminator 28, the object can be achieved by the simple and reliable pre-transfer static eliminator 28. Further, by using a corona discharger as the pre-transfer static eliminator 28, the object can be achieved by a simple and reliable pre-transfer static eliminator 28.

The second embodiment of the present invention is an embodiment of the fourth aspect of the present invention. In the first embodiment, the pre-transfer static eliminator 28 is omitted, and the system control plate 51 performs charging as a charging means. The photosensitive drum 1 as shown in the broken line in FIG.
The predetermined non-image forming area is neutralized by temporarily turning off a part of the non-image forming area between the preceding image forming area and the next image forming area. The third embodiment of the present invention is an embodiment of the present invention described in claim 5. In the first embodiment, the pre-transfer static eliminator 28 is omitted, and the system control plate 51 uses the writing optical system as an exposure unit. The photosensitive drum 1 is attached to the unit 11 as shown by the broken line in FIG.
The predetermined non-image forming area is neutralized by temporarily erasing the charge on the photosensitive drum 12 in a part of the non-image forming area between the preceding image forming area and the next image forming area. It is something to do.

In the second embodiment and the third embodiment, the object can be achieved by adding the operation control of the existing ones 21 and 11 without providing a new static eliminator, and the cost is not increased. Has the advantage of achieving its purpose. In the second and third embodiments of the present invention, the photosensitive drum 12 is provided with a charging device upstream of the developing devices 23 to 26 for performing negative / positive reversal development in the rotation direction. 21 and the writing optical unit 11, a low potential portion is formed. Therefore, when the low potential portion area passes through the developing devices 23 to 26, the system control plate 51
The charging device 21 and the writing optical unit 11 are operated such that the developing sleeves 23a to 26a do not operate when the ears are cut off.
Of the low potential portion (the above-mentioned predetermined non-image forming area) by the developing sleeve 2 and the developing sleeve 2 controlled by the developing sleeve motors 65 to 68
The timing control of the ear cutting of 3a to 26a is performed. For this reason, unnecessary development of the low potential portion on the photosensitive drum 12 can be prevented, so that an increase in toner consumption can be prevented, and consideration of problems such as soiling of the photosensitive drum 12 becomes unnecessary.

The system control plate 51 separates the intermediate transfer member 29 from the photosensitive drum 12 similarly to the first embodiment, that is, the photosensitive drum 12 and the intermediate transfer member 29.
Is started when the predetermined non-image forming area on the photosensitive drum 12 is substantially equal to the entire area of the transfer nip width. The end timing of the substantial separating operation is set such that a predetermined non-image forming area on the photosensitive drum 12 is opposed to almost the entire area of the transfer nip width. Note that the present invention is not limited to the above-described embodiment, and can be similarly applied to an image forming apparatus different from the above-described embodiment.

[0087]

As described above, according to the first aspect of the present invention, after the photosensitive member is rotated and uniformly charged by the charging means, the photosensitive member is irradiated with light by the exposure means to form a negative electrostatic latent image thereon. The electrostatic latent image is formed and visualized as a toner image by reversal development by a developing unit, and the toner image on the photoconductor is transferred to the intermediate transfer body while the intermediate transfer body is brought into contact with the photoconductor and rotated. In an image forming apparatus for transferring and separating the photosensitive member and the intermediate transfer member after the transfer of the toner image in a predetermined image forming region on the photosensitive member, a charging potential of a predetermined non-image forming region on the photosensitive member Means for separating the photosensitive member and the intermediate transfer member at a timing when the predetermined non-image forming region becomes the transfer portion region, so that the distance between the photosensitive member and the intermediate transfer member during the separating operation is provided. The electrostatic attraction force is lost and the photoconductor is driven. Load variations of the drive unit is eliminated. Therefore, it is possible to prevent the speed fluctuation of the photoconductor, and to prevent the image quality from deteriorating due to positional displacement, banding, and image disturbance due to expansion and contraction of the image.

According to the second aspect of the present invention, in the image forming apparatus according to the first aspect, the charging potential of a predetermined non-imaging area between the image forming areas on the photosensitive member is set to an upstream side of the transfer section area. Means for lowering the charged potential of the non-image forming area by eliminating the electric charges at the non-image forming area. .

According to the third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the means for lowering the charged potential of the non-image forming area is provided between the developing area and the transfer section area. The charge is removed from the photoconductor at a predetermined timing after the trailing end of the toner image on the photoconductor passes through the rear end of the toner image and before the next toner image on the photoconductor arrives. Since the charged potential in the image forming area is reduced, the object can be reliably achieved without disturbing the toner image on the photoconductor.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the charging unit is configured to perform non-imaging between a preceding image forming area and a next image forming area on the photosensitive member. Since the predetermined non-imaging area is temporarily turned off by partially turning off the area, the existing one can be used, and there is an advantage that the object can be surely achieved without increasing the cost.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the non-production between the preceding image forming area and the next image forming area on the photoconductor by the exposure means is performed. Since the charge on the photoconductor is temporarily erased and erased in the predetermined non-image forming area in a part of the image area, the existing one can be used, and the purpose can be reliably achieved without increasing the cost. There are benefits that can be achieved.

According to the invention described in claim 6, according to claim 1,
In the image forming apparatus described in 2, 3, 4 or 5, the length of the predetermined non-image forming area is at least equal to or greater than the transfer nip width, so that the electrostatic attraction force at the time of the separating operation between the photosensitive member and the intermediate transfer member. Is reliably eliminated, and the load of driving the photosensitive member is not changed, thereby preventing the image quality from deteriorating.

According to the invention of claim 7, according to claim 1,
The image forming apparatus according to 2, 3, 4, 5, or 6,
Since the start timing of the substantial separation operation between the photosensitive member and the intermediate transfer member is set to be after the predetermined non-imaging area on the photosensitive member is substantially opposed to the entire area of the transfer nip width, The electrostatic attraction force at the start of the separation operation between the photoconductor and the intermediate transfer body is reliably eliminated, and the load fluctuation of the photoconductor driving is eliminated, thereby preventing the image quality from deteriorating.

According to the invention described in claim 8, according to claim 1,
The image forming apparatus according to 2, 3, 4, 5, or 6,
Since the end timing of the substantial separation operation between the photoconductor and the intermediate transfer body is such that a predetermined non-imaging area on the photoconductor is opposed to substantially the entire area of the transfer nip width, The electrostatic attraction between the intermediate transfer member and the intermediate transfer member is reliably eliminated until the separation operation is completed, and the load on the photosensitive member is not changed.

According to the ninth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, the developing means is developed so that toner does not adhere to a predetermined non-image forming area on the photosensitive member. Since the operation is disabled, the object can be achieved without unnecessary consumption of toner or contamination of the photoconductor.

According to the tenth aspect, the second aspect is provided.
In the image forming apparatus according to the third or third aspect, since the static eliminator is a light irradiation static eliminator that eliminates static electricity by irradiating the photosensitive member with light, the object can be achieved by a simple and reliable static eliminator.

According to the eleventh aspect, according to the second aspect,
In the image forming apparatus according to the third aspect, since the static elimination unit is a corona discharger, the object can be achieved by a simple and reliable static elimination unit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a part of a circuit configuration according to a first embodiment of the present invention.

FIG. 2 is a sectional view schematically showing the first embodiment.

FIG. 3 is an enlarged sectional view showing a part of the first embodiment.

FIG. 4 is a block diagram showing a circuit configuration of a portion from a color scanner to a writing optical unit in the first embodiment.

FIG. 5 is a flowchart showing a part of the operation flow of the first embodiment.

FIG. 6 is a flowchart showing another part of the operation flow of the first embodiment.

FIG. 7 is a flowchart showing another part of the operation flow of the first embodiment.

FIG. 8 is a timing chart showing the operation timing of the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Writing optical unit 12 Photoreceptor drum 21 Charger 23-26 Developing device 28 Pre-transfer static eliminator 29 Intermediate transfer member 35 Belt cleaner 36 Paper transfer unit 51 System control plate 59 Belt drive motor 63 Paper transfer roller contact solenoid 64 Belt cleaner contact Solenoid 65-68 Developing sleeve motor

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-43770 (JP, A) JP-A-3-192280 (JP, A) JP-A-5-165383 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G03G 15/00 G03G 15/01 G03G 15/16 G03G 21/00 G03G 21/06-21/08 G03G 21/14

Claims (11)

(57) [Claims] After the photosensitive member is rotated and uniformly charged by a charging means, a negative electrostatic latent image is formed on the photosensitive member by irradiating the photosensitive member with light by an exposure means, and the electrostatic latent image is reversely developed by a developing means. The toner image on the photoreceptor is transferred to the intermediate transfer body while the intermediate transfer body is brought into contact with the photoreceptor and rotated, and a predetermined image forming area on the photoreceptor is formed. In the image forming apparatus for separating the photoconductor and the intermediate transfer body after the transfer of the toner image, the charging potential of a predetermined non-image forming area on the photoconductor is reduced to make the predetermined non-image forming area a transfer unit. An image forming apparatus comprising: means for separating the photosensitive member and the intermediate transfer member at a timing when the region becomes an area. 2. The image forming apparatus according to claim 1, wherein the charge potential of a predetermined non-image forming area between the image forming areas on the photoreceptor is removed on the upstream side of a transfer section area. An image forming apparatus comprising: means for lowering a charged potential of an image forming area. 3. An image forming apparatus according to claim 1, wherein said means for lowering the charging potential of said non-image forming area is provided between a developing area and a transfer section area, and said charging potential of said photoconductor is reduced. At a predetermined timing after the rear end of the toner image on the photoconductor has passed and until the next toner image on the photoconductor arrives, to lower the charging potential of the predetermined non-image forming area. An image forming apparatus. 4. An image forming apparatus according to claim 1, wherein said charging means is temporarily provided in a part of a non-image forming area between a preceding image forming area and a next image forming area on said photosensitive member. An image forming apparatus, wherein the predetermined non-image forming area is turned off to remove electricity. 5. An image forming apparatus according to claim 1, wherein said exposure means temporarily covers a part of a non-image forming area between a preceding image forming area and a next image forming area on said photosensitive member. An image forming apparatus for erasing the charge on the photoreceptor to eliminate the charge in the predetermined non-image forming area. 6. An image forming apparatus according to claim 1, wherein said predetermined non-image forming area has a length at least equal to or greater than a transfer nip width. 7. The image forming apparatus according to claim 1, wherein the start timing of the substantial separating operation between the photosensitive member and the intermediate transfer member is set on the photosensitive member. An image forming apparatus characterized in that a predetermined non-image forming area is set to be after a time when a predetermined non-image forming area is opposed to a substantially entire area of a transfer nip width. 8. The image forming apparatus according to claim 1, wherein the end timing of the substantial separation operation between the photosensitive member and the intermediate transfer member is determined by setting the end timing on the photosensitive member. An image forming apparatus, wherein a predetermined non-image forming area is in a state of being opposed to almost the entire area of the transfer nip width. 9. An image forming apparatus according to claim 4, wherein said developing means is deactivated so that toner does not adhere to a predetermined non-image forming area on said photosensitive member. Image forming apparatus. 10. An image forming apparatus according to claim 2, wherein said static eliminator is a light irradiator for irradiating said photosensitive member with light. 11. An image forming apparatus according to claim 2, wherein said discharging means is a corona discharger.