JPH11352801A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus with excellent image quality, which can eliminate positional deviation and has no color deviation. An image forming apparatus includes: a photoconductor 414 formed of a rotating body; and an intermediate transfer body 415 disposed to face the photoconductor and rotated in the same direction as the photoconductor in contact with the photoconductor. The surface speed of the intermediate transfer member 415 is set lower than the surface speed of the photosensitive member, and
5 One-way clutch 42 between the rotation driving means 457
The one-way clutch sets the rotation direction of the intermediate transfer body 415 to the idling direction.

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 using a photosensitive member and an intermediate transfer member, such as a color copying machine, and more particularly, to the occurrence of color misregistration when a plurality of colors are superposed. Not about technology.

[0002]

2. Description of the Related Art There is known a color image forming apparatus having a drum-shaped photosensitive member which is driven to rotate, and an intermediate transfer member which is arranged to face the photosensitive member and is rotated in the same direction as the photosensitive member. The photoconductor and the intermediate transfer member are partially in contact with each other, and the toner image on the photoconductor is transferred onto the intermediate transfer member. In the case of a color image, a color-separated toner image of each color is sequentially formed on the photoconductor, and the toner image of each color is transferred onto the intermediate transfer body one by one.

Further, a mark is provided on the intermediate transfer member, and the passage of the mark is detected by a mark detecting sensor provided at a fixed position, timing is measured, and an image forming process is started. By this image forming process, color-separated color images of each primary color are sequentially formed for each color on the photoconductor, and this toner image is transferred onto the intermediate transfer body.

In the case of a normal color image, two to four colors of the toner image are formed. Therefore, unless the toner images of the respective colors are accurately superimposed on the intermediate transfer member, a color shift occurs in the completed color image. Will happen.

Therefore, in such an image forming apparatus, the peripheral length ratio of the photosensitive member to the intermediate transfer member and the rotation means of the intermediate transfer member is made to be an integer, and further, the gears of each drive means and the timing belt are decelerated. With the ratio being an integer, the speed variation for each color is made equal to enable accurate alignment.

In the primary transfer portion, the photosensitive member and the intermediate transfer member are in close contact with each other to form a nip portion, and at the time of each charging, the contact force is increased by an electric force (Coulomb force). Even in such a state, if the circumferential length ratio between the photosensitive member and the intermediate transfer member is an integer, both of them rotate completely synchronously, and accurate toner image alignment can be performed.

[0007]

However, since the photoreceptor, the intermediate transfer member, and the means for driving the rotation of the intermediate transfer member are industrial products, there is always a certain dimensional variation. Due to this variation, the peripheral speeds of the photoreceptor and the intermediate transfer member are slightly different, and the difference is absorbed by a small slip in the primary transfer portion, and the alignment using the mark must always be performed under the same conditions. No.

However, as described above, in the primary transfer portion, frictional force is generated due to close contact due to Coulomb force, and the photosensitive member and the intermediate transfer member tend to rotate in synchronization. Furthermore, there is play in the rotational direction due to backlash of the drive system gears and timing belt, play between the pulley and the shaft, play of the photoconductor unit and the drive system, and the relative position between the mark detection and the drive means is shifted. And the reaction of the small peripheral speed difference causes the driven side of the photosensitive member or the intermediate transfer member to rotate faster than the driven side in the slower driving means.

Further, for example, if the driving means for the intermediate transfer member is eliminated and the intermediate transfer member can be rotated following the photosensitive member by the adhesion at the nip portion, accurate positioning can be performed. However, stable driving cannot be performed when a reaction force due to the inertial weight of the intermediate transfer member is generated, such as at the start of rotation, or in a state where little adhesion force is generated before the start of charging.

In view of these facts, it is an object of the present invention to provide an image forming apparatus which can eliminate the above-mentioned positional shift and has excellent image quality without color shift.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a photoreceptor comprising a rotating body and a photoreceptor which is disposed to face the photoreceptor and is in contact with the photoreceptor in the same direction. An intermediate transfer member to be rotated, wherein the surface speed of the intermediate transfer member is smaller than the surface speed of the photosensitive member, and a one-way clutch is provided between the intermediate transfer member and its rotation driving means. Wherein the one-way clutch sets the rotation direction of the intermediate transfer member to the idling direction.

[0012] Further, a structure in which a high friction coefficient portion is provided over the entire surface of the non-image forming area of the photoconductor and / or the intermediate transfer member, or the high friction coefficient portion is provided between the photoconductor and the intermediate transfer member. The transfer member may be configured to include a protrusion formed on one of the transfer members and a concave portion formed on the other.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an image forming apparatus of the present invention.

A color image reading apparatus (hereinafter referred to as a “color scanner”) 200 converts an image of a document 180 on a contact glass 202 into an illumination lamp 205 and a mirror group 204.
A, 204B, 204C, etc., and an image formed on the color sensor 207 via the lens 206, and color image information of the original is converted into, for example, blue (hereinafter, referred to as "B"), green (hereinafter, referred to as "G"), Red (hereinafter referred to as "R")
Is read for each color separation light and is converted into an electric image signal.

In this example, the color sensor 207 is B,
It is composed of G and R color separation means and a photoelectric conversion element such as a CCD (solid-state imaging device), and performs simultaneous reading of three colors.

Based on the B, G, and R color separation image signal intensity levels obtained by the color scanner 200, a color conversion process is performed by an image processing unit (not shown) to obtain black (hereinafter referred to as "BK"). , Cyan (hereinafter referred to as “C”), magenta (hereinafter referred to as “M”), and yellow (hereinafter referred to as “Y”).

Using the color image data, a color image recording apparatus (hereinafter referred to as "color printer") described below is used.
The operation system of the color scanner 200 for obtaining the BK, C, M, and Y image data according to the operation of the color printer 400 receives a scanner start signal at the same time as the operation of the color printer 400. The illumination / mirror optical system including the mirror groups 204A, 204B, 204C and the like scans the original in the direction of the arrow, and obtains one color image data for each scan. Each time, the color printer 400 sequentially superimposes these while visualizing the image to form a four-color image.

Next, an outline of the color printer 400 will be described. Writing optical unit 401 as exposure means
Converts the color image data from the color scanner 200 into an optical signal, performs optical writing corresponding to the original image, and applies an electrostatic charge to the photosensitive drum 414 which is a latent image carrier corresponding to the photosensitive member according to the present invention. Form a latent image.

The optical writing unit 401 includes a laser light emitting unit 441, a light emission drive control unit (not shown) for driving the same, a polygon mirror 443, a rotation motor 444 for driving the same, a fθ lens 442, a reflection mirror 446, etc. It is composed of

The photosensitive drum 414 rotates counterclockwise, as indicated by the arrow. Around the photosensitive drum cleaning unit 421, a neutralization lamp 414M, a charger 419 as a charging unit, and a photosensitive drum 414 are provided. Potential sensor 414D for detecting latent image potential, revolver developing device 42
0 selected developing device, developing density pattern detector 414
P, an intermediate transfer belt 4 as an intermediate transfer member according to the present invention
15, etc. are arranged.

The revolver developing device 420 includes a BK developing device 420K, a C developing device 420C, an M developing device 420M, and a Y developing device 420Y, and a revolver rotating section (R) that rotates each developing device in a counterclockwise direction as indicated by an arrow. (Not shown). In order to develop the electrostatic latent image, each of these developing units is provided with a developing sleeve 420KS, 420CS, 420M that rotates by bringing a developer into contact with the surface of the photosensitive drum 414.
S, 420YS and a rotating developing paddle for pumping up and stirring the developer.

In the standby state, the revolver developing device 420 is set at a position where development is performed by the BK developing device 420. When the copying operation is started, the BK image data is read from the color scanner 200 at a predetermined timing. Starts, and based on this image data, optical writing and latent image formation by laser light begin (hereinafter, an electrostatic image based on BK image data is referred to as “BK latent image”, C, M, Y).
The same for each image data).

In order to enable development from the leading end of the BK latent image, the developing sleeve 420KS is started to rotate before the leading end of the latent image reaches the developing position of the BK developing unit 420K.
The K latent image is developed with BK toner.

Thereafter, the developing operation of the BK latent image area is continued. When the rear end of the latent image passes the BK latent image position, the developing operation of the next color is immediately performed from the developing position by the BK developing device 420K. The revolver developing device 420 is driven and rotated to the developing position by the container. This rotation operation is completed at least before the leading end of the latent image based on the next image data arrives.

When the image forming cycle is started, the photosensitive drum 414 rotates counterclockwise as indicated by an arrow, and the intermediate transfer belt 415 rotates clockwise by a drive motor (not shown). I do.

As the intermediate transfer belt 415 rotates, B
K toner image formation, C toner image formation, M toner image formation, Y
Toner image formation is sequentially performed, and finally BK, C, M, Y
And a toner image is formed on the intermediate transfer belt 415 in this order.

The formation of the BK image is performed as follows. The charger 419 uniformly charges the photosensitive drum 414 with a negative charge to about -700 V in the dark by corona discharge. Subsequently, the laser diode 441 performs raster exposure based on the BK signal. When the raster image is thus exposed, the photosensitive drum 4 that is initially uniformly charged
In the exposed portion 14, the charge proportional to the amount of exposure light disappears, and an electrostatic latent image is formed.

The toner in the revolver developing device 420 is
It is negatively charged by stirring with the ferrite carrier, and the BK developing sleeve 420KS of the present developing device.
Is biased by a power supply (not shown) with respect to the metal base layer of the photosensitive drum 414 to a potential at which a negative DC potential and an AC are superimposed.

As a result, no toner adheres to the portion of the photosensitive drum 414 where the charge remains, and the BK toner is attracted to the portion having no charge, that is, the exposed portion, and the same BK toner as the latent image. A visible image is formed.

The intermediate transfer belt 415 is connected to the driving roller 41
5D, a transfer opposing roller 415T, a cleaning opposing roller 415C, and a group of driven rollers, which are driven and controlled by a drive motor (not shown).

The BK toner image formed on the photosensitive drum 414 is placed on the surface of the intermediate transfer belt 415, which is moving at a constant speed in contact with the photosensitive drum, by a belt transfer corona discharger (hereinafter referred to as a "belt transfer portion"). ) 416. Hereinafter, the photosensitive drum 414 to the intermediate transfer belt 4
Transfer of the toner image to the toner image 15 is referred to as belt transfer.

Some untransferred residual toner on the photoconductor drum 414 is cleaned by the photoconductor cleaning unit 421 in preparation for reuse of the photoconductor drum 414. The collected toner is stored in a waste toner tank (not shown) via a collection pipe.

The intermediate transfer belt 415 sequentially aligns the BK, C, M, and Y toner images formed on the photosensitive drum 414 on the same surface to form a four-color superimposed belt transfer image. Then, collective transfer is performed on transfer paper by a corona discharge transfer device.

On the photosensitive drum 414 side, B
After the K image forming process, the process proceeds to the C image forming process.
From a predetermined timing, C by the color scanner 200
Reading of image data starts, and a latent image of C is formed by laser light writing based on the image data.

The C developing device 420C rotates the revolver developing device with respect to the developing position after the trailing edge of the preceding BK latent image has passed and before the leading end of the C latent image has arrived. , C latent image is developed with C toner.

Thereafter, the development of the C latent image area is continued, but when the rear end of the latent image has passed, the revolver developing device 420 is driven in the same manner as in the case of the BK developing device, and the C developing device 42
0C is sent out, and the next M developing device 420M is positioned at the developing position. This operation is also performed before the leading end of the next M latent image reaches the developing unit.

The steps for forming the M and Y images are the same as those for the BK image and C image, since the operations of reading, latent image formation and development of the respective image data are the same as those described above. .

The belt cleaning device 415U includes an inlet seal, a rubber blade, a discharge coil, and a mechanism for contacting and separating the inlet seal and the rubber blade. 1
While the second, third, and fourth color images are being belt-transferred after the color-transferred BK image is belt-transferred, the entrance seal, the rubber blade, and the like are separated from the intermediate transfer body surface by the blade contact / separation mechanism.

A paper transfer corona discharger (hereinafter, referred to as a “paper transfer device”) 417 uses an AC corona discharge method to transfer the superposed toner image on the intermediate transfer belt 415 to transfer paper.
+ DC or a DC component is applied to the transfer paper and the intermediate transfer member.

The transfer paper cassette 482 in the paper supply bank stores transfer papers of various sizes. The registration roller pair 418R is supplied from the storage cassette storing paper of the designated size by the paper supply roller 483. The paper is fed and transported in the direction. Reference numeral 412B2 indicates a paper feed tray for manually feeding OHP paper, thick paper, and the like.

At the time when the image formation is started, the transfer paper is fed from any one of the above-mentioned paper feed trays, and stands by at the nip portion of the registration roller pair 418R. When the leading end of the toner image on the intermediate transfer belt 415 approaches the paper transfer unit 417, the registration roller pair 418R is driven so that the leading end of the transfer paper coincides with the leading end of this image, and the registration of the paper and the image is performed. Matching is performed.

In this way, the transfer paper 41 is superposed on the color superimposed image on the intermediate transfer body and connected to the positive potential.
Pass over 7 At this time, the transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when the transfer paper passes through a separation static eliminator by a static elimination brush (not shown) disposed on the left side of the paper transfer device 417, the transfer paper is discharged, separated from the intermediate transfer belt 415, and moved to the paper transport belt 422.

The transfer paper on which the four-color superimposed toner image has been collectively transferred from the surface of the intermediate transfer member is fixed to a fixing device 42 by a paper transport belt 422.
The toner image is melted and fixed at a nip portion between a fixing roller 423A and a pressure roller 423B controlled to a predetermined temperature, sent out of the main body by a discharge roll pair 424, and stacked face up on a copy tray (not shown). , Get a full color copy.

The photosensitive drum 414 after belt transfer
Has its surface cleaned by a photoconductor cleaning unit 421 including a brush roller, a rubber blade, and the like.
Further, the charge is uniformly removed by the charge removing lamp 414M.

After the transfer of the toner image to the transfer paper, the intermediate transfer belt 415 is again
The surface is cleaned by pressing the blade with a 15U blade contact / separation mechanism.

In the case of the repeat copy, the operation of the color scanner and the image formation on the photosensitive member proceed to the second color first color image process at a predetermined timing after the first color image process.

Further, the intermediate transfer belt 415 follows the batch transfer process of the first four-color superimposed image onto the transfer paper, and the surface of the intermediate transfer belt 415 is cleaned by the belt cleaning device. The image is transferred to the belt. Thereafter, the operation is the same as that of the first sheet.

The above is the description of the copy mode for obtaining the four-color full-color copy. However, in the case of the three-color copy mode and the two-color copy mode, the number of specified colors and the number of times are limited.
The same operation as described above will be performed.

In the case of the single-color copy mode, the revolver developing device 420 is operated until the predetermined number of dances is completed.
Only the developing device of the predetermined color is positioned at the developing position to be in the developing operation state, and the copying operation is continuously performed while the blade of the belt cleaning device 415U is pressed against the belt.

In such an image forming apparatus, a mark for position detection is provided on the outer peripheral surface or the inner peripheral surface of the intermediate transfer belt 415. However, as for the outer peripheral surface, it is necessary to devise a way to avoid the passage area of the belt cleaning device 415U, which may cause difficulty in arrangement. In this case, the outer peripheral surface is provided on the inner peripheral surface side. Although not shown in FIG. 1, the optical sensor is provided at a position between a driving roller 415D that supports the belt 415 and a support roller 415F.

FIGS. 2 and 3 are views for explaining the detailed arrangement of the photosensitive member and the intermediate transfer member of the image forming apparatus. A timing pulley 451 is connected to the photosensitive drum 414, and a timing pulley 452 is connected via a one-way clutch 426 to a driving roller 415 </ b> D of the intermediate transfer belt 415 disposed to face. This one-way clutch 4
Reference numeral 26 is installed such that the idling direction is the rotation direction of the intermediate transfer belt 415 (the direction of arrow a in FIG. 3). A timing belt 454 is wound between the timing pulleys 451 and 452, and two tension pulleys 456 are provided in the middle to adjust the tension of the timing belt 454.

A timing gear 458 is mounted coaxially with the timing pulley 452, and a driving gear 457A of a driving motor 457 meshes with the timing gear 458. The circumferential length ratio between the photosensitive drum 414 and the intermediate transfer body is such that the circumferential length of the photosensitive body: the circumferential length of the intermediate transfer body = 1: 2. Further, the relationship between the number of teeth T1 of the timing pulley 451 and the number of teeth T2 of 452 is T1> T2 × 2, and the surface speed of the intermediate transfer belt 415 is lower than the surface speed of the photoconductor. Have been.

When the copying operation is started and the apparatus starts operating, the photosensitive drum 414 starts rotating, and at the same time, the drive motor 457 starts rotating. The rotation of the drive motor 457 is transmitted from the drive gear 457A to the timing gear 458, and the shaft of the drive roller 415D rotates in the direction of arrow b in FIG. When the timing gear rotates in this direction, the one-way clutch 426 is locked, so that the intermediate transfer belt 415 also starts rotating against its own inertia.

As described above, the timing pulley 451
And 452, the speed at which the intermediate transfer belt 415 is driven is reduced even if the photosensitive drum 414 reaches the rated rotation speed. However, the photosensitive drum 414 and the intermediate transfer belt 415 are in contact with each other at the transfer section, and the intermediate transfer belt 415 is pulled at a high speed of the photosensitive drum 414. And this direction is the one-way clutch 4
26, the intermediate transfer belt 415 is rotated at the same surface speed as the photosensitive drum 414 by the frictional force with the photosensitive drum 414 and the Coulomb force due to charging.

FIG. 4 shows another embodiment of the present invention, in which the photosensitive drum 414 and the end of the intermediate transfer belt 415 are coated with rubber as high friction coefficient portions 470 and 471 over the entire circumference. It is. This high friction coefficient part 47
0,471 are the photosensitive drum 414 and the intermediate transfer drum 4
Either one of 15 may be used. Further, it is desirable to form the non-image area avoiding the image area.

FIG. 5 shows still another embodiment of the present invention, in which a large number of hemispherical projections 480 are formed on the photosensitive drum 414 as a high friction coefficient part over the entire periphery of the photosensitive drum 414 to form an intermediate transfer member. Has a recess 481 into which these projections are fitted. The recess 481 is formed as a hole in this embodiment.

[0057]

As described above, according to the present invention, a photoreceptor composed of a rotating body, and a photoreceptor arranged opposite to the photoreceptor and rotated in the same direction as the photoreceptor in contact with the photoreceptor. And an intermediate transfer member, the image forming apparatus having a surface speed of the intermediate transfer member less than the surface speed of the photoreceptor,
In addition, since a one-way clutch is provided between the intermediate transfer member and its rotation driving means, and the one-way clutch sets the rotation direction of the intermediate transfer member to the idling direction, the surface speed between the photosensitive member and the intermediate transfer member is reduced. As a result, even when a plurality of colors are superimposed and formed like a full-color image, it is possible to obtain a good image with no displacement.

If a high friction coefficient portion is provided on the entire surface of the non-image forming area of the photoreceptor and / or the intermediate transfer member, the frictional force due to the close contact increases, and more stable synchronization is achieved. You can get a spin.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus of the present invention.

FIG. 2 is a diagram illustrating a detailed configuration of a main part of the image forming apparatus of FIG. 1;

FIG. 3 is a perspective view showing a drive structure of a photoconductor and an intermediate transfer member.

FIG. 4 is a diagram illustrating a state in which a high friction coefficient portion is provided at an end of a photoconductor and an intermediate transfer member.

FIG. 5 is a view showing a state in which a projection and a concave portion are provided as a high friction coefficient portion.

[Description of Signs] 414 Photoconductor 415 Intermediate Transfer Body 426 One-way Clutch 457 Rotation Drive Means 470,471 High Friction Coefficient Section 480 Projection 481 Depression

Claims (3)

[Claims] 1. An image forming apparatus comprising: a photoreceptor formed of a rotating body; and an intermediate transfer body disposed to face the photoreceptor and rotated in the same direction as the photoreceptor in contact with the photoreceptor. The surface speed of the intermediate transfer member is made lower than the surface speed of the photoreceptor, and a one-way clutch is provided between the intermediate transfer member and its rotation driving means. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein a high friction coefficient portion is provided over the entire surface of the non-image forming area of the photoconductor and / or the intermediate transfer body. 3. The high friction coefficient portion comprises a projection formed on one of the photoreceptor and the intermediate transfer member and a recess formed on the other. Image forming apparatus.