JP2000155516A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the irregular gradation steps in an image caused by the irregular drive of an image forming body by setting the linear velocity of the image forming body and that of an intermediate transfer body to specified values, respectively, and setting a relative velocity difference between the image forming body and the intermediate transfer body within a specified range at least at the time of forming a toner image on a front surface. SOLUTION: When an intermediate transfer belt 14a is rotated with abutting pressure by a photoreceptor drum 10 and they are rotated at the equal linear velocity, the function of the belt 14a as a damper is lowered, and slip is easily caused between them. As a result, the gradation steps in the image is caused by the irregular drive of the drum 10. Assuming that the linear velocity of the drum 10 functioning as the image forming body is Vp (mm/sec) and the linear velocity of the belt 14a functioning as the intermediate transfer body is Vb (mm/sec), the relative velocity difference (%) between the drum 10 and the belt 14a is set to the range shown by an expression; 0.015<=|(Vb-Vp)/ Vp|<=0.05 at least at the time of forming the toner image on the front surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to copying in which a charging means, an image writing means and a developing means are arranged around an image forming body to transfer and fix a toner image formed on the image forming body onto a transfer material. More particularly, the present invention relates to an image forming apparatus capable of forming an image on both sides of a transfer material.

[0002]

2. Description of the Related Art Conventionally, in double-sided image formation, an image on one side formed on an image forming body is transferred and fixed on a transfer material, and this is temporarily stored in a double-sided reversal feeding device and formed again. A method has been adopted in which a transfer material is fed from a two-sided reversing feed device in synchronization with an image formed on a body, and an image on the other surface is transferred and fixed onto the transfer material.

In this double-sided image forming apparatus, as described above,
The transfer of the transfer material, such as feeding to the two-sided reversing feed device or passing through the fixing device twice, is performed, so that the reliability of transfer of the transfer material is low, causing jams and wrinkles of the transfer material. .

On the other hand, JP-B-49-37538 and JP-B-54-28740, and JP-A-1-44457.
Japanese Patent Application Laid-Open Publication No. 4-214576 and the like propose a method in which a toner image is formed on both surfaces of a transfer material using an image forming body and an intermediate transfer body, and then fixed once.

Further, the present inventors have arranged a plurality of sets of toner image forming means including a charging means, an image writing means, a developing means, etc. around a photosensitive drum (image forming body), and provided on the photosensitive drum. After the formed superimposed color toner image is once transferred to the belt-shaped intermediate transfer body by the first transfer means, the superimposed color toner image is formed again on the photoconductor drum, and the toner on the photoconductor drum is formed. The transfer material fed in time with the image and the toner image on the intermediate transfer body is charged by the transfer material charging means and adsorbed on the intermediate transfer body,
On both sides of the transfer material conveyed by the intermediate transfer body,
The toner image on the photosensitive drum is transferred as a front image by a second transfer unit (using the same one as the first transfer unit), and the toner image on the intermediate transfer body is transferred as a back image by a third transfer unit. Fixing device (fixing means)
The curvature of the roller member provided on the side and stretching the intermediate transfer member,
And an image forming apparatus and an image forming method for separating a transfer material from an intermediate transfer body by static elimination by a transfer material separating unit provided as necessary, and fixing a toner image on the transfer material by a fixing device to form a double-sided color image Is disclosed in JP-A-9-25849.
No. 2 and JP-A-9-258516.

[0006]

However, the toner images on the front and back sides of the image forming body (photosensitive drum) and the belt-like intermediate transfer body (intermediate transfer belt) are transferred onto a transfer material to form a double-sided image. In a double-sided image forming apparatus for forming
The intermediate transfer belt, which is disposed in contact with the photosensitive drum, serves as a damper (brake) that attenuates, due to the contact pressure, vibration that is originally generated when the photosensitive drum rotates and causes drive unevenness. However, when both are rotated at the same linear speed, the tension (contact pressure) of the intermediate transfer belt on the photosensitive drum is weakened, the role as a damper is weakened, and uneven driving of the photosensitive drum is amplified. There is a problem that unevenness of the image occurs due to uneven driving of the photosensitive drum. In particular, at the time of surface image formation, since the transfer material is interposed between the photosensitive drum and the intermediate transfer belt,
The contact pressure of the intermediate transfer belt on the photosensitive drum becomes weaker, the role of the intermediate transfer belt as a damper becomes weaker, slippage easily occurs between the two, and image unevenness due to uneven driving of the photosensitive drum is reduced. The problem that the occurrence becomes remarkable occurs.

[0007] The present invention solves the above-mentioned problems, and prevents the occurrence of uneven image steps caused by uneven driving of the image forming member when forming a double-sided image using the intermediate transfer member in contact with the image forming member. It is an object to provide an image forming apparatus.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming body, charging means for charging the image forming body, image writing means for forming an image writing latent image on the charged image forming body,
A developing unit that develops a latent image formed on the image forming body to form a toner image transfers a toner image on the image forming body, and a toner image on the image forming body. An endless belt-shaped intermediate transfer body that carries the toner image on the surface and conveys a transfer material; a first transfer unit that transfers the toner image on the image forming body to the intermediate transfer body; An image forming apparatus comprising: a second transfer unit that transfers a toner image on a formed body to a front surface of the transfer material; and a third transfer unit that transfers a toner image on the intermediate transfer body to a back surface of the transfer material. Wherein the linear velocity of the image forming body is V
p (mm / sec), and the linear velocity of the intermediate transfer member is Vb
(Mm / sec), at least during formation of a toner image on the surface, the relative speed difference (%) between the image forming body and the intermediate transfer body is 0.015 ≦ | (Vb−Vp) / Vp | 0.05 is achieved by an image forming apparatus (first invention).

Further, the object is to provide an image forming body, charging means for charging the image forming body, image writing means for forming an image writing latent image on the charged image forming body, and forming on the image forming body. Developing means for developing the latent image formed to form a toner image, means for forming a toner image on the image forming body,
The toner image on the image forming body is transferred, the transferred toner image is carried on the surface, and an endless belt-shaped intermediate transfer body that conveys a transfer material, and the toner image on the image forming body is A first transfer unit for transferring the toner image on the transfer member, and a second transfer unit for transferring the toner image on the image forming member to the surface of the transfer material
And a third transfer unit for transferring the toner image on the intermediate transfer body to the back surface of the transfer material, wherein the linear speed of the image formation body or the intermediate transfer body is variable. The second aspect of the present invention is achieved by an image forming apparatus that expands and contracts a toner image formed on the image forming body according to a change in a linear velocity of the image forming body or the intermediate transfer body (second aspect). invention).

[0010]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. In the following description of the embodiment, the surface of the transfer material on the side facing the image forming body in the transfer area is called the front surface, and the other surface of the transfer material, that is, the surface of the transfer material on the side facing the intermediate transfer body is called the back surface. The image transferred to the front surface of the transfer material is called a front image, and the image transferred to the back surface of the transfer material is called a back image.

An image forming process and each mechanism of an embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a sectional configuration view of a color image forming apparatus showing an embodiment of the image forming apparatus according to the present invention, FIG. 2 is a side sectional view of the image forming body of FIG. 1, and FIG. FIG. 3A is a diagram illustrating a toner image forming state in the image forming apparatus according to the present invention, and FIG. 3A is a diagram illustrating a toner image forming state when a back surface image formed on an image forming body is transferred onto an intermediate transfer body. FIG. 3B is a diagram illustrating a toner image forming state when a front surface image is formed on an image forming body in synchronization with a back side image on the intermediate transfer body.
FIG. 4C is a diagram illustrating double-sided image formation on a transfer material.

In FIG. 1, reference numeral 10 denotes a photosensitive drum as an image forming body; 11, a scorotron charger as charging means for each color; 12, an exposure optical system as image writing means for each color; The developing device 14a is an intermediate transfer belt which is an intermediate transfer member, and 14c is a first and a second transfer belt.
14g, a backside transfer unit as a third transfer unit, 14m, a neutralizer as a neutralization unit, and 150g.
Is a paper charger which is a transfer material charging means, 14h is a paper separation AC static eliminator which is a transfer material separating means, 160 is a conveying section having a separation claw 210 which is a claw member and a spur 162 which is a spur member, and 17 is a fixing member. It is a fixing device as a means. The image forming process member as described above is used in the image forming process of the image forming apparatus according to the present invention.

Hereinafter, each process member will be described.

The photosensitive drum 10, which is an image forming body, has a transparent conductive layer, a, on the outer periphery of a cylindrical base formed of a transparent member such as optical glass or transparent acrylic resin.
A photosensitive layer, such as an Si layer or an organic photosensitive layer (OPC), formed by an image forming body driving motor M2 (see FIG. 4) in a clockwise direction indicated by an arrow in FIG. 1 with the conductive layer grounded. , For example, at a linear speed of 300 mm / sec.

The photosensitive drum 10, as shown in FIG.
Flange members 10A and 1A at both ends for engaging and fixing it
The gear G integrated with the flange member 10B is supported by the bearings B1 and B2 fitted into the drum body 0B and supported rotatably by the drum shaft 30 erected and fixed to the apparatus main body. When driven by meshing with the drive gear, it is rotated at a constant speed in a predetermined direction.

A scorotron charger 11, which is a charging unit for each color, an exposure optical system 12, which is an image writing unit for each color, and a developing unit 13, which is a developing unit for each color, form a set of yellow (Y) ), Magenta (M), cyan (C), and black (K) are provided for the image forming process, and four sets are provided.
With respect to the 0 rotation direction, they are arranged in the order of Y, M, C, and K.

The scorotron charger 11, which is a charging means for each color, has a control grid maintained at a predetermined potential and a discharge electrode 11a composed of, for example, a sawtooth electrode, and faces the photosensitive layer of the photosensitive drum 10. And installed
The charging operation (in the present embodiment, negative charging) is performed by corona discharge having the same polarity as that of the toner.
A uniform potential is given to 0. As the discharge electrode 11a, a wire electrode or a needle electrode may be used.

Exposure optical system 1 as image writing means for each color
2 indicates that the exposure position on the photosensitive drum 10 is the photosensitive drum 1 with respect to the scorotron charger 11 for each color described above.
It is arranged inside the photoconductor drum 10 so as to be located on the downstream side in the rotation direction of 0. As shown in FIG. 2, each exposure optical system 12 includes a plurality of LEDs (light emitting diodes) as light emitting elements of image exposure light (image writing light) arranged in the main scanning direction in parallel with the drum axis 30. Linear exposure elements 12a arranged in an array, and a light converging light transmitter (trade name: Selfoc lens array) 12b as an imaging element
And a lens holder 12c, and is attached to the holding member 20. The holding member 20 has a transfer simultaneous exposure device 12d in addition to the exposure optical system 12 for each color.
The uniform exposure device 12e is attached to the photosensitive drum 10, and the uniform exposure device 12e is housed inside the light-transmitting substrate of the photosensitive drum 10. The exposure optical system 12 for each color writes an image on the photosensitive layer of the photosensitive drum 10 from the back surface in accordance with the image data of each color read by a separate image reading device and stored in the memory, and the image is statically placed on the photosensitive drum 10. An electrostatic latent image is formed. Exposure element 12
As a, besides LED, FL (phosphor emission), EL
(Electroluminescence), PL (plasma discharge)
It is also possible to use a plurality of light emitting elements such as those arranged in an array. The emission wavelength of the light-emitting element for the image exposure light (image writing light) is usually in the range of 780 to 900 nm, which is highly transparent to the Y, M, and C toners.
In this embodiment, since the image is written from the back side, the wavelength may be shorter than 400 to 780 nm, which does not sufficiently transmit the color toner. Further, since 80% or more of the image exposure light is absorbed by the photosensitive layer of the photosensitive drum 10, the influence of the reflection and absorption by the color toner on the surface of the photosensitive drum 10 can be neglected. Generally, the development order of the color toner is the toner image or the developing device 1.
The order of Y, M, C, and K is preferable from the relationship of color mixture to 3.
In FIG. 2, WA is a light emitting element (LE) for image exposure light.
D).

The developing device 13 as a developing means for each color keeps a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 and rotates in a forward direction with respect to the rotation direction of the photosensitive drum 10, for example, 0.5 to 1 mm in thickness. And a developing casing 131 formed of a cylindrical nonmagnetic stainless steel or aluminum material having an outer diameter of 15 to 25 mm, and a developing casing 138. Inside the developing casing 138, yellow (Y) and magenta ( M), cyan (C) and black (K) one-component or two-component developers. Each developing unit 13
Is maintained in a non-contact state with the photosensitive drum 10 with a predetermined gap, for example, 100 to 500 μm, by an abutting roller (not shown), and applies a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeve 131. By doing
Non-contact reversal development is performed to form a toner image on the photosensitive drum 10.

The intermediate transfer belt 14a, which is an intermediate transfer member, has a volume resistivity of 10 ⁸ to 10 ¹⁶ Ω · cm, preferably 10 ⁹
It is an endless belt of 〜１０10 ¹² Ωcm, for example, modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, a thickness of 0.1 to 0.1 to which a conductive material is dispersed in engineering plastic such as nylon alloy This is a seamless belt having a two-layer structure in which a 1.0-mm semiconductive film substrate is coated with a fluorine coating having a thickness of 5 to 50 μm, preferably as a toner filming preventing layer. In addition, as the base of the intermediate transfer belt 14a, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber or the like can be used. The intermediate transfer belt 14a includes a driving roller 1 that is a roller member.
4d, a ground roller 14j, a driven roller 14e, a guide roller 14f, and a tension roller 14i.
It is rotated counterclockwise as indicated by the arrow in FIG. The guide roller 14f, the driven roller 14e, the ground roller 14j, and the drive roller 14d are fixedly rotated, and the tension roller 14i is movably supported and rotated by the elastic force of a spring (not shown). The intermediate transfer member drive motor M1 (FIG. 4)
), The driving roller 14d is rotated, and the intermediate transfer belt 14a is driven.
The intermediate transfer belt 14a is rotated at a linear speed of m / sec. The rotation of the intermediate transfer belt 14a causes the ground roller 14j, the driven roller 14e, the guide roller 14f, and the tension roller 14i to be driven and rotated. Belt slack of the rotating intermediate transfer belt 14a is tensioned by the tension roller 14i. The recording paper P serving as a transfer material is located at a position where the intermediate transfer belt 14a is stretched around the driven roller 14e.
Is supplied and transported by the intermediate transfer belt 14a. Intermediate transfer belt 14 stretched around drive roller 14d
The recording paper P is separated from the intermediate transfer belt 14a at the curvature section KT at the end of the fixing device 17 on the side of a.

The transfer device 14c as the first or second transfer means is a corona discharge device provided to face the photosensitive drum 10 with the intermediate transfer belt 14a interposed therebetween. Transfer area 14 between
b is formed. A DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied to the transfer device 14c, and the toner image on the photosensitive drum 10 is transferred to the intermediate transfer belt 1.
4a or onto the surface of the recording paper P as a transfer material.

The back transfer device 14g, which is the third transfer means, is preferably constituted by a corona discharger, and is driven by the transfer device 14c downstream of the transfer device 14c and upstream of the drive roller 14d in the rotation direction of the intermediate transfer belt 14a. Roller 14d
And a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied to the intermediate transfer belt 14a. Is transferred to the back surface of the recording paper P.

The static eliminator 14m, which is a static eliminator, is constituted by a corona discharger.
In the movement direction, an AC voltage, which is provided in parallel with the transfer device 14c on the downstream side of the transfer device 14c as the first and second transfer means and in which a DC voltage of the same polarity or opposite polarity to the toner is superimposed, The charge of the intermediate transfer belt 14a which is applied and charged by the voltage application of the transfer device 14c is removed.

The paper charger 150, which is a transfer material charging means, is preferably constituted by a corona discharger, provided opposite the driven roller 14e, which is grounded across the intermediate transfer belt 14a, and has the same polarity as the toner (this embodiment). (In the embodiment, negative polarity) is applied, and the recording paper P is charged and attracted to the intermediate transfer belt 14a. In addition to the corona discharger, a paper charging brush or a paper charging roller that can abut and release the intermediate transfer belt 14a can be used as the paper charger 150.

Paper separation AC neutralizer 1 as transfer material separating means
Reference numeral 4h denotes a driving roller 14 which is preferably constituted by a corona discharger, and which is grounded to the end of the intermediate transfer belt 14a on the side of the fixing device 17 as required.
d, and an AC voltage obtained by superimposing a DC voltage of the same polarity or opposite polarity to the toner is applied as necessary.
The recording paper P conveyed by the intermediate transfer belt 14a is discharged and separated from the intermediate transfer belt 14a.

The transport section 160 includes a separation claw 210 as a claw member.
And a spur member 162 serving as a spur member. The spur member 162 is provided between the fixing device 17 and the curvature portion KT at the end of the intermediate transfer belt 14a on the fixing device 17 side. The transport unit 160 includes the fixing device 1
7, the intermediate transfer belt 14a is deformed, the toner image carried on the intermediate transfer belt 14a tends to be fused, and the transfer is difficult.
4a is prevented from sticking to the toner.

The separation claw 210, which is a claw member, is close to the curvature portion KT of the intermediate transfer belt 14a.
Is fixed to the support shaft 221 at a predetermined interval, preferably 0.1 to 2.0 mm, and when the recording paper P is separated from the intermediate transfer belt 14a, the intermediate transfer belt 1
The leading end of the recording paper P, which is bent and conveyed in the direction 4a, is brought into contact with the recording paper P to assist the separation of the recording paper P.

The spur 162, which is a spur member, has a plurality of projections 162a on its peripheral surface, and is provided rotatably about a rotation support shaft 165. The spur 162 guides the back side of the recording sheet P to convey the recording sheet P, prevents the back side toner image of the recording sheet P having the toner image on both sides from being disturbed, and transfers the recording sheet P to the fixing device 17. The recording paper P is stably conveyed to the fixing device 17 while keeping the entering direction constant.

The separation claw 210 and the spur 162 are positioned between the transfer material conveying surface of the intermediate transfer belt 14a or the extended surface thereof.
It is arranged on the opposite side of the photosensitive drum 10. It is also possible to provide spurs 162 as spur members on both sides of the transfer material conveying surface or an extension surface thereof.

A fixing device 17 serving as a fixing means includes a first fixing roller 17a having a heater therein and a second fixing roller 1a.
7b. The recording paper P is sandwiched by a nip portion T between the first fixing roller 17a and the second fixing roller 17b, and the recording is performed by applying heat and pressure. The toner image on the paper P is fixed.

Next, the image forming process will be described.

When the image forming body driving motor M2 (see FIG. 4) is started at the start of image recording, the photosensitive drum 10 is rotated clockwise as shown by the arrow in FIG. 1, and at the same time, the yellow (Y) scorotron charger 11 is turned on. The application of a potential to the photosensitive drum 10 is started by the charging action.

After a potential is applied to the photosensitive drum 10, the Y exposure optical system 12 starts image writing by a first color signal, that is, an electric signal corresponding to the Y image data. An electrostatic latent image corresponding to the Y image of the original image is formed on the front surface.

The latent image is reversely developed in a non-contact state by the Y developing device 13, so that a yellow (Y) toner image is formed on the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 from above the Y toner image by the charging action of the magenta (M) scorotron charger 11, and the second color signal, that is, the M color signal, is applied by the M exposure optical system 12. Image writing is performed by an electric signal corresponding to the image data, and the magenta (M) toner image is superimposed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. It is formed.

By the same process, the cyan (C) toner image corresponding to the third color signal is further superimposed by the cyan (C) scorotron charger 11, the exposure optical system 12 of C and the developing device 13 of C. The black (K) toner image corresponding to the fourth color signal is sequentially superimposed thereon by a black (K) scorotron charger 11, a K exposure optical system 12, and a K developing device 13. A superposed color toner image of four colors of yellow (Y), magenta (M), cyan (C) and black (K) is formed on the peripheral surface within one rotation of the photosensitive drum 10. (Toner image forming means).

These Y, M, C and K exposure optical systems 12
Image writing on the photosensitive layer of the photosensitive drum 10 is performed from the inside of the drum through the above-described translucent substrate. Therefore, the writing of the images corresponding to the second, third and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. Can be formed.

The superimposed color toner image, which is the back image formed on the photosensitive drum 10 as the image forming body by the above image forming process, is transferred to the transfer area 14b.
By the transfer device 14c as a first transfer unit, the transfer is performed collectively (first transfer) on the intermediate transfer belt 14a as the intermediate transfer body (FIG. 3A). At this time, uniform exposure may be performed by the simultaneous transfer exposure device 12d provided inside the photoconductor drum 10 so that good transfer is performed. The charge on the intermediate transfer belt 14a charged by the transfer device 14c is removed by the charge remover 14m.

After the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 16, the toner is transferred to a cleaning device 19 which is an image forming body cleaning means. The toner is cleaned by a cleaning blade 19a made of a rubber material in contact with the toner, and collected by a screw 19b in a toner discharge container (not shown). Further, the peripheral surface of the photosensitive drum 10
For example, a uniform exposure device 12 before charging using a light emitting diode
The history of the photosensitive drum 10 in the previous image formation is eliminated by the exposure by e.

After the superimposed color toner image serving as the back side image is formed on the intermediate transfer belt 14a as described above, the front side image is continuously formed on the photosensitive drum 10 in the same manner as the above color image forming process. Is formed (FIG. 3B). On this occasion,
The image data is changed so that the front surface image formed on the photoconductor drum 10 becomes a mirror image with respect to the rear surface image formed on the photoconductor drum 10.

With the formation of the surface image on the photosensitive drum 10, recording paper P as a transfer material is sent out from a paper feed cassette 15 as a transfer material storage means by a feed roller 15a, and is used as a transfer material feeding means. Timing roller 1
5b, driven by a timing roller drive motor M3 (see FIG. 4) and rotated by a timing roller 15b, the color toner image of the surface image formed on the photosensitive drum 10 and the intermediate transfer belt 14a. The image is fed to the transfer area 14b in synchronization with the color toner image of the back surface image carried. At this time, the fed recording paper P is charged to the same polarity as the toner by a paper charger 150 which is a transfer material charging means provided on the front side of the recording paper P,
The toner is attracted to the intermediate transfer belt 14a and fed to the transfer area 14b. By charging the paper with the same polarity as that of the toner, the toner is prevented from being attracted to the toner image on the intermediate transfer belt 14a and the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed.

In the transfer region 14b, a second voltage to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
The surface image on the photosensitive drum 10 is collectively transferred (second transfer) to the surface of the recording paper P by the transfer device 14c as the transfer means. At this time, the back surface image on the intermediate transfer belt 14a is not transferred to the recording paper P but exists on the intermediate transfer belt 14a. Transfer device 1 as second transfer means
At the time of the second transfer by 4c, uniform transfer is performed by a simultaneous transfer exposure unit 12d using a light emitting diode, for example, provided inside the photosensitive drum 10 in opposition to the transfer area 14b so that good transfer is performed. Exposure may be performed. The charge on the intermediate transfer belt 14a charged by the transfer device 14c is removed by the charge remover 14m.

The recording paper P on which the color toner image has been transferred to the front surface is conveyed to a back transfer device 14g as a third transfer means to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. Then, the back surface image on the peripheral surface of the intermediate transfer belt 14a is collectively transferred (third transfer) to the back surface of the recording paper P by the back transfer device 14g (FIG. 3).
(C)).

The recording paper P on which the color toner images are formed on both sides is formed by the curvature of the curvature portion KT of the intermediate transfer belt 14a and the paper as transfer material separating means provided at the end of the intermediate transfer belt 14a as necessary. The spur 162 provided on the transport unit 160 is separated from the intermediate transfer belt 14a by the static elimination action of the separation AC neutralizer 14h and the separation claw 210 provided on the transport unit 160 at a predetermined interval from the intermediate transfer belt 14a. Fixing device 17 as fixing means through
The toner image on the recording paper P is fixed by applying heat and pressure at a nip portion T between the first fixing roller 17a and the second fixing roller 17b. The recording paper P on which double-sided image recording has been performed is sent upside down and sent.
The sheet is discharged to a tray outside the apparatus by a discharge roller 18.

The toner remaining on the peripheral surface of the intermediate transfer belt 14a after the transfer is provided to face the guide roller 14f with the intermediate transfer belt 14a interposed therebetween, and is applied to the intermediate transfer belt 14a with the support shaft 142 as a rotation fulcrum. The intermediate transfer member is cleaned by an intermediate transfer member cleaning device 140 which is an intermediate transfer member cleaning unit having an intermediate transfer member cleaning blade 141 capable of contacting and releasing contact.

The toner remaining on the peripheral surface of the photoconductive drum 10 after the transfer is subjected to static elimination by the photoconductive drum AC static eliminator 16 and then cleaned by the cleaning device 19 to remove the toner. By 12e, the history of the photosensitive drum 10 in the previous image formation is eliminated, and the next image formation cycle is started.

By using the above-described method, since the superimposed color toner images are collectively transferred, color shift of the color image on the intermediate transfer belt 14a, scattering or rubbing of the toner, and the like are less likely to occur, and the image deterioration is less likely to occur. Double-sided color image formation is performed.

Although the color image forming apparatus has been described as an example of the image forming apparatus, the present invention is not necessarily limited to this, and a monochrome image forming process similar to that described with reference to FIG. It is also applied to the device. Further, in the image forming apparatus of the present invention, in addition to the double-sided image forming for forming an image on both sides of the transfer material as described in the image forming apparatus described above, an image is formed on only one side of the front side or the back side of the transfer material. Of course, single-sided image formation can also be performed.

The prevention of image step unevenness due to uneven drive of the image forming body by providing a speed difference between the linear speed of the image forming body and the linear speed of the intermediate transfer body will be described with reference to FIGS. FIG. 4 is an explanatory diagram showing a drive system for changing the image forming linear velocity, and FIG. 5 is a control block diagram of image forming timing.

According to FIG. 4 or FIG. 5, double-sided image formation and single-sided image formation only on the front surface or the back surface are performed by the image forming process as described above. The intermediate transfer belt 14a is
Although the contact pressure with the photosensitive drum 10 serves as a damper (brake) for attenuating the vibration which is generated when the photosensitive drum 10 rotates and becomes uneven in driving, the vibration is originally reduced.
When both are rotated at the same linear velocity, the tension (contact pressure) of the intermediate transfer belt 14a on the photosensitive drum 10 becomes weak,
The role of the damper was weakened, the drive unevenness of the photosensitive drum 10 was amplified, and the uneven drive of the amplified photosensitive drum 10 caused image step unevenness. In particular, at the time of surface image formation, since the recording paper P as a transfer material is interposed between the photosensitive drum 10 and the intermediate transfer belt 14a,
The contact pressure of the intermediate transfer belt 14a against the photosensitive drum 10 becomes weaker, and the role of the intermediate transfer belt 14a as a damper becomes weaker, so that slippage easily occurs between the two and the unevenness in driving of the photosensitive drum 10 The occurrence of unevenness in the image is remarkable. Therefore, when the surface toner image on the photosensitive drum 10 as the image forming body is transferred onto the recording paper P as the transfer material, the linear velocity of the photosensitive drum 10 as the image forming body and the intermediate transfer as the intermediate transfer body The linear velocity of the belt 14a is provided with a speed difference. For example, the linear velocity of the intermediate transfer belt 14a is set to be faster or slower than the linear velocity of the photosensitive drum 10, so that the photosensitive drum 10 is always regulated in one direction. The photosensitive drum 10 was rotated by applying a damper (brake) to the photosensitive drum 10 in the manner described above, and an experiment was conducted to prevent the occurrence of uneven image steps due to uneven driving of the photosensitive drum 10.

In the confirmation experiment, the linear velocity of the photosensitive drum 10 driven by the image forming body driving motor M2 was set to Vp (mm / s).
ec) The linear velocity of the intermediate transfer belt 14a driven by the intermediate transfer member drive motor M1 is set to Vb (mm / sec), and the relative speed between the photosensitive drum 10 and the intermediate transfer belt 14a at the time of forming the toner image on the surface is changed. The judgment was made based on the image quality (image quality) on the recording paper P when the speed difference (%) was changed. Table 1 shows the experimental results.

[0052]

[Table 1]

In Table 1, when the linear speed of the intermediate transfer belt 14a is made equal to the linear speed of the photosensitive drum 10, and when the relative speed difference (%) is 0, unevenness of the image due to drive unevenness occurs in the image. , The image quality is poor, and the intermediate transfer belt 1
When the linear speed of 4a is changed (increased or decreased) and the relative speed difference (%) is 0.01, unevenness in the image due to drive unevenness occurs slightly in the image, and the image quality is slightly poor. Met. Further, when the linear speed of the intermediate transfer belt 14a is changed (increased or decreased) and the relative speed difference (%) is 0.02 to 0.04, image unevenness due to drive unevenness does not occur. And the image quality was good and ○. When the relative speed difference (%) was 0.05, no unevenness of the image due to driving unevenness was observed, but the image was slightly rubbed by the slip and the image quality was good or slightly poor. Met. The result is that instead of increasing the linear speed of the intermediate transfer belt 14a, the photosensitive drum 1
0, or the intermediate transfer belt 14a
Similar results were obtained by increasing the linear velocity of the photosensitive drum 10 instead of decreasing the linear velocity of the photosensitive drum 10.

From the above results, the linear velocity of the photosensitive drum 10 as an image forming body is Vp (mm / sec), and the linear velocity of the intermediate transfer belt 14a as an intermediate transfer body is Vb (mm).
/ Sec), at least during formation of the toner image on the surface, the relative speed difference (%) between the photosensitive drum 10 and the intermediate transfer belt 14a is 0.015 ≦ | (Vb−Vp) / Vp | ≦ It was confirmed that the value of 0.05 prevents the occurrence of image step unevenness due to drive unevenness.

In the above description, for example, in backside image formation for transferring the backside toner image on the photosensitive drum 10 to the intermediate transfer belt 14a, the relative speed difference between the linear speed of the intermediate transfer belt 14a and the linear speed of the photosensitive drum 10 (%), (V
b-Vp) / Vp is set to 0, and in the surface image formation for transferring the surface toner image on the photosensitive drum 10 to the recording paper P, the linear velocity of the intermediate transfer belt 14a and the photosensitive drum 10
Relative velocity difference (%) from the linear velocity of (Vb−Vp) / Vp
When the linear transfer speed of the intermediate transfer belt 14a is increased to 0.03 to form an image, the surface image on the recording paper P expands. The image is written by changing the image timing by reducing the size. As a method of changing the image timing, the sending of the image data is changed to narrow the interval in the sub-scanning direction. In the case of the printer described above with reference to FIG. 1 as the image forming apparatus, the exposure optical system 12 described above with reference to FIG.
When an LED is used, the light emission timing in the sub-scanning direction is electrically changed. When a laser optical system is used, the rotational speed of the polygon mirror is increased, although it is technically somewhat difficult. In the case of a copying machine, the reading speed is changed. Further, with the change of the linear velocity of the intermediate transfer belt 14a, the timing of feeding the recording paper P to the intermediate transfer belt 14a by the timing roller 15b as the transfer material feeding means, and the timing of feeding the recording paper P It is also necessary to change the speed of the roller drive motor M3 to the same speed as the linear speed of the intermediate transfer belt 14a.

However, changing only one of the linear velocities is not preferable because the mechanism and the control are complicated, and it is not preferable. Therefore, in the case of the back side image forming for transferring the back side toner image on the photosensitive drum 10 to the intermediate transfer belt 14a. Also, in the surface image formation for transferring the surface toner image on the photosensitive drum 10 to the recording paper P, the relative speed difference (%) between the linear speed of the intermediate transfer belt 14a and the linear speed of the photosensitive drum 10,
Preferably, (Vb-Vp) / Vp is set to, for example, 0.03 to increase the linear speed of the intermediate transfer belt 14a to form an image. However, since the back side image (back side toner image) on the intermediate transfer belt 14a and the front side image on the recording paper P are stretched, the sub-scanning direction of the toner image on the photosensitive drum 10 is required in advance for both front and back image formation. The interval is reduced, and the image writing is performed by changing the image timing.
As a method of changing the image timing, the sending of the image data is changed to narrow the interval in the sub-scanning direction. As the image forming apparatus, in the case of the printer described above with reference to FIG. 1, when the LED described above with reference to FIG.
When electrically changing the light emission timing in the sub-scanning direction or using a laser optical system, it is technically somewhat difficult,
The number of rotations of the polygon mirror is increased. In the case of a copying machine, the reading speed is changed. Further, with the change in the linear velocity of the intermediate transfer belt 14a, the recording paper P of the timing roller 15b as a transfer material feeding unit is changed.
Changes in the timing of feeding to the intermediate transfer belt 14a,
It is also necessary to change the speed of the timing roller drive motor M3 for feeding the recording paper P to the same speed as the linear speed of the intermediate transfer belt 14a.

As shown in FIG. 5, in response to an external command from an external scanner, an external printer, or the like, a double-sided image forming program in the ROM or a single-sided image forming program on the front side or the back side is executed through the control unit. The Y, M, C, and K images are formed on the basis of the above. However, since there is a difference in the drive unevenness of the photosensitive drum 10, the intermediate transfer member drive motor M1 for driving the intermediate transfer belt 14a and the photosensitive drum The linear speed of the image forming body driving motor M2 for driving the image forming apparatus 10 is set to be variable, and the linear speed of either the photosensitive drum 10 or the intermediate transfer belt 14a is changed at the time of shipment of the image forming apparatus or at the time of maintenance by a serviceman, and the driving is performed. Adjust the speed so that there is no unevenness in the image due to unevenness.
At this time, as described above, it is necessary to change (expand or contract) the magnification in the sub-scanning direction of the front and back toner images on the photoconductor drum 10, but the photoconductor drum 10 or the intermediate transfer belt 14 a
The change speed is read by an encoder (not shown) provided in the printer. When the image forming apparatus is the printer described above with reference to FIG. 1, when the LED described above with reference to FIG. In the case where the light emission timing in the sub-scanning direction is automatically changed from the change speed through the control unit, or when a laser optical system is used, it is technically somewhat difficult. The number of rotations of the mirror is up or down.
In the case of a copying machine, the reading speed is automatically changed from the changed speed through the control unit. Further, with the change of the linear velocity of the intermediate transfer belt 14a, the timing of feeding the recording paper P to the intermediate transfer belt 14a by the timing roller 15b as the transfer material feeding means, and the timing of feeding the recording paper P The speed of the roller drive motor M3 is automatically changed to the same speed as the linear speed of the intermediate transfer belt 14a through the control unit.

In the above-described embodiment, when a latent image is formed on the photosensitive drum 10, the transfer device 14c as the first transfer means is set to the operating state (on state).
It is preferable that the intermediate transfer belt 14a is brought into close contact with the photosensitive drum 10, and the adhesion (pressing force) of the intermediate transfer belt 14a to the photosensitive drum 10 is increased to prevent drive unevenness.

As described above, it is possible to prevent the occurrence of unevenness in the image level caused by the unevenness in the driving of the image forming body.

[0060]

According to the present invention, it is possible to prevent unevenness in image steps caused by uneven driving of the image forming member when forming a double-sided image using the intermediate transfer member in contact with the image forming member.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a side sectional view of the image forming body of FIG. 1;

FIG. 3 is a diagram illustrating a toner image forming state in the image forming apparatus according to the present invention.

FIG. 4 is an explanatory diagram illustrating a drive system that changes an image forming linear velocity.

FIG. 5 is a control block diagram of image forming timing.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 exposure optical system 13 developing device 14 a intermediate transfer belt 14 c transfer device 14 g backside transfer device 14 h paper separation AC static eliminator 14 m static eliminator 17 fixing device M1 intermediate transfer body drive motor M2 image forming body drive motor M3 Timing roller drive motor P Recording paper

Continuation of the front page (72) Inventor Tetsu Haneda 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) 2H027 DA17 DA18 DA19 DA20 DC04 DE09 EC02 EC03 EC18 EC20 ED02 ED24 EE01 EE03 EE04 EE07 EE08 EF01 EF10 FA13 FD08 HB07 2H028 BA03 BA06 BA16 BB04 2H032 AA02 AA15 BA02 BA05 BA09 BA18 BA19 BA21 BA23 BA28 BA30 CA13 DA03 DA12 DA28

Claims (4)

[Claims] 1. An image forming body, a charging unit for charging the image forming body, an image writing unit for forming an image writing latent image on the charged image forming body, and a latent image formed on the image forming body Means for forming a toner image on the image forming body by developing means for developing a toner image on the image forming body; and transferring the toner image on the image forming body to the surface of the transferred toner image. And an endless belt-shaped intermediate transfer body that conveys a transfer material; a first transfer unit that transfers a toner image on the image forming body to the intermediate transfer body; and a transfer of the toner image on the image forming body. An image forming apparatus comprising: a second transfer unit configured to transfer a toner image on the intermediate transfer body to a back surface of the transfer material; and a linear velocity of the image formed body. Is Vp (mm / sec), the linear velocity of the intermediate transfer member Is defined as Vb (mm / sec). At least during formation of a toner image on the surface, the relative speed difference (%) between the image forming body and the intermediate transfer body is 0.015 ≦ | (Vb−Vp) /Vp|≦0.05. An image forming apparatus, wherein: 2. An image forming body, charging means for charging the image forming body, image writing means for forming an image writing latent image on the charged image forming body, and a latent image formed on the image forming body Means for forming a toner image on the image forming body by developing means for developing a toner image on the image forming body; and transferring the toner image on the image forming body to the surface of the transferred toner image. And an endless belt-shaped intermediate transfer body that conveys a transfer material; a first transfer unit that transfers a toner image on the image forming body to the intermediate transfer body; and a transfer of the toner image on the image forming body. An image forming apparatus comprising: a second transfer unit configured to transfer a toner image on the intermediate transfer body to a back surface of the transfer material; and a second transfer unit configured to transfer the toner image on the intermediate transfer body to a back surface of the transfer material. The linear velocity of the transfer body is variable, and the image forming body is Alternatively, the image forming apparatus performs expansion and contraction of a toner image formed on the image forming body according to a change in a linear velocity of the intermediate transfer body. 3. The image forming apparatus according to claim 2, wherein an image forming timing is changed in accordance with expansion and contraction of a toner image formed on the image forming body. 4. The image forming apparatus according to claim 1, further comprising:
4. The transfer means of claim 1, wherein
The image forming apparatus according to claim 1.