JPH11311886A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of performing satisfactory fixing, in the case of forming a full color image with respect to material paper such as a thick paper, an OHP sheet, a surface coated paper or the like. SOLUTION: This device is, when a start key is operated in the case a special mode is set (step S11), allowed to start a primary transfer operation (step S12). At the point of time when it is judged that the primary transfer operation is completed (step S13), the device is allowed to separate a transfer belt from a photoreceptor periphery by shifting a primary transfer upper roller, and to set a paper feed/transporting system and a discharge paper transporting system at the special paper transporting speed (step S14), and then to start a secondary operation (step S15).

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, and more particularly, to a method of forming a toner image for each color component of a document image on a photosensitive drum, transferring the toner image to an intermediate transfer member, and forming the image on the intermediate transfer member. The present invention relates to an image forming apparatus for further transferring a color toner image in which respective color components are stacked on a conveyed sheet.

[0002]

2. Description of the Related Art Some image forming apparatuses such as copiers and printers form a color image on paper by superposing a plurality of kinds of color toners. For example, in a full-color copying machine, an image reading unit that reads a document image, an image processing unit that separates the read document image into four color components of cyan, magenta, yellow, and black, and an electrostatic latent image is formed on the peripheral surface Photosensitive drum, an exposure unit for forming an electrostatic latent image for each color component on the peripheral surface of the photosensitive drum, and visualizing the electrostatic latent image formed on the photosensitive drum with a corresponding color toner. Four developing devices, a transfer belt on which toner images formed on the photosensitive drum are sequentially transferred to form a stacked color toner image, and a color toner image transferred on the transfer belt to be transferred onto paper 2 Some include a next transfer roller and a fixing device for heating and fusing and fixing the color toner image on the sheet.

The read original image is cyan, magenta,
First, an electrostatic latent image corresponding to cyan is formed on the peripheral surface of the photosensitive drum. The electrostatic latent image formed on the peripheral surface of the photosensitive drum is visualized by a developing device containing cyan toner, and the cyan toner image is transferred to the surface of the transfer belt. Thereafter, similarly, magenta, yellow, and black toner images are formed on the peripheral surface of the photosensitive drum and transferred to the transfer belt. As a result, toner images of each color are stacked on the surface of the transfer belt to form a color toner image.

Thereafter, the sheet is conveyed between the transfer belt and the secondary transfer roller, and the color toner image on the surface of the transfer belt is transferred onto the sheet by the secondary transfer roller. The sheet on which the color toner image has been transferred is further transported to the fixing device. The fixing device is provided with a heating roller having a built-in heater and a pressure roller that presses against the heating roller. The sheet is sandwiched between the heating roller and the pressure roller to melt and fix the color toner image and to fix the sheet. In the discharge direction.

When an image is formed on a so-called material paper such as a thick paper, an OHP sheet, or a surface-coated paper having a coated surface in the image forming apparatus having the above-described configuration, the heat capacity of the paper is required. The paper that arrives at the fixing device quickly takes away the heat of the heating roller due to the large size of the heat roller, and the heat of the heating roller is properly transmitted to the paper because the nip width between the heating roller and the pressure roller is not sufficient. The inability to do so may result in improper fusion and fixing of the toner. This is a phenomenon that can occur even in a single-color image forming apparatus. In particular, in the case of an image forming apparatus that forms a full-color image, a color toner image in which a plurality of single-color toner images are stacked as described above is used. Since it is formed on paper and has a thicker toner layer than a normal single-color toner image, there is a strong possibility that proper fixing will not be performed unless heating in the fixing device is sufficient.

In order to solve such a problem, when forming an image on material paper such as a thick paper or an OHP sheet, the paper conveying speed of the fixing device is set to be lower than that for forming an image on normal paper. It can be considered that the toner is sufficiently fused and fixed.

[0007]

In the above-described image forming apparatus, depending on the paper size on which the image is formed,
When the leading edge of the conveyed paper reaches the fixing unit, the rear end of the paper may not pass between the transfer belt and the secondary transfer roller. In such a case, if the conveyance speed of the fixing device is set lower than the normal conveyance speed, the paper may bend between the secondary transfer roller and the fixing device, and a paper jam may occur. For this reason, when the conveyance speed of the fixing device is reduced for such a material sheet, 2
It is conceivable to reduce the speed of the next transfer roller and the transfer belt in synchronization with the speed of the fixing device. However, since the transfer belt is pressed against the peripheral surface of the photosensitive drum by the primary transfer roller, relative slippage occurs between the transfer belt and the photosensitive drum, and the surfaces of the photosensitive drum and the transfer belt may be damaged. . It is conceivable to reduce the rotation speed of the photoconductor drum in accordance with this. However, since the rotation speed of the photoconductor drum is synchronized with the exposure unit that forms an electrostatic latent image on the photoconductor drum, the rotation speed of the photoconductor drum is changed. It is not preferable.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of performing sufficient fixing when forming a full-color image on a material paper such as a thick paper, an OHP sheet, and a surface coated paper.

[0009]

An image forming apparatus according to the present invention comprises a photosensitive drum, an exposing means, a developing means, an intermediate transfer member, a primary transfer means, a secondary transfer means, and a fixing means. , Special paper setting means, and special paper transfer control means. The exposing means forms an electrostatic latent image on the peripheral surface of the photosensitive drum according to the color components of the image to be formed. The developing unit visualizes the electrostatic latent image formed on the peripheral surface of the photoconductor drum into a toner image using a corresponding color toner. On the intermediate transfer member, a color toner image formed by transferring the toner image formed on the surface of the photosensitive drum and laminating the toner image is formed on the surface. The primary transfer means is movable between a position where the intermediate transfer member is pressed against the peripheral surface of the photosensitive drum and a position where the intermediate transfer member is separated from the peripheral surface of the photosensitive drum, and is formed on the peripheral surface of the photosensitive drum. The transferred toner image is transferred to the surface of the intermediate transfer member. The secondary transfer unit transfers the color toner image formed on the intermediate transfer member to a sheet that is pressed against the intermediate transfer member and conveyed to the intermediate transfer member. The fixing unit has a heating roller with a built-in heater, and a pressure roller that presses against the heating roller,
The sheet on which the color toner image has been transferred is nipped and conveyed, and the color toner image is heated and fixed. The special paper setting unit sets each unit to a special paper mode in which an image is formed on the special paper. When the special paper mode is set by the special paper mode setting means, the special paper transfer control means causes the intermediate transfer body to rotate around the photosensitive drum at least when the color toner image on the intermediate transfer body by the primary transfer means ends. The primary transfer unit is moved away from the surface, and the fixing unit, the secondary transfer unit, and the intermediate transfer body are driven at a special paper transport speed lower than the normal transport speed.

In the case of such a configuration, thick paper, OH
When performing image formation on a so-called material paper such as a P sheet or a surface coated paper, each unit is set to a special paper mode by a special paper setting unit. The photoconductor drum and the intermediate transfer member are driven to rotate at a normal speed, and a color toner image in which toner images of respective color components are laminated on the surface of the intermediate transfer member is formed. Thereafter, the sheet is transported between the secondary transfer means and the intermediate transfer member, and the color toner image is transferred onto the sheet. When the transfer of the color toner image to the intermediate transfer body by the primary transfer means is completed, the pressure contact of the intermediate transfer body to the photosensitive drum by the primary transfer means is released, and the fixing means, the intermediate transfer body and the secondary The transfer speed of the transfer unit is set to a special paper transfer speed lower than the normal transfer speed. Thus, when an image is formed on a material paper such as a thick paper, an OHP sheet, or a surface-coated paper, the toner transferred onto the paper can be sufficiently melt-fixed by the fixing unit, and the photosensitive drum and the intermediate transfer It is possible to prevent the photosensitive drum and the surface of the intermediate transfer member from being damaged due to relative sliding with the body. When the transfer of the toner image from the photosensitive drum to the intermediate transfer member is completed, and the conveyance of the sheet between the intermediate transfer member and the secondary transfer means is started, the intermediate transfer member is separated from the peripheral surface of the photosensitive drum. It is also possible to move the primary transfer means so that the fixing means, the intermediate transfer member, and the secondary transfer means are driven at a special paper transport speed.

Here, a transfer belt stretched between a driving roller and a driven roller can be used as the intermediate transfer member. Further, a primary transfer unit is disposed on the inner peripheral surface side of the transfer belt, and moves between a pressing position where the transfer belt is pressed against the peripheral surface of the photosensitive drum and a separating position where the transfer belt is separated from the photosensitive drum. It can be constituted by a possible primary transfer roller. Further, the primary transfer means includes a primary transfer upper roller and a primary transfer lower roller, and when the special paper mode is set by the special paper setting means, the primary transfer upper roller and the primary transfer roller At least one of them can be configured to be moved to the separated position.

Further, the developing means can be configured to include a plurality of developing devices corresponding to the respective color components. Specifically, the developing means includes four developing devices corresponding to the respective color components of cyan, magenta, yellow and black. Can be configured. further,
The special paper setting means includes a mode setting receiving means, and can be configured to set each unit to the special paper mode when the mode setting receiving means is operated by an operator.
Including a discriminating unit for discriminating whether or not the sheet conveyed to the next transfer unit is a special sheet, and setting each unit to the special sheet mode when the discriminating unit determines that the sheet is the special sheet. Such a configuration is also possible.

[0013]

FIG. 1 is a cross-sectional view of a full-color copying machine to which an embodiment of the present invention is applied. The copying machine 1 has a main body 10 and a document holder 11 mounted on the upper part of the main body 10 so as to be openable and closable. An original platen 15 on which an original is placed is disposed on the main body 10 at an upper portion thereof. Inside the main body 10, an image forming unit 16 is provided at the left end as viewed from the front and substantially at the center in the vertical direction. Further, a paper feed unit 17 for supplying a document to the image forming unit 16 is provided below.

The paper supply unit 17 is detachably attached to the main body 10 and stores paper supply cassettes 18, 19,
20 and 21, and a bypass tray 22 provided on the right side thereof. Below the platen 15, the platen 1
An optical system 23 for reading image information of a document placed on the document 5 is provided. The optical system 23 includes a light source 24 for irradiating light to the surface of a document placed on the document table 15.
And a mirror 2 for deflecting light reflected from the original surface
5, 26, 27, a lens 28 for converging the light from the mirror 27, and a color imaging device such as a CCD sensor for receiving the light converged by the lens 28 and generating an image data signal corresponding to the original image. 29.

The image forming section 16 has a photosensitive drum 30 on the surface of which an electrostatic latent image is formed.
0, a main charging device 31, a developing device 33,
34, 35, and 36, a transfer device 37, and a cleaning device 38. The main charging device 31 is a device for charging the surface of the photoconductor drum 30, and is disposed above the photoconductor drum 30. Developing devices 33, 34, 35, and 36 that form toner images on the photoconductor drum 30 are arranged from the left side of the photoconductor drum 30 downward from the main charging device 31 with a predetermined gap. Each of the developing devices 33, 34, 35, and 36 stores cyan, magenta, yellow, and black toners, respectively, and visualizes the electrostatic latent image formed on the photosensitive drum 30 by the toner of each color. . The transfer device 37 is a device for transferring the toner image on the photosensitive drum 30 to a sheet, and is disposed diagonally below and to the right of the photosensitive drum 30.
The cleaning device 38 is a device for removing residual toner and the like on the surface of the photoconductor drum 30, and is disposed diagonally above and to the right of the photoconductor drum 30.

An exposure device 39 for forming an electrostatic latent image on the peripheral surface of the photosensitive drum 30 is provided diagonally above and to the left of the photosensitive drum 30. The exposure device 39 includes a laser unit 40 and a mirror 41 that deflects the laser light from the laser unit 40 to the peripheral surface of the photosensitive drum 30. The exposure device 39 rotates the photosensitive drum 30 based on an image data signal obtained from the color image sensor 29. An electrostatic latent image is formed on the surface. The laser light emitted from the exposure device 39 is configured to pass between the main charging device 31 and the developing device 33 and to irradiate the peripheral surface of the photosensitive drum 30. [Transfer Device] As shown in FIG. 2, the transfer device 37 includes a driving roller 44 to which the driving force of the driving motor 42 is transmitted via the driving belt 43, a secondary transfer upper roller 45, and the driving rollers 44 and 2. A transfer belt 46 stretched between the next transfer upper rollers 45; a primary transfer upper roller 47 for pressing the outer peripheral surface of the transfer belt 44 against the peripheral surface of the photosensitive drum 30; a primary transfer lower roller 48; And a tension roller 49 disposed on the inner peripheral surface side of the belt 46.

The upper primary transfer roller 47 and the lower primary transfer roller 48 are located between the drive roller 44 and the upper secondary transfer roller 45, and are connected to the photosensitive drum 30 via a transfer belt 46.
Is disposed at a position opposite to the above. Primary transfer upper roller 4
Numeral 7 is movable between a pressing position where the transfer belt 46 is pressed together with the primary transfer lower roller 48 against the peripheral surface of the photosensitive drum 30 and a separation position where the transfer belt 46 is separated from the peripheral surface of the photosensitive drum 30. ing.

For example, as shown in FIG. 3, the primary transfer roller 47 is rotatably mounted on a mounting plate 50,
The mounting plate 50 is rotatably mounted on the transfer device 37 via the support shaft 51. The mounting plate 50 has a protruding piece 52 protruding downward, and the protruding piece 52 has a primary pressing roller 53 provided in parallel with the rotation axis of the primary transfer upper roller 47.
Is provided. Also. The mounting plate 50 is urged by a spring 54 'in a direction away from the peripheral surface of the photosensitive drum 30.

On the transfer device 37 side, the primary pressing cam 5 having a cam surface capable of contacting the primary pressing roller 53 of the mounting plate 50
4 is movably supported and provided. The driving force of the primary pressing cam drive motor 56 is transmitted to the primary pressing cam 54 by the drive belt 55, and the primary pressing cam 54 is rotatable. A light-shielding plate 57 that rotates integrally with the primary pressing cam 54 is provided on a rotation shaft of the primary pressing cam 54. The light shielding plate 57 has a sector shape in which a part of a circular plate is cut out, and is arranged so as to block an optical path of a transfer belt pressing sensor 58 formed of a photo interrupter.

For example, when the distance of pressing the primary pressing roller 53 on the cam surface of the primary pressing cam 54 is maximized, the upper primary transfer roller 47 presses the transfer belt 46 against the peripheral surface of the photosensitive drum 30. At this time, the transfer belt pressure sensor 58 is shielded from light by the light shielding plate 57 and is turned on at the same time. Also, when the distance of pressing the primary pressing roller 53 on the cam surface of the primary pressing cam 54 is minimized, the upper primary transfer roller 47 is located at a separating position for separating the transfer belt 46 from the peripheral surface of the photosensitive drum 30. And at this time,
The transfer belt pressing sensor 58 is released by the light shielding plate 57 and is turned off.

The transfer device 37 is provided with a zinc stearate coating device 59 for coating the transfer belt 46 with zinc stearate. The zinc stearate coating device 59 includes a zinc stearate coating brush 60 pressed against the drive roller 44 via the transfer belt 46, and a zinc stearate storage unit 61 for supplying zinc stearate to the zinc stearate coating brush 60. It is composed of The zinc stearate coating device 59 is used to transfer the transfer belt 46.
When the toner adhered to the paper is transferred to the surface of the paper, the binding force of the toner to the transfer belt 46 is weakened, and zinc stearate for preventing the toner image formed on the paper from dropping out of the paper is transferred at regular intervals. 46 is applied to the surface. For this reason, the zinc stearate application brush 60 is capable of protruding and retracting with respect to the transfer belt 46, and is configured to be pressed against the drive roller 44 as necessary to apply zinc stearate to the transfer belt 46. ing.

Further, the transfer device 37 includes a transfer belt 4
Cleaning device 6 for cleaning the surface of 6
2 are provided. The cleaning device 62 includes
A cleaning roller 63 disposed between the next lower transfer roller 48 and the upper secondary transfer roller 45 and in contact with the inner peripheral surface side of the transfer belt 46, a cleaning auxiliary roller 64, and a cleaning auxiliary roller via the transfer belt 46 Toner recovery unit 6 having cleaning roller 65 pressed against
6 is provided.

The transfer device 37 includes a transfer belt 46.
And a lower secondary transfer roller 67 that is disposed at a position facing the upper secondary transfer roller 45 through the intermediary of the transfer belt, and applies a voltage having a polarity opposite to that of the toner on the surface of the transfer belt 46 to transfer a toner image onto paper. I have. The secondary transfer lower roller 67 is shown in FIG.
As shown in the figure, the mounting plate 68 is rotatably supported. Further, the secondary transfer lower roller 67 is provided with secondary pressing rollers 69 each having a slightly larger outer diameter and rotating integrally with each other at both ends in the width direction. The outer peripheral surface of the secondary pressing roller 69 comes into contact with the side plate of the transfer device 37,
The positioning is performed so that the peripheral surface of the secondary transfer lower roller 67 and the surface of the transfer belt 46 are at a fixed distance. The distance between the peripheral surface of the secondary transfer lower roller 67 and the surface of the transfer belt 46 is preferably set to the thickness of one sheet.

The mounting plate 68 is movable vertically in FIG. 4, and is urged downward by an urging member (not shown) such as a spring. The mounting plate 68 has a protruding piece 70 protruding downward. The protruding piece 70 is provided with a contact piece 71 protruding in parallel with the rotation axis of the secondary transfer lower roller 67. The contact piece 71 can contact a cam surface of a secondary pressing cam 72 rotatably supported by a side plate of the transfer device 37. The secondary pressing cam 72 is rotatable by a drive motor (not shown), and includes a light shielding plate 73 that rotates integrally. The light shielding plate 73 is configured to be able to take a position where the optical path of the transfer roller pressing sensor 74 constituted by a photo interrupter is shut off and a position where it is opened by rotating.

For example, when the contact piece 71 moved by the cam surface of the secondary pressing cam 72 is located at the uppermost position,
The mounting plate 68 is pushed up most. At this time, 2
The next pressing roller 69 contacts the side plate of the transfer device 37 to position the lower secondary transfer roller 67 at a predetermined position, and the light-shielding plate 73 blocks the optical path of the transfer roller pressing sensor 74 to turn it on. When the contact piece 71 moved by the cam surface of the secondary pressing cam 72 is located at the lowest position,
The mounting plate 68 is positioned at the lowest position by the urging of the urging member. At this time, the lower secondary transfer roller 67 is separated from the surface of the transfer belt 46, and at the same time, the light shielding plate 73 opens the optical path of the transfer roller pressing sensor 74 to be in the off state.

The secondary transfer lower roller 67 is provided with a cleaning blade 75 for removing toner adhering to the peripheral surface in a state of being pressed against the peripheral surface. further,
In the vicinity of the lower secondary transfer roller 67, a separation needle 7 for applying a predetermined voltage to separate the sheet from the transfer belt 46 is applied.
6 are provided. [Sheet Feeding Unit] The sheet feeding unit 17 includes the respective sheet feeding cassettes 18, 1.
A vertical conveyance path 81 for conveying paper from 9, 20, 21 to the image forming unit 16 and a bypass conveyance path 82 for conveying paper from the bypass tray 22 to the image forming unit 16 are provided. Each paper cassette 18, 19, 20,
Pickup rollers 83, 84, 8 for taking out the stored paper are provided in the bypass tray 21 and the bypass tray 22.
5, 86, 87, and a pair of paper feed rollers 88, 89, 90, 91, 92 for feeding the paper one by one to the transport path. A transport roller pair 93,
94, 95, and 96 are provided. The vertical transport path 81 and the bypass transport path 82 are joined on the right side of the secondary transfer upper roller 45 and the secondary transfer lower roller 67 of the transfer device 37, and a paper feed transport path 97 that supplies paper to the transfer device 37.
It is continuous. The paper feed path 97 is provided with a registration roller 98 for holding the paper conveyed from the paper feed unit 17 at a predetermined position. [Fixing Device] On the left side of the secondary transfer upper roller 45 and the secondary transfer lower roller 67 of the transfer device 37, a paper discharge transport path 99 for transporting the paper on which the toner image has been transferred is formed. Further, a fixing device 100 is disposed on the left side. The fixing device 100 includes a heating roller 101 having a built-in heater and a pressure roller 10 which is in pressure contact with the heating roller 101.
2 is provided for nipping and transporting the sheet between the two rollers, and heat-fixing the toner image formed on the sheet surface.

A sheet discharge roller pair 103 is provided on the left side of the fixing device 100, and is configured to discharge a sheet to a sheet discharge tray 104. [Control System] Inside the copying machine 1, a control unit 201 is provided as shown in FIG. The control unit 201 controls the CP
It is constituted by a microcomputer system including U, RAM, ROM, various drivers and the like. Control unit 201
Is connected to an operation panel 202 for performing various operation instructions. The operation panel 202 includes an input key unit including numeric keys and other command keys, a liquid crystal display element, and an LED.
And the like, and also includes a start key for instructing the start of a copying operation, a switch for setting a special paper mode, and the like.

The control unit 201 further includes an image reading unit 2
03 is connected. The image reading unit 203 includes the above-described optical system 23 and the like, irradiates a document placed on the document table 15 with light, and reflects light reflected from the document on the color image sensor 2.
In step 9, the image data is read and converted into an image data signal. The control unit 201 includes an image processing unit 20 that receives an image data signal output from the color image sensor 29 and performs image processing.
4 are connected. The image processing unit 204 restores a two-dimensional color image based on an image data signal output from the color imaging device 29,
The image is decomposed into images of magenta, yellow, and black color components.

An exposure unit 205 including the laser unit 40 is connected to the control unit 201. The exposure unit 205 irradiates a laser beam from the laser unit 40 based on the image information decomposed into each color component by the image processing unit 204, and forms an electrostatic latent image on the peripheral surface of the photosensitive drum 30.
Further, the control unit 201 is connected to a photosensitive drum driving unit 206 for driving the photosensitive drum 30 to rotate. The photoconductor drum driving unit 206 drives the photoconductor drum 30 to rotate in synchronization with the laser beam emitted from the exposure unit 205.

The control unit 201 includes a sheet transport system 20.
7 is connected. The paper transport system 207 includes a paper feed transport system including a drive motor 42 for rotationally driving the transfer belt 46, and a paper transport including a drive motor such as the paper discharge transport path 99, the fixing device 100, and a pair of paper discharge rollers 103. It is composed of systems. The paper transport system 207 can be set to at least one of a normal transport speed and a special paper transport speed that is lower than the normal transport speed, and performs speed control in accordance with the set mode. Is possible.

The control unit 201 includes a primary transfer upper roller 47.
And a primary transfer roller control unit 208 for moving the first transfer roller between the pressed position and the separated position. The primary transfer roller controller 208 presses and separates the primary transfer upper roller 47 from and to the photosensitive drum 30 by controlling the drive of the primary pressing cam drive motor 56.
In a normal operation, the upper primary transfer roller 47 and the lower primary transfer roller 48 transfer the transfer belt 46 to the photosensitive drum 30.
The primary transfer upper roller 47 is moved to the pressure contact position so as to be in pressure contact with the peripheral surface. In the special paper mode, the primary transfer upper roller 47 is moved so that the transfer belt 46 is separated from the photosensitive drum 30 peripheral surface. The upper transfer roller 47 is moved to the separated position.

The control unit 201 includes a secondary transfer lower roller 67.
Transfer roller control unit 2 for moving the sheet between a predetermined position at the time of transfer and a separated position separated from the transfer belt 46
09 is connected. This secondary transfer roller control unit 20
Numeral 9 is for controlling the motor for driving the secondary pressing cam to move the secondary transfer lower roller 67 toward and away from the transfer belt 46. Photoconductor drum 30
During the primary transfer of the toner image from the transfer belt 46 to the transfer belt 46, the secondary transfer lower roller 67 is separated from the transfer belt 46, and the second transfer of the toner image from the transfer belt 46 to the sheet is performed.
When performing the next transfer, the lower secondary transfer roller 67 is moved so that the gap between the peripheral surface of the lower secondary transfer roller 67 and the surface of the transfer belt 46 is a predetermined distance.

Further, a secondary transfer voltage control section 210 for controlling a voltage applied to the secondary transfer lower roller 67 is connected to the control section 201. Secondary transfer voltage controller 2
10 is a transfer belt 46 for attracting toner onto the paper from the back side of the paper and transferring the toner image to the front surface of the paper.
A voltage having a polarity opposite to that of the toner on the surface is applied to the lower secondary transfer roller 67. When the toner is negatively charged, the voltage applied to the secondary transfer lower roller is a DC bias voltage of about +1 kV to 2.5 kV. Immediately after the apparatus returns from the stop state, there is a possibility that toner has adhered to the secondary transfer lower roller 67, and the secondary transfer voltage controller 210 applies a predetermined voltage to the secondary transfer lower roller 67 for a certain period of time. Apply 2
The transfer belt 46 and the secondary transfer roller 67 are rotationally driven at a position where the next transfer lower roller 67 is close to the transfer belt 46. At this time, the voltage applied to the secondary transfer lower roller 67 has the same polarity as that during the transfer, and is a DC bias voltage of about +300 to 400V. However, when the cleaning blade 75 is not in contact with the secondary transfer lower roller 67, it is preferable that the voltage at this time be reverse polarity.

The control unit 201 is further connected to another input / output unit. [General Operation] The operation of the copying machine 1 will be described with reference to the flowchart shown in FIG. When the power of the copying machine 1 is turned on, various parameters and the entire apparatus are initialized in step S1 shown in FIG. During this initialization operation, a toner peeling voltage is applied to the lower secondary transfer roller 67 to transfer the transfer belt 46 and the lower secondary transfer roller 67.
Is rotated for a certain period of time, and the toner adhered to the secondary transfer lower roller 67 is retransferred to the transfer belt 46 and collected by the cleaning device 62 provided on the transfer belt 46. The toner peeling voltage applied to the secondary transfer lower roller 67 is determined by the cleaning blade 75
When it is in contact with seven circumferential surfaces, the DC voltage is +300 to 400V. Thereafter, the photosensitive drum 30, the transfer belt 46, and the like are set to the initial positions.

In step S2, it is determined whether or not the special paper mode has been set. Here, the operation panel 20
When the special paper mode is selected by the mode setting button 2, it is determined that the special paper mode has been set, and the process proceeds to step S 3. In step S3, an image forming process in the special paper mode is executed. If it is determined in step S2 that the special paper mode has not been set, the process proceeds to step S4. In step S4, the apparatus is set to the normal image forming mode. In step S5, it is determined whether or not an instruction to start image formation has been given. When a start key provided on the operation panel 202 is operated, it is determined that an instruction to start image formation has been given, and
Move to step S6.

In step S6, an image is formed on a sheet based on a normal image forming mode. Here, the original placed on the original table 15 is irradiated with light by the optical system 23, and the reflected light is converted into an image data signal by the color image sensor 29. The image data signal is decomposed into an image of each color component by the image processing unit 204, and first, an electrostatic latent image based on the cyan color component is formed on the photosensitive drum 30. This electrostatic latent image is visualized by the developing device 33 containing the cyan toner.

The upper primary transfer roller 47 is a photosensitive drum 3
It is located at a pressure contact position close to the 0 side, and the transfer belt 46 is pressed against the peripheral surface of the photosensitive drum 30 together with the primary transfer lower roller 48. As a result, the toner image formed of the cyan toner formed on the photosensitive drum 30 is transferred to the surface of the transfer belt 46 by the upper primary transfer roller 47 and the lower primary transfer roller 48.

When the toner image of the cyan toner is transferred to the transfer belt 46, an electrostatic latent image corresponding to magenta is formed on the photosensitive drum 30. The image is visualized. This toner image is similarly transferred onto the transfer belt 46. Hereinafter, similarly, the toner images of the respective color components of yellow and black are transferred onto the transfer belt 46 in a stacked state. When transferring toner images of each color component,
Synchronization is performed so that there is no image shift.
At the same time, the paper feed cassettes 18, 19, 20, 21,
The sheet is conveyed from any one of the bypass trays 22 and is made to stand by by the registration rollers 98 in the sheet feeding conveyance path 97.

When the transfer of the color toner image onto the transfer belt 46 is completed, the sheet is supplied from the registration roller 98 to between the upper secondary transfer roller 45 and the lower secondary transfer roller 67, and is stacked on the surface of the transfer belt 46. The color toner image formed in this state is transferred onto the sheet by the secondary transfer lower roller 67. Thereafter, the sheet having the color toner image transferred to the surface thereof is conveyed to the fixing device 100 through the sheet discharge conveyance path 99, and the color toner image transferred to the sheet surface is heated and melt-fixed and discharged to the sheet discharge tray 104. I do. During this time, 1
The next transfer upper roller 47 is located at the pressure contact position,
The surface of the transfer belt 46 is pressed against the peripheral surface of the photosensitive drum 30 by an upper primary transfer roller 47 and a lower primary transfer roller 48. The paper transport system 207 is set at a normal transport speed in synchronization with the photosensitive drum drive unit 206.

In step S7, it is determined whether a predetermined image forming operation has been completed. Here, the operation panel 20
When the copying operation of the number of sheets designated from Step 2 has been completed, it is determined that the predetermined image forming operation has been completed, and Step S8 is performed.
Move to In step S8, another process is executed. [Special Paper Mode] In the special paper mode in step S3, an operation as shown in FIG. 7 is executed. Step S11
Then, it is determined whether or not there is an instruction to start image formation.
Here, the paper feed cassettes 18, 19,
The user sets special paper for image formation on any of the bypass trays 20 and 21 and the bypass tray 22, and instructs from the operation panel 202 that paper is to be fed after the setting of the special paper. Special paper is cardboard, OHP sheet, surface coated paper with surface coating,
Usually, the setting is made in the bypass tray 22 in many cases. In this case, the setting to feed the paper from the bypass tray 22 may be instructed from the operation panel 202. Thereafter, when the start key provided on the operation panel 202 is operated, it is determined that there is an instruction to start image formation, and the process proceeds to step S12.

In step S12, a process of reading the document image placed on the document table 15 and transferring the color toner image onto the transfer belt 46 is executed. In this case, the original placed on the original platen 15 is irradiated with light by the optical system 23 and the reflected light is emitted by the color image sensor 29 in the same manner as in the case of forming an image on plain paper. Convert to a signal. The image data signal from the color image sensor 29 is decomposed into an image of each color component by the image processing unit 204, and an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 30 in the order of cyan, magenta, yellow, and black to form an image. The images are visualized by the developing devices 33, 34, 35, and 36, and are sequentially transferred to the transfer belt 46. At the same time,
7, the sheet is taken out from the position designated in advance, conveyed to the transfer device 37 side, and made to stand by by the registration roller 98.

At this time, the upper primary transfer roller 47 is located at a pressure contact position close to the photosensitive drum 30 side, and the paper transport system 207 operates in synchronism with the photosensitive drum drive unit 206 for normal operation. Each part is driven at the speed. In step S13, it is determined whether the primary transfer operation has been completed. Here, when the transfer of the cyan, magenta, yellow, and black toner images onto the transfer belt 46 is completed, it is determined that the primary transfer operation has been completed, and the process proceeds to step S14.

In step S14, the upper primary transfer roller 4
7 is moved to the separating position to separate the surface of the transfer belt 46 from the peripheral surface of the photosensitive drum 30, and the paper transport speed of the paper transport system 207 is set to a special paper transport speed lower than the transport speed in the normal operation. I do. The special paper transport speed is set to a speed at which the color toner image transferred in a laminated state on the surface of a material paper such as a thick paper, an OHP sheet, or a surface coated paper is sufficiently fused and fixed in the fixing device 100.

In step S15, the registration rollers 98
Is transported to the transfer device 37, and the secondary transfer operation for this paper is started. Here, the secondary transfer upper roller 45 is driven at the special paper transport speed, and the paper is transported at the special paper transport speed, and the color toner image formed on the transfer belt 46 is transferred onto the paper. . Thereafter, the sheet on which the color toner image has been transferred is conveyed to the fixing device 100, and the color toner on the sheet surface is fused and fixed, and
03, the sheet is discharged to the sheet discharge tray 104.

In step S16, it is determined whether a predetermined image forming operation has been completed. Here, operation panel 2
02, when the copying operation of the number of sheets specified from
It is determined that the predetermined image forming operation has been completed, and the process returns to the main routine. In this case, when an image is formed on a material paper such as a thick paper, an OHP sheet, or a surface-coated paper, the primary transfer upper roller 47 is set when the transfer of the toner image to the transfer belt 46 is completed. Is moved to the separating position to separate the surface of the transfer belt 46 from the peripheral surface of the photosensitive drum 30, and the paper is transported at a special paper transport speed lower than the normal transport speed of the paper transport system 207. Therefore, the color toner image transferred onto the sheet can be sufficiently fused and fixed, and the photosensitive drum 3
0 can be prevented from being rubbed against the transfer belt 46 and damaged. [Secondary Transfer Voltage Control] In the secondary transfer in which the toner image on the surface of the transfer belt 46 is transferred onto paper, the voltage applied to the secondary transfer lower roller 67 by the secondary transfer voltage control unit 210 is equal to the transfer belt. +1 kV of the opposite polarity to the toner on
It is set to 2.5 kV.

At the time of initial setting immediately after the power is turned on, a toner peeling voltage is applied to the lower secondary transfer roller 67 to transfer the transfer belt 46 and the lower secondary transfer roller 67 as described above.
Is rotated for a certain period of time to re-transfer the toner adhered to the secondary transfer lower roller 67 onto the transfer belt 46, and perform a roller initialization operation to collect the toner on the cleaning device 62 provided on the transfer belt 46. In this case, the cleaning blade 75 is provided in pressure contact with the secondary transfer lower roller 67, and the toner peeling voltage applied to the secondary transfer lower roller 67 by the secondary transfer voltage controller 210 is Is set to +300 to 400V of the opposite polarity.

When the paper jam or the apparatus cover is opened, the apparatus is stopped. FIG. 8 is a flowchart showing the operation at this time. In step S21, it is determined whether a paper jam has occurred. Here, it is provided at various locations such as a vertical transport path 81, a bypass transport path 82, a paper feed transport path 97, a paper discharge transport path 99, and a path from the fixing device 100 to the paper discharge roller pair 103 of the paper feed unit 17. It is determined based on the detection signal of the sheet detection sensor whether or not the sheet conveyance is normal. For example, if any of the paper detection sensors does not detect a paper after a predetermined time has elapsed, it is determined that a paper jam has occurred, and the process proceeds to step S23.

In step S22, it is determined whether or not the device cover is open. For example, a sensor that is turned off when the device cover is closed at a predetermined position and turned on when the device cover is open is provided, and based on a detection signal of this sensor, the device cover is opened and It is possible to determine whether or not there is. If the device cover is open, the process proceeds to step S23.

In step S23, the apparatus is stopped, the operation support input from the operation panel 202 is prohibited, and the paper jam occurrence position and the opened apparatus cover position are displayed on the liquid crystal display of the operation panel 202. Are displayed corresponding to the current state. In step S24,
It is determined whether or not the return operation has been completed. For example, when a paper jam has occurred, when the paper is removed from the location where the jam has occurred and the reset switch is operated, it is determined that the return operation has been completed. Further, when the apparatus cover is opened, when the sensor is turned off and the apparatus cover is closed, it is determined that the return work is completed. However, when removing paper from the location where a paper jam has occurred, it is necessary to open the device cover and perform the paper removal operation.If the device stops due to the paper jam, the device cover is closed. Is included in the return work. Therefore, the case where the apparatus cover is opened here means a case where the inside of the apparatus is operated due to toner supply, other maintenance, or the like, or a case where the apparatus cover is accidentally opened. In this step S24,
If it is determined that the return operation has been completed, the process proceeds to step S25.

In step S25, the same roller initialization work as that immediately after power-on is performed. Here, +30 having a polarity opposite to that of the toner on the surface of the transfer belt 46 is applied to the lower secondary transfer roller 67.
The transfer belt 46 and the secondary transfer lower roller 67 are driven to rotate for a predetermined time (here, 3 seconds) by applying a toner peeling voltage of 0 to 400 V. As a result, the toner adhered to the secondary transfer lower roller 67 is re-transferred to the transfer belt 46, and the cleaning device 6 provided on the transfer belt 46
Collect in 2.

For example, if the transfer of the toner image onto the transfer belt 46 is completed and a sheet jam occurs at the registration roller 98 when starting the secondary transfer, the sheet has not been conveyed to the transfer portion. Nevertheless, voltage application to the secondary transfer lower roller 67 is started, and the toner on the transfer belt 46 is transferred to the secondary transfer lower roller 67. Since the registration roller 98 and the transfer portion (the proximity position between the transfer belt 46 and the lower secondary transfer roller 67) are short, when the occurrence of paper jam is detected, the voltage application to the lower secondary transfer roller 67 has already started. Therefore, the toner is transferred to the lower secondary transfer roller 67. When the jammed sheet is removed and the apparatus returns from the stopped state, the secondary transfer lower roller 67
If the toner adhered to the sheet is left as it is, the toner adheres to the back side of the sheet at the time of the next image formation, and the sheet is soiled. Therefore, when the apparatus returns from the stop state, a predetermined toner peeling voltage is applied to the secondary transfer lower roller 67 to re-transfer to the transfer belt 46 side, and is collected by the cleaning device 62.

Further, even if the stop of the apparatus is not a paper jam at the registration roller 98, there is a possibility that toner has adhered to the secondary transfer lower roller 67, and when the apparatus returns from the stopped state, The lower transfer roller 6 for a predetermined time by always applying the toner peeling voltage as described above.
7 and the transfer belt 46 are driven to rotate.

The toner peeling voltage is set at the lower secondary transfer roller 67.
Is different depending on whether or not the cleaning blade 75 is pressed against the surface. In the above-described embodiment, since the cleaning blade 75 is pressed against the surface of the secondary transfer lower roller 67, it is preferable to apply a voltage having a polarity opposite to that of the toner on the surface of the transfer belt 46. 2
The toner is forcibly attached to the lower secondary transfer roller 67, and the voltage applied to the lower secondary transfer roller 67 is -200V, -150V.
V, -100V, -50V, 0V, + 50V, +100
V and +200 V, and the cleaning performance when the voltage application time was 3 seconds is shown in Table 1. From this, when the applied voltage is a negative voltage having the same polarity as the toner, the effect of removing the toner attached to the secondary transfer lower roller 67 is deteriorated. It was found that the effect of removing the toner adhered to the roller 67 was improved.

When there is no cleaning blade 75 in pressure contact with the peripheral surface of the secondary transfer lower roller 67, it is preferable to apply a voltage having the same polarity as that of the toner. When the cleaning blade 75 is not provided, the toner is forcibly attached to the lower secondary transfer roller 67, and the voltage applied to the lower secondary transfer roller 67 is -500V, -400V, -300V, -20.
0V, -150V, -100V, -50V, 0V, +5
0 V and +100 V, and the voltage application time is 3
The cleaning performance in seconds is shown in Table 1. From this, when the cleaning blade 75 is not provided, when the applied voltage is a negative voltage having the same polarity as the toner, the effect of removing the toner adhered to the secondary transfer lower roller 67 becomes good, and the applied voltage becomes the positive polarity having the opposite polarity to the toner. In the case of voltage,
It was found that the effect of removing the toner adhered to the secondary transfer lower roller 67 was deteriorated.

[0055]

[Table 1]

As described above, when the apparatus returns from the stop state, the toner adhering voltage is applied to the lower secondary transfer roller 67, and the adhered toner is retransferred to the lower secondary transfer roller 67 for cleaning. Therefore, it is possible to prevent the toner from adhering to the back surface of the paper and contaminating it. [Other Embodiments] (A) Modification of Special Paper Mode In the above-described embodiment, when the primary transfer operation on the transfer belt 46 is completed, the upper primary transfer roller 47 is moved to the separated position to transfer the transfer belt. 46 is separated from the photosensitive drum 30 and the paper transport system 207 is set to the special paper transport speed, but the secondary transfer operation is started at a normal transport speed,
When the leading end of the sheet reaches the fixing device 100, the upper primary transfer roller 47 is moved to the separation position to separate the transfer belt 46 from the photosensitive drum 30, and the sheet conveyance system 207 is driven at a special sheet conveyance speed. It can also be configured as follows.

FIG. 9 shows a flowchart in this case.
In step S31, it is determined whether an instruction to start image formation has been given. Here, similarly to the above-described embodiment, when the start key provided on the operation panel 202 is operated, it is determined that there is an instruction to start image formation, and the process proceeds to step S32.

In step S32, a process of reading the document image placed on the document table 15 and transferring the color toner image onto the transfer belt 46 is executed. Here, similarly to the above-described embodiment, a toner image is formed on the photosensitive drum 30 for each color component and is sequentially transferred to the transfer belt 46, and the color toner image in which the toner images of the respective color components are stacked is transferred to the transfer belt 46. Form on top. At the same time,
The sheet is taken out from the position designated in advance among them, conveyed to the transfer device 37 side, and made to stand by by the registration roller 98. At this stage, the upper primary transfer roller 47 is located at the pressure contact position close to the photosensitive drum 30 side,
The paper transport system 207 drives each unit at a normal operation speed in synchronization with the photosensitive drum driving unit 206.

In step S33, transfer of the toner image by the last color component to the transfer belt 46 is started.
It is determined whether or not the reference position of the transfer belt 46 has reached a predetermined position. At the side edge of the transfer belt 46, detection holes are provided at regular intervals in the rotation direction, and a sensor such as a photo interrupter that detects the detection holes and generates a timing signal is provided. For the alignment of each toner image at the time of the primary transfer and the alignment of the color toner image and the paper at the time of the secondary transfer, a reference position is set in accordance with the position of the detection hole of the transfer belt 46. Is performed by synchronizing the respective units with the timing of the position. Therefore, here, a reference position is set corresponding to the position where the transfer of the toner image is started on the transfer belt 46, and when the reference position becomes the predetermined position, the color image on which the toner images of the respective color components are stacked is set. It is determined that the front end of the toner image has reached near the nip position between the upper secondary transfer roller 45 and the lower secondary transfer roller 67, and the process proceeds to step S34.

In step S34, the registration rollers 98
Is transported to the transfer device 37, and the secondary transfer operation for this paper is started. Here, the transport speed of the paper transport system 207 is set to a normal transport speed. In step S35, it is determined whether or not the leading edge of the sheet has reached the vicinity of the fixing device 100. Here, when a sheet is detected by a sheet detection sensor (not shown) disposed immediately before the fixing device 100 in the sheet discharge conveyance path 99, it is assumed that the sheet has reached the vicinity of the fixing device 100.
Move to step S36.

In step S36, the upper primary transfer roller 4
7 is moved to the separating position to separate the surface of the transfer belt 46 from the peripheral surface of the photosensitive drum 30, and the paper transport speed of the paper transport system 207 is set to a special paper transport speed lower than the transport speed in the normal operation. I do. At this time, the transfer of the color toner image from the transfer belt 46 onto the sheet continues. When the paper reaches the fixing device 100, one of the toner images from the photosensitive drum 30 to the transfer belt 46 is transferred.
Since it is considered that the next transfer has been completed, no problem occurs even if the transfer belt 46 is separated from the peripheral surface of the photosensitive drum 30.

The sheet having reached the fixing device 100 is conveyed at a special sheet conveying speed, and the color toner transferred to the sheet surface is melted and fixed on the sheet by the heating roller 101. In the step S37, it is determined whether or not the predetermined image forming operation has been completed. Here, when the number of copies specified by the operation panel 202 has been completed, it is determined that the predetermined image forming operation has been completed, and the process returns to the main routine.

According to the embodiment of the present invention, it is possible to form an image on a sheet in accordance with the length of the transfer belt 46 in the rotation direction, and to perform primary image formation from the peripheral surface of the photosensitive drum 30 to the transfer belt 46. Even if the transfer position and the secondary transfer position from the transfer belt 46 to the paper are close, the secondary transfer operation can be started before the primary transfer operation is completed, and the processing speed can be increased. In addition, the degree of freedom in device design can be increased.

[0064]

According to the image forming apparatus of the present invention, even when a color image is formed on material paper such as thick paper, OHP paper, surface-coated paper, etc., sufficient heat is applied to the fusion and fixing of the toner. And appropriate image formation is enabled.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a copying machine employing an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part thereof.

FIG. 3 is an enlarged view of a main part thereof.

FIG. 4 is an enlarged view of a main part thereof.

FIG. 5 is a control block diagram thereof.

FIG. 6 is a control flowchart thereof.

FIG. 7 is a control flowchart thereof.

FIG. 8 is a control flowchart thereof.

FIG. 9 is a control flowchart of another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copier 10 Main body 15 Document table 16 Image forming part 17 Paper supply part 22 Bypass tray 23 Optical system 30 Photoconductor drum 33 Developing device 34 Developing device 35 Developing device 36 Developing device 37 Transfer device 39 Exposure device 45 Secondary transfer upper roller 46 Transfer Belt 47 Primary Transfer Upper Roller 48 Primary Transfer Lower Roller 67 Secondary Transfer Lower Roller 97 Feeding Conveying Path 99 Discharging Conveying Path 100 Fixing Device 101 Heating Roller 102 Pressure Roller 201 Control Unit 202 Operation Panel 203 Image Reading Unit 204 image processing unit 205 exposure unit 206 photosensitive drum drive unit 207 paper transport system 208 primary transfer roller control unit 209 secondary transfer roller control unit

Claims (8)

[Claims] A photosensitive drum, an exposure unit for forming an electrostatic latent image on the peripheral surface of the photosensitive drum according to a color component of an image to be formed, and an electrostatic latent image formed on the peripheral surface of the photosensitive drum. Developing means for developing an image into a toner image with a corresponding color toner, an intermediate transfer member on which a color toner image formed by transferring the toner image formed on the surface of the photoconductor drum and being laminated is formed, The intermediate transfer member is movable between a position where the intermediate transfer member is pressed against the photosensitive drum peripheral surface and a position where the intermediate transfer member is separated from the photosensitive drum peripheral surface, and is formed on the photosensitive drum peripheral surface. A primary transfer means for transferring the transferred toner image to the surface of the intermediate transfer member, and a color formed on the intermediate transfer member on a sheet pressed against the intermediate transfer member and conveyed between the intermediate transfer member. Secondary to transfer toner image Transfer means, a heating roller having a built-in heater, and a pressure roller for pressing against the heating roller, while nipping and conveying the sheet on which the color toner image has been transferred, and heat fixing the color toner image A special paper setting unit for setting each unit to a special paper mode for forming an image on a special paper; and when the special paper mode is set by the special paper mode setting unit, at least an intermediate position of the primary transfer unit. When the transfer of the color toner image to the transfer member is completed, the primary transfer device is moved so that the intermediate transfer member is separated from the peripheral surface of the photosensitive drum, and the fixing device, the secondary transfer device, A special paper transfer control means for driving the intermediate transfer body at a special paper transport speed lower than a normal transport speed. 2. The image forming apparatus according to claim 1, wherein said intermediate transfer member is a transfer belt stretched between a driving roller and a driven roller. 3. The image forming apparatus according to claim 1, wherein the primary transfer unit is disposed on an inner peripheral surface side of the transfer belt, and a pressing position for pressing the transfer belt against the peripheral surface of the photosensitive drum; 1 that can be moved between the separated position to be separated
The image forming apparatus according to claim 2, wherein the image forming apparatus is a secondary transfer roller. 4. The primary transfer means includes a primary transfer upper roller and a primary transfer lower roller. When the special paper mode is set by the special paper setting means, the primary transfer upper roller and the primary transfer upper roller are connected to each other. The image forming apparatus according to claim 3, wherein at least one of the rollers to which the next transfer is performed is moved to the separated position. 5. The image forming apparatus according to claim 1, wherein said developing means includes a plurality of developing devices corresponding to each color component. 6. The image forming apparatus according to claim 5, wherein said developing device includes four developing devices corresponding to respective color components of cyan, magenta, yellow, and black. 7. A special paper mode according to claim 1, wherein said special paper setting means includes a mode setting receiving means, and sets each unit to a special paper mode when an operator operates said mode setting receiving means. An image forming apparatus according to any one of the above. 8. The special paper setting means includes a determination means for determining whether or not the paper conveyed between the intermediate transfer member and the secondary transfer means is a special paper. 7. The image forming apparatus according to claim 1, wherein each of the units is set to a special paper mode when it is determined that the paper is special paper.