JP2023028836A - Image forming apparatus and method for controlling the same - Google Patents

Abstract

To provide an image forming apparatus and the like that can eliminate bending of an intermediate transfer belt when performing image formation to prevent color shift with a simple configuration.SOLUTION: An image forming unit of an image forming apparatus comprises: a developing unit that develops a plurality of photoreceptor drums to form toner images in colors different from each other; a driving system that drives the plurality of photoreceptor drums independently of each other; an intermediate transfer belt that is in contact with the plurality of photoreceptor drums and to which the toner images in the respective colors are transferred; a mechanism that brings the intermediate transfer belt into contact with the photoreceptor drums during toner image transfer, and separates the intermediate transfer belt from the photoreceptor drums in a period other than the image transfer; and a secondary transfer unit that transfers the toner images on the intermediate transfer belt to a sheet. During a period from when the intermediate transfer belt is brought into contact with the photoreceptor drums until when image forming processing is started, a control unit adjusts the rotation speed of the photoreceptor drums to a speed different from a steady rotation speed.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to an image forming apparatus and the like.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a color multifunction machine, developed images of respective colors formed on different image carriers (photosensitive drums) are superimposed on an intermediate transfer belt for intermediate transfer, and transferred to a recording paper. In this type of image forming apparatus, the degree of alignment is important when the developer images are superimposed and transferred.

Japanese Unexamined Patent Application Publication No. 2002-100000 discloses a mechanism in which an encoder sensor is provided on an intermediate transfer belt/photosensitive drum, and speed control is performed based on the measurement results of the encoder sensor.

However, the speed difference controlled by this configuration is due to roller eccentricity and the like, and is actually on the order of 0.1% or more. Therefore, it is necessary to mount an encoder with a high level of resolution and reading accuracy used in research and development on the disposable intermediate transfer belt and photosensitive drum, which is not realistic. In addition, since the belt has elasticity and changes depending on the life and temperature, it is not possible to accurately measure the speed with the method of providing slits on the belt as in the example of Patent Document 1, and the transfer cleaning blade is caught. Such adverse effects occur.

Further, Japanese Patent Application Laid-Open No. 2002-100001 discloses detecting a change in the speed of the drum and the belt based on the difference in the deviation amount of the toner patch on the belt between when the developing roller is in contact with the photosensitive drum and when it is separated from the photosensitive drum. Mechanisms for compensating for misalignment are disclosed.

JP 2011-81270 A JP 2013-80247 A

However, in order to extend the life of the intermediate transfer belt (life until replacement time), the tension of the intermediate transfer belt may be lowered during printing standby. , the intermediate transfer belt between the photoreceptor drums remains flexed, and the speed of the intermediate transfer belt gradually changes as the flexion disappears.

Since this minute change in belt speed appears in printing as a color shift in the transport direction, there is a problem that color shift in the transport direction occurs on the first to several pages of printing of a plurality of sheets.

Patent document 1 and patent document 2 are complicated because a dedicated sensor is installed. Moreover, since it is not related to the timing at which the photosensitive drum contacts and separates from the intermediate transfer belt, it is not possible to suppress the belt velocity change factor.

In view of such circumstances, the present disclosure provides an image forming apparatus and the like that can prevent color misregistration by eliminating bending of an intermediate transfer belt when forming an image with a simple configuration.

The present disclosure includes an image forming unit that forms an image on a predetermined sheet of paper using an electrophotographic method, and a control unit that controls the image forming unit, and the image forming unit develops a plurality of photosensitive drums. a developing device for forming toner images of different colors on each surface; a drive system for independently driving the plurality of photoreceptor drums; a belt, a mechanism for bringing the intermediate transfer belt into contact with the photosensitive drum during toner image transfer and separating the intermediate transfer belt from the photosensitive drum except during image transfer; a transfer unit, wherein the control unit keeps the rotation speed of the photoreceptor drum different from the normal rotation speed after the intermediate transfer belt is brought into contact with the photoreceptor drum until the image forming process is started. The image forming apparatus is characterized in that the speed is set.

The present disclosure includes a step of independently driving a plurality of photoreceptor drums, and a process of bringing the intermediate transfer belt into contact with the photoreceptor drums when transferring an image onto the intermediate transfer belt, and driving the photoreceptor drums away from the photoreceptor drums except during image transfer. a secondary transfer step of transferring the toner image on the intermediate transfer drum onto a sheet; and a control step of controlling the driving system of the image forming unit, wherein the control step includes moving the intermediate transfer belt. In the control method of the image forming apparatus, the rotation speed of the photoreceptor drum is set to a speed different from the normal rotation speed from the time when the photoreceptor drum is brought into contact with the photoreceptor drum until the image forming process is started.

According to the image forming apparatus and the like of the present disclosure, an excellent effect can be obtained in that it is possible to prevent color misregistration by eliminating bending of the intermediate transfer belt when forming an image with a simple configuration.

1 is an overall view of an image forming apparatus according to an embodiment; FIG. 3 is a control block diagram of the image forming apparatus; FIG. FIG. 3 is an explanatory diagram of an intermediate transfer belt unit; 4A and 4B are explanatory diagrams of the behavior of the intermediate transfer belt when the control of the first embodiment is performed; FIG. It is the same explanatory view. FIG. 10 is an explanatory diagram of the behavior of the intermediate transfer belt when the control of the second embodiment is performed; It is the same explanatory view. FIG. 10 is an explanatory diagram of color misregistration in the sub-scanning direction due to changes in belt speed; FIG. 10 is an explanatory diagram of color misregistration data in the sub-scanning direction; FIG. 10 is an explanatory diagram of control of the image forming apparatus according to the second embodiment; It is explanatory drawing of the effect of 2nd Embodiment. FIG. 11 is a comparative explanatory diagram of color misregistration in the second embodiment; FIG. 11 is an explanatory diagram of control of the image forming apparatus according to the third embodiment; It is the same explanatory view. It is the same explanatory view. FIG. 11 is an explanatory diagram of control of an image forming apparatus according to a fourth embodiment;

Hereinafter, embodiments will be described with reference to the accompanying drawings.
[1. First Embodiment]

FIG. 1 is an example of an image forming apparatus according to the first embodiment, and is an explanatory diagram showing the configuration of an image forming apparatus having an intermediate transfer belt.
[1.1 Overall configuration]

As shown in FIG. 1, the image forming apparatus 100 according to the embodiment forms multicolor and monochromatic images on a predetermined sheet (paper) by electrophotography according to image data transmitted from the outside. 1, and relates to an image forming apparatus having an intermediate transfer belt 61 on which a toner image is temporarily carried.

As shown in FIG. 1, the image forming apparatus 100 forms multicolor and monochromatic images on a predetermined sheet (for example, recording sheet) according to image data transmitted from the outside. image forming unit 110 and an automatic document processor 120 .
[1.2 Functional configuration]

1 and 2, the image forming section 110 mainly includes an exposure unit 1, a developing device 2, a photosensitive drum 3, a cleaner unit 4, a charger 5, an intermediate transfer belt unit 6, a fixing unit 7, It is configured to have a paper feed cassette 81, a paper discharge tray 91, and the like.

Schematically, as shown in FIG. 2, the image forming apparatus 100 has an image forming section 110 that electrophotographically forms an image on a predetermined sheet, and a control section 20 that controls the image forming section 110 .

The image forming unit 110 includes a plurality of photoreceptor drums 3 (four photoreceptor drums (3Y, 3M, 3C, 3BK) to be described later) on which electrostatic latent images are formed, and a plurality of photoreceptor drums 3 (3Y, 3M). , 3C, and 3BK) with toner to form toner images of different colors (Y, M, C, and BK to be described later), and a plurality of photosensitive drums 3, which are driven independently. an intermediate transfer belt 61 on which toner images of respective colors are transferred in contact with a plurality of photosensitive drums 3; It includes a mechanism for separating from the body drum 3 and a transfer roller 10 of a secondary transfer portion for transferring the toner image on the intermediate transfer belt 61 to paper.

The controller 20 sets the rotation speed of the photoreceptor drum 3 to a speed different from the normal rotation speed after the intermediate transfer belt 61 is brought into contact with the photoreceptor drum until the image forming process is started.

Specifically, above the image reading unit 90 provided on the upper part of the image forming unit 110, a document table 92 made of transparent glass on which a document is placed is provided. An automatic document processor 120 is attached.

The automatic document processor 120 is configured to automatically convey the document onto the document table 92 . The automatic document processing apparatus 120 is configured to be rotatable in the direction of arrow M, and the document can be manually placed by opening the document table 92 .

The image data handled by the image forming apparatus 100 corresponds to a color image using each color of yellow (Y), magenta (M), cyan (C), and black (BK).

Accordingly, the image forming section 110 is provided with four developing devices 2, photosensitive drums 3, charging devices 5, and cleaner units 4, four of which are provided so as to form four types of latent images corresponding to the respective colors. (Y), magenta (M), cyan (C), and black (BK).

With these components, the image forming section 110 has four image stations along the feeding direction of the intermediate transfer belt 61 , each of which includes the developing device 2 , the photosensitive drum 3 , the charging device 5 , and the cleaner unit 4 .

The photosensitive drums 3 of respective colors are arranged in order of 3Y, 3M, 3C, and 3BK from the upstream side (intermediate transfer belt driven roller 63 side) of the intermediate transfer belt 61 to the downstream side (intermediate transfer belt drive roller 62). are placed.

In addition to the four colors of yellow (Y), magenta (M), cyan (C), and black (BK), for example, cyan (C) and magenta (M) have the same hue and lower density. Six colors including light cyan (LC) and light magenta (LM) may be used. A plurality of combinations including other colors may be used as long as they are a plurality of colors.

By using these six colors, it is possible to obtain a clearer, high-quality full-color image.

The charger 5 is charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. Instead of the charger-type charger 5, a contact-type roller-type or brush-type charger may be used.

The exposure unit 1 exposes a charged photosensitive drum 3 according to image data input from the outside or image data obtained by reading a document, thereby forming an electrostatic latent image corresponding to the image data onto the photosensitive drum. It is an image writing device for forming images on the surface of the drum 3, and is configured as a laser scanning unit (LSU) having a laser emitting section, a reflecting mirror, and the like.

The exposure unit 1 includes a polygon mirror for scanning a laser beam and optical elements such as lenses and mirrors for guiding the laser beam reflected by the polygon mirror to the photosensitive drum 3 . In addition, as the exposure unit 1, a method using an EL or an LED writing head in which light emitting elements are arranged in an array can also be adopted.

The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 (3Y, 3M, 3C, 3BK) with toner of four colors (Y, M, C, BK). is.

Each photoreceptor drum 3 (3Y, 3M, 3C, 3BK) has a cylindrical shape and is disposed above the exposure unit 1. Its surface is cleaned by the cleaner unit 4, and the cleaned surface is cleaned by the charger 5. Uniformly charged.

The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer. The cleaner unit 4 is provided with a cleaning blade 41 and a waste toner conveying screw 42 .

The intermediate transfer belt unit 6 is arranged above the photosensitive drums 3 and includes an intermediate transfer belt 61, an intermediate transfer belt driving roller 62, an intermediate transfer belt driven roller 63, an intermediate transfer roller 64, and an intermediate transfer belt cleaning device (cleaning device). ) 65.

The intermediate transfer belt drive roller 62, the intermediate transfer belt driven roller 63, and the intermediate transfer roller 64 are configured to stretch the intermediate transfer belt 61 and rotate it.

The intermediate transfer roller 64 provides a transfer bias for transferring the toner images of the four photosensitive drums 3 (3Y, 3M, 3C, 3BK) onto the intermediate transfer belt 61. , and BK.

The intermediate transfer roller 64 is, for example, a sponge-like roller installed at a position to be paired with each photoreceptor drum 3, and is pressed so as to come close to the photoreceptor drum 3 at the timing of transfer.

In other words, although the toner on the photosensitive drum 3 is pressed against the intermediate transfer belt 61, in order to cope with the phenomenon that the toner cannot be completely moved by this alone, transfer is performed by applying a charge opposite to that on the surface of the photosensitive drum 3. It is configured to generate bias static electricity and attract toner. A pressure mechanism and a transfer bias circuit are omitted from the drawing.

The intermediate transfer belt 61 is formed endlessly using a film having a thickness of about 100 μm to 150 μm, and is provided so as to come into contact with each photosensitive drum 3 . The intermediate transfer belt 61 sequentially superimposes and transfers the respective color toner images (Y, M, C, BK) formed on the photosensitive drums 3 onto the intermediate transfer belt 61, thereby forming a color toner image. It has the function of forming a (multicolor toner image).

The transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 61 is performed by the intermediate transfer roller 64 which is in contact with the back side of the intermediate transfer belt 61 . A high-voltage transfer bias (a high voltage having a polarity (+) opposite to the charge polarity (-) of the toner) is applied to the intermediate transfer roller 64 to transfer the toner image.

The intermediate transfer roller 64 is based on a shaft made of metal (eg, stainless steel) with a diameter of 8 to 10 mm, and the surface of the shaft is covered with a conductive elastic material (eg, EPDM, urethane foam, etc.). It is A high voltage is uniformly applied to the intermediate transfer belt 61 by this conductive elastic material.

Although the roller-shaped intermediate transfer roller 64 is used as the transfer electrode in the embodiment, it is also possible to use a brush-shaped electrode or the like.

As described above, the toner images visualized on each photosensitive drum 3 according to each hue are laminated on the intermediate transfer belt 61 . As the intermediate transfer belt 61 rotates, the image information on which the toner image is laminated in this way is transferred onto the paper by the transfer roller 10 arranged at the contact position between the paper and the intermediate transfer belt 61 .

At this time, the intermediate transfer belt 61 and the transfer roller 10 are pressed against each other at a predetermined nip, and the voltage applied to the transfer roller 10 for transferring the toner onto the paper, that is, the opposite polarity (-) of the toner charge polarity (-) is applied to the transfer roller 10. +) is applied.

Furthermore, in order for the transfer roller 10 to constantly obtain a predetermined nip, one of the transfer roller 10 and the intermediate transfer belt drive roller 62 is made of a hard material (such as metal), and the other is made of a soft material such as an elastic roller (elastic rubber roller). , or a foamed resin roller) is used.

Further, as described above, the toner adhering to the intermediate transfer belt 61 due to contact with the photosensitive drum 3 or the toner remaining on the intermediate transfer belt 61 without being transferred onto the paper by the transfer roller 10 is transferred to the next process. Since it causes color mixture of toner in the toner image formed in , it is configured to be removed and collected by the intermediate transfer belt cleaning device 65 .

The intermediate transfer belt cleaning device 65 includes, for example, a cleaning blade 651 that is in contact with the intermediate transfer belt 61 and serves as a cleaning member for removing toner remaining on the intermediate transfer belt 61 , and residual toner (waste toner) collected by the cleaning blade 651 . A waste toner conveying screw 652 is provided for conveying toner) to a collection container (not shown).

The intermediate transfer belt 61 with which the cleaning blade 651 contacts is supported by the intermediate transfer belt driven roller 63 from the rear side.

The paper feed cassette 81 is a tray for storing paper used for image formation, and is provided below the exposure unit 1 of the image forming section 110 . Paper used for image formation can also be placed in a manual paper feed cassette 82 provided on the outer side of the image forming section 110 .

The paper discharge tray 91 is provided above the image forming section 110 and is a tray for stacking printed paper face down.

The image forming unit 110 also includes a substantially vertical paper transport path S for transporting paper from the paper feed cassette 81 and the manual paper feed cassette 82 to the paper discharge tray 91 via the transfer roller 10 and the fixing unit 7 . is provided.

Pickup rollers 11a and 11b, a plurality of conveying rollers 12a to 12d, a registration roller 13, a transfer roller 10, and a fixing unit are provided in the vicinity of the paper transport path S from the paper feed cassette 81 to the manual paper feed cassette 82 to the paper discharge tray 91. 7 is provided.

The transport rollers 12a to 12d are small rollers for promoting and assisting transport of the paper, and are provided along the paper transport path S in plurality. The conveying roller 12b functions as a paper discharge roller for discharging the paper to the paper discharge tray 91, and is therefore referred to as a paper discharge roller.

The pickup roller 11 a is provided near the end of the paper feed cassette 81 , picks up the paper sheets one by one from the paper feed cassette 81 , and supplies the paper to the paper transport path S.

The pickup roller 11 b is provided near the end of the manual paper feed cassette 82 , picks up the sheets one by one from the manual paper feed cassette 82 , and supplies them to the paper transport path S.

The registration rollers 13 have the function of temporarily holding the sheet being conveyed on the sheet conveying path S and conveying the sheet to the transfer roller 10 at the timing when the leading edge of the toner image on the photosensitive drum 3 and the leading edge of the sheet are aligned. are doing.

The fixing unit 7 has a heat roller 71 and a pressure roller 72 .
The heat roller 71 and the pressure roller 72 rotate and convey the paper while sandwiching it.
The heat roller 71 is set to a predetermined fixing temperature by the controller based on a signal from a temperature detector (not shown). It has a function of melting, mixing, and press-contacting the multi-color toner image transferred to the paper by thermally pressing the toner onto the paper together with the pressure roller 72, and thermally fixing it to the paper.

The fixing unit 7 is also provided with an external heating belt 73 for heating the heat roller 71 from the outside.

Like the heat roller 71, the pressure roller 72 is configured by providing an elastic layer on the peripheral surface of a cylindrical metal core. Then, it abuts against the heat roller 71 with a predetermined pressure.

[1.3 System configuration]
An outline of the system configuration of the image forming apparatus 100 will be described with reference to FIG.

As shown in FIG. 2, the control unit 20 is a functional unit for controlling the entire image forming apparatus 100 together with the image forming unit 110 .

The control unit 20 implements various functions by reading and executing various programs, and is composed of, for example, one or a plurality of arithmetic units (for example, CPU (Central Processing Unit)).

Image input unit 130 is a functional unit for inputting image data to be input to image forming apparatus 100 . Image input section 130 is connected to image reading section 90 for reading an image of a document, and receives image data output from image reading section 90 .

Also, the image input unit 130 may input image data from a storage medium such as a USB memory or an SD card. Also, image data may be input from another terminal device by a communication unit (not shown) that connects with the other terminal device.

The image reading unit 90 has a function of optically reading a document placed on a contact glass (not shown) or the like of the document placing table 92 and passing the read data to the image processing unit 140 .

The image processing unit 140 has an image processing function of converting image data input from the image input unit 130 into a set file format (TIFF, GIF, JPEG, etc.). Then, an output image is formed based on the image data subjected to image processing.

The operation unit 150 is a functional unit for receiving operation instructions from the user, and includes various key switches, a device for detecting input by contact, and the like. The user inputs functions to be used and output conditions via the operation unit 150 .

The display unit 160 is a functional unit for displaying various information to the user, and is configured by, for example, an LCD (Liquid crystal display).

The storage unit 170 is a functional unit that stores various programs including control programs necessary for the operation of the image forming apparatus 100, various data including read data, and user information. The storage unit 170 includes, for example, a nonvolatile ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), and the like. Also, an SSD (Solid State Drive), which is a semiconductor memory, may be provided.

The communication unit 180 establishes a communication connection with an external device. A communication interface (communication I/F) used for data transmission/reception is provided as the communication unit 180 . Through the communication I/F, the data stored in the storage unit 170 of the image forming apparatus 100 can be transmitted and received to other computer devices connected via the network by the user's operation on the image forming apparatus 100 .

[1.4 Control and operation]
FIG. 3 is an explanatory diagram of the intermediate transfer belt unit 6 in the image forming apparatus.
Control and operation of the intermediate transfer belt unit 6 will be described.

The image forming apparatus 100 has a mechanism that keeps the intermediate transfer belt 61 in contact with the photosensitive drum 3 during toner image transfer and separates it from the photosensitive drum 3 except during image transfer. It has a function of bringing the intermediate transfer roller 64 closer to or away from the photoreceptor drum 3 by means of an actuator such as an actuator, and bringing the photoreceptor drum 3 into contact with or away from the intermediate transfer belt 61 .

When the image forming apparatus 100 is in a stopped state, as shown in FIG. It is in a state where it does not come into contact with 3. In other words, the space between the intermediate transfer belt 61 and the photosensitive drum 3 is in a "separated state" in which no gap or nip pressure is applied. Due to the "separated state", the intermediate transfer belt 61 is stretched between the intermediate transfer belt drive roller 62 and the intermediate transfer belt driven roller 63, and is loose between the photosensitive drum 3 and the intermediate transfer roller 64. ing.

On the other hand, in the preparation stage of the image forming process, as shown in FIG. ), the intermediate transfer belt 61 is brought into contact with the photoreceptor drum 3 with a predetermined nip pressure. I have to. As shown in the figure, the intermediate transfer belt drive roller 62 and each photosensitive drum 3 are rotationally driven in the direction of the arc arrow.

[Premise]
Here, in order to extend the life of the intermediate transfer belt 61 (life until replacement time), the tension of the intermediate transfer belt 61 may be lowered in the "separated state" as described above. While printing one to several sheets, the intermediate transfer belt 61 between the photoreceptor drums 3 remains flexed. Change. If this slight change in belt speed is not dealt with, it appears in printing as color deviation in the transport direction, and color deviation in the transport direction occurs on the first to several sheets of printing of a plurality of sheets.

The embodiment has the following configuration in order to prevent color misregistration at the start of printing.

In the image forming apparatus according to the embodiment, the controller 20 causes the intermediate transfer belt unit 6 to contact the photosensitive drums 3 (3Y, 3M, 3C, and 3BK) before the image forming process. is controlled to stabilize the conveying speed of the intermediate transfer belt 61 by controlling the rotational speed of the photosensitive drum 3 to a speed different from the normal rotational speed.

A description will be given of control to make the conveying speed of the photosensitive drum 3 slower than the conveying speed of the intermediate transfer belt drive roller 62 (: Example 1) and control to make it faster (: Example 2).

The steady rotation speed of the photoreceptor drum 3 is such that the conveying speed of the intermediate transfer belt 61 is stable and the conveying speed of the intermediate transfer belt by the intermediate transfer belt drive roller 62 matches the conveying speed of the photoreceptor drum 3 . This is the speed at which the intermediate transfer belt 61 is conveyed without deviation.

Next, the behavior of the intermediate transfer belt 61 from contact of the intermediate transfer belt 61 with the photosensitive drum 3 to stabilization of the conveying speed of the intermediate transfer belt 61 in Examples 1 and 2 will be described with reference to FIGS. 4 to 7. FIG. A bent portion of the intermediate transfer belt 61 is indicated by a dashed line portion with reference numeral “Df”.

[Embodiment 1: Conveyance speed of intermediate transfer belt driving roller 62>Conveyance speed of photoreceptor drum 3]
The behavior of the intermediate transfer belt when the control of the first embodiment is performed will be described with reference to FIGS. 4 and 5. FIG.

Immediately after the photosensitive drum 3 abuts the intermediate transfer belt 61, the intermediate transfer belt 61 is bent as shown in FIG. 4(a). The places where there is flexure are between the intermediate transfer belt drive roller 62 and the intermediate transfer belt driven roller 63 and are the places where the photosensitive drums 3 (3Y, 3M, 3C, 3BK) are conveyed.

In the portion where the intermediate transfer belt 61 is bent, the sheet is conveyed according to the conveying speed of the photosensitive drum 3 instead of the speed of the intermediate transfer belt driving roller 62 .

In the first embodiment, the conveying speed of the intermediate transfer belt driving roller 62 >the conveying speed of the photosensitive drum 3 is controlled. As indicated by the arrows in FIG. 4A, the intermediate transfer belt 61 receives a force in the advancing direction by the intermediate transfer belt driving roller 62, and a force in the lagging direction at the portion sandwiched between the photosensitive drums 3. FIG. The intermediate transfer belt 61 slows down in the flexed portion.

In the intermediate transfer belt 61, the transport speed of the photosensitive drum 3 has a transport speed difference that is slower than the transport speed of the intermediate transfer belt driving roller 62. Therefore, if the transport is continued, as shown in FIG. In addition, the intermediate transfer belt 61 on the downstream side of the black (BK) photosensitive drum 3BK is pulled by the intermediate transfer belt driving roller 62, and the black photosensitive drum BK and the intermediate transfer belt driving roller 62 are pulled. Flexion is eliminated in between.

Subsequently, when the conveyance is continued, as shown in FIG. 4C, in the intermediate transfer belt 61, the bending between the black photoconductor drum 3BK and the cyan (C) photoconductor drum 3C causes the photoconductor drum 3BK to bend. And the intermediate transfer belt drive roller 62 is conveyed to eliminate the problem.

Subsequently, when the conveyance is continued, as shown in FIG. 5A, in the intermediate transfer belt 61, the flexure between the cyan (C) photosensitive drum 3C and the magenta (M) photosensitive drum 3M is The transfer of the body drum 3C, the upstream drum 3BK, and the intermediate transfer belt driving roller 62 eliminates the problem.

Subsequently, when the conveyance is continued, as shown in FIG. 5B, in the intermediate transfer belt 61, the bending between the magenta (M) photosensitive drum 3M and the yellow (Y) photosensitive drum 3Y is caused by the photosensitive drum 3Y. The transfer of the body drum 3M, the photosensitive drums 3C and 3BK on the upstream side thereof, and the intermediate transfer belt driving roller 62 eliminates the problem.

Ultimately, the intermediate transfer belt 61 conveyed by each of the photosensitive drums 3 (3Y, 3M, 3C, 3BK) becomes unbent and matches the conveying speed of the intermediate transfer belt driving roller 62. FIG.

FIG. 5(c) shows the speed change of the intermediate transfer belt 61 when the control of the first embodiment is performed. Since the conveying speed of the photosensitive drum 3 is made slower than that of the intermediate transfer belt 61 , the intermediate transfer belt 61 , which was flexed at first, gradually loses the flexure and coincides with the conveying speed of the intermediate transfer belt drive roller 62 . understood.

[Embodiment 2: Conveyance Speed of Intermediate Transfer Belt Drive Roller 62 <Conveyance Speed of Photoreceptor Drum 3]
Behavior of the intermediate transfer belt when the control of the second embodiment is performed will be described with reference to FIGS. 6 and 7. FIG.

Immediately after the photosensitive drum 3 abuts the intermediate transfer belt 61, the intermediate transfer belt 61 is bent as shown in FIG. 6(a). The places where there is flexure are between the intermediate transfer belt drive roller 62 and the intermediate transfer belt driven roller 63 and are the places where the photosensitive drums 3 (3Y, 3M, 3C, 3BK) are conveyed.

In the portion where the intermediate transfer belt 61 is bent, the sheet is conveyed according to the conveying speed of the photosensitive drum 3 instead of the speed of the intermediate transfer belt driving roller 62 .

In the second embodiment, the conveying speed of the intermediate transfer belt driving roller 62<the conveying speed of the photosensitive drum 3 is controlled. As indicated by the arrows in FIG. 6A, the intermediate transfer belt 61 receives a force in the delay direction from the intermediate transfer belt drive roller 62 via the intermediate transfer belt driven roller 63, and the portion sandwiched between the photosensitive drums 3 is applied. A force is applied in the forward direction. The intermediate transfer belt 61 speeds up at the bent portion.

In the intermediate transfer belt 61, the photoreceptor drum 3 has a difference in transport speed that is faster than the transport speed of the intermediate transfer belt driving roller 62. Therefore, if the transport is continued, as shown in FIG. A pulling force from the photosensitive drum 3Y is applied to the intermediate transfer belt 61 on the upstream side of the Y) photosensitive drum 3Y, and bending between the yellow photosensitive drum 3Y and the intermediate transfer belt driven roller 63 is eliminated. .

Next, when the conveyance is continued, as shown in FIG. 6C, in the intermediate transfer belt 61, the bending between the yellow photosensitive drum 3Y and the magenta photosensitive drum 3M is caused by the conveyance of the photosensitive drum 3M. being canceled.

Next, when the conveyance is continued, as shown in FIG. 7A, in the intermediate transfer belt 61, the bending between the magenta photosensitive drum 3M and the cyan photosensitive drum 3C is caused by the conveyance of the photosensitive drum 3C. being canceled.

Next, when the conveyance is continued, as shown in FIG. 7B, in the intermediate transfer belt 61, the bending between the cyan photosensitive drum 3C and the black photosensitive drum 3BK is caused by the conveyance of the photosensitive drum 3BK. being canceled.

Ultimately, the intermediate transfer belt 61 conveyed by each of the photosensitive drums 3 (3Y, 3M, 3C, 3BK) becomes unbent and matches the conveying speed of the intermediate transfer belt driving roller 62. FIG.

FIG. 7(c) shows the speed change of the intermediate transfer belt 61 when the control of the second embodiment is performed. Since the conveying speed of the photosensitive drums 3 is faster than that of the intermediate transfer belt 61, the speed of the photosensitive drums 3 with the initial deflection is gradually eliminated, and the conveying speed of the intermediate transfer belt drive roller 62 is increased. It is understood that the point coincides with steady state speed.

FIG. 8 is a diagram for explaining color misregistration in the sub-conveying direction with respect to changes in speed of the intermediate transfer belt.
As shown in FIG. 8A, the photosensitive drums 3 of each color are arranged in order of 3Y, 3M, 3C, and 3BK.

As shown in FIG. 8B, when the intermediate transfer belt 61 is at a constant speed, the BK, C, M, and Y toners overlap at the same positions.

As shown in FIG. 8C, when the speed of the intermediate transfer belt 61 is faster than the normal speed, C, M, and Y have already passed BK at the drawing timing of BK. C, M, and Y are color-shifted toward the leading edge of the paper with respect to BK.

As shown in FIG. 8D, when the speed of the intermediate transfer belt 61 is slower than the normal speed, C, M, and Y have not reached BK at the drawing timing of BK. C, M, and Y are color-shifted toward the trailing edge of the paper with respect to BK.

FIG. 9 shows color shift data in the BK phase in the sub-scanning direction. This is color misregistration data when printing the first to third sheets.

As shown in FIG. 9, when the speed of the photoreceptor drum 3 is set to -0.1% (reduced) with respect to the steady speed, color misregistration occurs from the first multi-sheet to the second and third multi-sheets. decreases and the deviation disappears. In this case, the speeds of all the Y, M, C, and BK photosensitive drums 3 are made slower than the speed of the intermediate transfer belt drive roller 62 in the steady state.

Further, when the speed of the photoreceptor drum 3 is ±0% with respect to the steady speed, the color misregistration decreases and disappears as the first, second, and third multi-sheets are printed. .

Further, when the speed of the photosensitive drum 3 is increased by +0.1% with respect to the steady speed, the color misregistration decreases from the first multi-sheet to the second and third sheets. In this case, the speeds of all the Y, M, C, and BK photosensitive drums 3 are set higher than the speed of the intermediate transfer belt driving roller 62 in the steady state.

[2. Second Embodiment]
As shown in FIG. 10(a), the image forming apparatus according to the second embodiment is the same as that of the first embodiment in which the photosensitive drums 3Y, 3M, 3C, and 3BK are arranged in order. Within the time from when the intermediate transfer belt 61 comes into contact with the photosensitive drums 3BK, 3C, 3M, and 3Y of the respective colors BK, C, M, and Y until the unit 20 starts image formation (drawing starts with the LSU). In addition, control (referred to as "deflection suppression control") is performed to provide a difference in the speed of the photosensitive drums 3BK, 3C, 3M, and 3Y so as to stretch the intermediate transfer belt 61. FIG.

The controller 20 increases the rotation speed of the photosensitive drums 3BK, 3C, 3M, and 3Y from the upstream side to the downstream side of the intermediate transfer belt.

As a result, the bending of the intermediate transfer belt 61 is quickly eliminated, and the time required for image formation is shortened.

Specifically, during the time from the contact between the intermediate transfer belt 61 and the photosensitive drums 3 to the start of LSU drawing, the photosensitive drums 3BK, 3C, 3M, and 3Y of the colors BK, C, M, and Y are stretched so as to stretch the belt. (=change the clock CLK frequency of the driving motor).

Regarding the speed of each color photoreceptor drum 3, the Y photoreceptor drum 3Y is set to -0.75% of the normal speed (reduced), and the M photoreceptor drum 3M is set to -0.25% of the normal speed (reduced). , and C photosensitive drums 3C are set to +0.25% of the steady speed (increased), and the photosensitive drums 3C and BK are set to +0.75% of the steady speed (increased).

In this manner, the control unit 20 keeps the speed difference between the adjacent photosensitive drums 3BK, 3C, 3M, and 3Y constant, such as increasing by 0.5% in order.

As shown in FIG. 10(b), the speed is controlled by controlling the clock frequency of the driving motors of the photosensitive drums 3Y, 3M, 3C and 3BK. The velocities of the photosensitive drums 3Y, 3M, 3C, and 3BK are changed immediately before they come into contact with the intermediate transfer belt 61, and are returned to a constant velocity immediately before the Y LSU (laser scanning unit) starts drawing. .

FIG. 11 shows a comparison between the belt deflection suppression control of the second embodiment and the control of the first embodiment in which such belt deflection suppression control is not performed until printing becomes possible. A flexed portion of the intermediate transfer belt 61 is indicated by a broken line portion denoted by reference numeral “Df”.

As shown in FIG. 11, in the second embodiment (deflection suppression control), in period 1, immediately after the photosensitive drums 3BK, 3C, 3M, and 3Y come into contact with the intermediate transfer belt 61, the entire intermediate transfer belt 61 is Flexion remains.

After that, when it is conveyed, the flexure of the intermediate transfer belt 61 between the photosensitive drums 3BK, 3C, 3M, and 3Y is eliminated in period 2, and between the intermediate transfer belt drive roller 62 and the photosensitive drum 3BK, The bending of the intermediate transfer belt 61 remains between the intermediate transfer belt driven roller 63 and the photosensitive drum 3Y (NG). In the figure, the portion surrounded by the dashed line Df indicates the bending portion.

After that, in the period 3, the intermediate transfer belt 61 is no longer flexed between the intermediate transfer belt driving roller 62 and the BK photosensitive drums 3BK, so that the transfer roller 10 and the respective BK, C, M, and Y photosensitive drums 3BK, The velocities of 3C, 3M, and 3Y become steady velocities, and the velocities are stabilized. Therefore, since the speed is stabilized quickly, color misregistration does not occur even if the rotation time before printing is short (OK). Printing can be started in the OK area without color shift.

On the other hand, in the control of Example 1 of the first embodiment, immediately after the photosensitive drums 3BK, 3C, 3M, and 3Y come into contact with the intermediate transfer belt 61 in period 1, The deflection between the transfer belt drive roller 62 and the BK photosensitive drum 3BK is eliminated. Next, in period 3, the bending between the photoreceptor drums 3BK and C photoreceptor drums 3C disappears. Next, in period 4, the bending between the photoreceptor drum 3C and the photoreceptor drum 3M disappears. Bending remains (NG). After that, in period 5, the deflection between the photoreceptor drums 3M and Y photoreceptor drums 3Y finally disappears, the speed of the intermediate transfer belt 61 stabilizes, and the color misregistration disappears (OK).

Therefore, in the first embodiment, it takes a long time to eliminate the warp in the periods 1 to 4, but in the second embodiment, the warp disappears after the period 1 and the period 2, and printing can be started in a short period of time after startup. understood.

FIG. 12 shows data comparing the color shifts of Y, M, and C with respect to the BK phase in the first embodiment and the second embodiment. FIG. 12(a) shows the color misregistration data of the first embodiment, and FIG. 12(b) shows the color misregistration data of the second embodiment.

In FIG. 12, in the first embodiment and the second embodiment, when the speed of the photosensitive drums 3BK, 3C, 3M, and 3Y is slowed down to -0.1% and ±0%, +0. Each color misregistration (for multi-printing, for example, three-sheet printing) is shown when speed is increased to 1% (similar to FIG. 9).

Specifically, in the second embodiment, when the speed of each photosensitive drum 3 of Y, M, C, and BK is "drum ±0%", Y: -0.75% M: -0.25% C: +0.25% BK: +0.75%.
In the case of "drum -0.1%", Y: -0.75%-0.1% M: -0.25%-0.1% C: +0.25%-0.1% BK: +0.75%-0.1%, "drum +0.1%" The same is true for the case of
Therefore, as shown in FIG. 12(a), in the first embodiment, the color misregistration is eliminated after the third multi-sheet, but as shown in FIG. 12(b), in the second embodiment, only one multi-sheet is printed. Stable with no color deviation from the eye.

Therefore, since it takes periods 1 to 5 until the speed of the intermediate transfer belt 61 stabilizes, the rotation time before printing is lengthened, or printing is performed in a state where color misregistration occurs. Therefore, in the second embodiment, the time required for the intermediate transfer belt 61 to stabilize is shorter than in the first embodiment, and printing can be started at high speed.

[3. Third Embodiment]
13 to 15 are explanatory diagrams of the third embodiment. In FIG. 13, the flexing portion of the intermediate transfer belt 61 is indicated by the dashed line portion with reference numeral "Df".

In the third embodiment, the control unit 20 performs the deflection suppression control described in the second embodiment, and furthermore, as the machine life of the image forming apparatus elapses, the speed changes of the photosensitive drums 3BK, 3C, 3M, and 3Y increase. It is the speed of the average value of the amount.

As shown in FIG. 13, the intermediate transfer belt driving roller 62>photosensitive drum 3 speed control is performed at the beginning of the life, and the speed control shifts to the intermediate transfer belt driving roller 62<photosensitive drum 3 at the latter half of the life. is.

The speed of the intermediate transfer belt 61 is determined by the speed of the intermediate transfer belt drive roller 62 . Since the diameter of the intermediate transfer drive roller 62 is reduced as it wears out over the course of its life, its speed gradually decreases. Therefore, the speed of the intermediate transfer belt 61 becomes intermediate transfer belt driving roller 62>photosensitive drum 3 at the beginning of its life, and shifts to intermediate transfer belt driving roller 62<photosensitive drum 3 at the latter half of its life.

Deflection control of the third embodiment will be described with reference to FIG. At the beginning of the life, the intermediate transfer belt 61 is bent as a whole immediately after contact in period 1 . In period 2, the intermediate transfer belt 61 between the photosensitive drums 3BK, 3C, 3M, and 3Y is no longer flexed, and the photosensitive drum 3BK and the intermediate transfer belt driving roller 62, and the photosensitive drum 3Y and the intermediate transfer belt driven roller 63 are in contact with each other. Flexion occurs between them.

In the final period 3, the deflection between the downstream of the photosensitive drum BK and the intermediate transfer drive roller 62 (indicated by symbol Df) is in the direction of the arrow due to the speed difference between the downstream of the photosensitive drum BK and the intermediate transfer drive roller 62. Since it is pulled, the bending disappears.

Therefore, at the beginning of the life of the drum, if the amount of drum speed change by deflection control is slowed down (by controlling it to be slowed down), the deflection will be eliminated more quickly.

On the other hand, in the latter half of the life, period 1 and period 2 are the same as the initial period, but in the final period 3, the deflection (indicated by Df) between the upstream of the photosensitive drum Y and the intermediate transfer belt driven roller 63 is exposed. Since it is pulled in the direction of the arrow by the speed difference between the upstream of the body drum Y and the intermediate transfer driven roller 63, the deflection is eliminated.

Therefore, in the latter half of the life, the deflection can be eliminated more quickly by increasing the drum speed change amount by deflection control (by controlling the drum speed to be increased).

Deflection control of the third embodiment will be specifically described. As shown in FIG. 14A, in the transfer unit 3 of the image forming apparatus, the voltage clock of the drive motor (drum motor) for the photosensitive drums 3BK, 3C, 3M, and 3Y of each color BK, C, M, and Y is The speed is controlled by changing the frequency.

At the early stage of life, as shown in FIG. late. As a whole, the speed control of "the speed of the intermediate transfer belt driving roller 62>the photosensitive drum 3" is achieved.

In the latter half of the life, as shown in FIG. 14(c), the speed of the photosensitive drums 3BK, 3C, and 3M is increased, and the speed of the photosensitive drum 3Y is decreased. As a whole, the speed control of "the speed of the intermediate transfer belt driving roller 62<the photosensitive drum 3" is achieved.

As a more specific numerical example, as shown in FIG. 15, the life was measured according to the number of printed sheets (in the figure, "k" indicates 1000 sheets). From the start of printing, from the first printed sheet to the 999k sheet, the average value of the acceleration rate of the drum motors of the photosensitive drums 3BK, 3C, 3M, and 3Y for each color BK, C, M, and Y: [-0.4% (= -1.2%/3)].

The average value of the acceleration rate of the drum motor is [-0.2% (=-0.6%/3)] when the number of printed sheets is from 1000k to 1999k.

The average value of the acceleration rate of the drum motor is [±0% (=±0%/3)] when the number of printed sheets is from 2000k to 2999k.

The average value of the acceleration rate of the drum motor is [0.2% (=0.6%/3)] when the number of printed sheets is 3000k to 3999k.

The average value of the acceleration rate of the drum motor for the number of printed sheets of 4000 k or more is [0.4% (=1.2%/3)].

Therefore, the average value of the speed increasing rate increases, and the speed is increased as the life elapses, so that the deflection of the intermediate transfer belt is eliminated more quickly.

[4. Fourth Embodiment]
In the fourth embodiment, the controller 20 increases the amount of change in speed of each of the photosensitive drums 3BK, 3C, 3M, and 3Y as the machine life elapses. During the printing operation, the intermediate transfer belt 61 is stretched by applying tension. Therefore, the circumference of the belt gradually increases with the lapse of life. Therefore, since the amount of deflection of the intermediate transfer belt 61 increases with the lapse of life, the amount of change in speed is increased to eliminate the deflection.

As shown in FIG. 16(a), the controller 20 controls the speed change amount of the photosensitive drums 3BK, 3C, 3M, and 3Y of the respective colors BK, C, M, and Y to be small at the beginning of the life, and , and as shown in FIG. 16(b), the amount of change in measure of the photosensitive drums 3BK, 3C, 3M, and 3Y of each color BK, C, M, and Y is increased.

FIG. 16(c) shows an example of the amount of speed change due to life.

After starting printing, from the first printed sheet to 999k sheets, the acceleration rate of the drum motors of the photosensitive drums 3BK, 3C, 3M, and 3Y for each color BK, C, M, and Y is [0.60%, 0.20% - 0.20% ,-0.60%].

From 1000k to 1999k printed sheets, the acceleration rates of the drum motors of the photosensitive drums 3BK, 3C, 3M and 3Y are [0.66%, 0.22%, -0.22%, -0.66%].

From the 2000k to 2999k printed sheets, the acceleration rates of the drum motors of the photosensitive drums 3BK, 3C, 3M, and 3Y are [0.73%, 0.24%, -0.24%, -0.73%].

From 3000k to 3999k printed sheets, the acceleration rates of the drum motors of the photosensitive drums 3BK, 3C, 3M, and 3Y are [0.80%, 0.27%, -0.27%, -0.80%].

From the 4000th printed sheet, the acceleration rate of the drum motors of the photosensitive drums 3BK, 3C, 3M and 3Y is [0.88%, 0.29%.-0.29%, -0.88%].

The drum 3Y at the end on the upstream side and the drum 3BK at the end on the downstream side change the speed increasing rate more greatly than the drums 3C and 3M on the center side.

It can be understood that even if the bending of the intermediate transfer belt 61 increases as the life of the intermediate transfer belt 61 elapses, the bending can be effectively eliminated by increasing the amount of change in speed.

Although the embodiment has been described above, the specific configuration is not limited to the embodiment, and designs and the like without departing from the gist of the present invention are also included in the scope of claims.

Also, in the embodiments, the programs that operate on each device are programs that control CPUs and the like (programs that cause computers to function) so as to implement the functions of the above-described embodiments. The information handled by these devices is temporarily stored in a temporary storage device (for example, RAM) during processing, then stored in various ROM and HDD storage devices, read out by the CPU as necessary, corrected, and processed. Writing is done.

Examples of recording media for storing programs include semiconductor media (eg, ROM, nonvolatile memory cards, etc.), optical recording media/magneto-optical recording media (eg, DVD (Digital Versatile Disc), MO (magneto Optical Disc), Non-temporary recording media such as (MD (Mini Disc), CD (Compact Disc), BD (Blu-ray (registered trademark) Disc), etc.), magnetic recording media (e.g., magnetic tape, flexible disc, etc.) Either is fine.

Also, by executing the loaded program, not only can the functions of the above-described embodiments be realized, but also by processing in cooperation with the operating system or other application programs, etc., based on the instructions of the program, the present invention can be realized. In some cases, the disclosed functions are implemented.

When the program is distributed in the market, the program can be distributed by storing it in a portable storage device, or transferred to a server computer connected via a network such as the Internet. In this case, of course, the storage device of the server computer is also included in the present invention.

Also, part or all of the devices in the above-described embodiments may be typically implemented as an LSI (Large Scale Integration), which is an integrated circuit. Each functional block of each device may be individually chipped, or part or all of them may be integrated and chipped. Also, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. In addition, it is of course possible to use an integrated circuit based on this technology when an integrated circuit technology that replaces LSI emerges due to advances in semiconductor technology.

3 (3BK, 3C, 3M) Photoreceptor drum 6 Intermediate transfer belt unit 10 Transfer roller 100 Image forming device 20 Control section 61 Intermediate transfer belt 62 Intermediate transfer belt driving roller 63 Intermediate transfer belt driven roller 64 Intermediate transfer roller 100 Image forming device 110 image forming unit

Claims (7)

an image forming unit that forms an image on a predetermined sheet by electrophotography; and a control unit that controls the image forming unit,
The image forming unit
a developer that develops a plurality of photoreceptor drums to form toner images of different colors;
a drive system that independently drives the plurality of photoreceptor drums;
an intermediate transfer belt on which toner images of respective colors are transferred in contact with the plurality of photoreceptor drums;
a mechanism for bringing the intermediate transfer belt into contact with the photosensitive drum during toner image transfer and separating from the photosensitive drum except during image transfer; and a secondary transfer unit for transferring the toner image on the intermediate transfer belt to paper. , and
The controller is characterized in that the rotation speed of the photoreceptor drum is set to a speed different from the normal rotation speed from when the intermediate transfer belt is brought into contact with the photoreceptor drum until the image forming process is started. image forming device. 2. The image forming apparatus according to claim 1, wherein the control section controls the rotational speeds of the respective photosensitive drums to different speeds until the image forming process is started. 3. The image forming apparatus according to claim 2, wherein the controller speeds up the rotation speed of the photosensitive drum from the upstream side to the downstream side of the intermediate transfer belt. 4. The image forming apparatus according to claim 1, wherein the controller keeps a speed difference between adjacent photosensitive drums constant. 5. The image forming apparatus according to claim 1, wherein the control unit increases the average value of the speed change amount of each photosensitive drum as the machine life elapses. 5. The image forming apparatus according to any one of items 1 to 4, wherein the controller increases the amount of change in velocity of each photosensitive drum as the machine life elapses. a step of independently driving a plurality of photoreceptor drums;
a step of bringing the intermediate transfer belt into contact with the photosensitive drum when transferring an image to the intermediate transfer belt, and separating the intermediate transfer belt from the photosensitive drum except when transferring an image;
a secondary transfer step of transferring the toner image on the intermediate transfer drum to a sheet;
a control step of controlling a drive system of the image forming unit;
The control step is characterized in that the rotation speed of the photoreceptor drum is set to a speed different from the normal rotation speed from the time when the intermediate transfer belt is brought into contact with the photoreceptor drum until the image forming process is started. image forming apparatus control method.

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