JP2001194923A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact image forming device that is capable of suppressing the defective separation of a recording sheet and the jamming of the sheet at a secondary transfer part. SOLUTION: The image forming device 10 is provided with photoreceptors 42Y, 42M, 42C and 42K for forming toner images on respective surfaces, an intermediate transfer belt 38 to which the toner images formed on the photoreceptors 42Y, 42M, 42C and 42K are primarily transferred, a secondary transfer roller 54 which is brought into press contact with the intermediate transfer belt 38, and secondarily transfer the toner images transferred on to the intermediate transfer belt 38 to the recording sheet which passes through a press contact part between the intermediate transfer belt 38 and the roller 54, and a control part 84 for controlling the secondary transfer roller 54 so that the press contact force of the roller 54 may be reduced based on an image forming condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copier, a printer, and the like, which secondarily transfer a developer image primary-transferred from an image carrier to an intermediate transfer member to a recording sheet using a contact type secondary transfer means.
The present invention relates to an image forming apparatus such as a facsimile machine or a multifunction peripheral thereof.

[0002]

2. Description of the Related Art Conventionally, in Japanese Patent Application Laid-Open No. 10-228180, in a secondary transfer portion where a toner image is secondarily transferred from an intermediate transfer member to a recording sheet, a pressing force of a secondary transfer roll against a leading end of the recording sheet is used. There is disclosed an image forming apparatus that performs control for increasing the image quality. Also, Japanese Patent Application Laid-Open No. Hei 9-19008
In Japanese Patent Application Laid-Open No. 9-209, a pressing member that presses a recording sheet against a photoreceptor via a belt is provided at a transfer portion where a toner image is transferred from a photoreceptor to a recording sheet conveyed by a belt. There is disclosed an image forming apparatus that performs control to reduce the pressing force of a pressing member when an end portion passes through a transfer unit.

[0003]

However, in the image forming apparatus disclosed in the former publication, when the pressure of the secondary transfer roll is increased when the recording sheet is thin paper or the like, the recording sheet adheres to the intermediate transfer member. As a result, there is a problem that poor separation of the recording sheet and jam easily occur. Further, the image forming apparatus disclosed in the latter publication has a problem that the provision of a special pressing member leads to an increase in the size of the apparatus.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact image forming apparatus with less occurrence of recording sheet separation failure and jam in a secondary transfer section.

[0005]

To achieve the above object, an image forming apparatus according to the present invention comprises an image carrier having a surface on which a developer image is formed, and a developer image formed on the image carrier. The secondary transfer of the developer image transferred onto the intermediate transfer body to a recording sheet that is pressed against the intermediate transfer body to be primarily transferred and passes through a pressure contact portion between the intermediate transfer body and the intermediate transfer body The image forming apparatus includes a secondary transfer unit and a control unit that performs control to weaken the pressing force of the secondary transfer unit based on image forming conditions.

In the image forming apparatus of the present invention, the image forming condition may be a type of a recording sheet.

In the image forming apparatus of the present invention, the image forming condition may be image information for a developer image formed on the image carrier. In this case, the image information may be an area or an area ratio of the image, or may be an area or an area ratio of the image at the leading end of the image.

Further, in the image forming apparatus of the present invention, the pressing force of the secondary transfer means may be weakened with respect to the leading end of the recording sheet in the conveying direction, or may be reduced with respect to the trailing end of the recording sheet in the conveying direction. Alternatively, the pressing force of the secondary transfer means may be reduced.

Furthermore, in the image forming apparatus of the present invention,
The pressing force may be weakened by changing the position of the secondary transfer unit.

[0010]

According to the image forming apparatus of the present invention, control is performed such that the pressing force of the secondary transfer means against the recording sheet passing through the pressure contact portion between the intermediate transfer member and the secondary transfer means is reduced based on the image forming conditions. Therefore, for example, especially when the recording sheet is a thin paper with weak stiffness, it is possible to reduce the adhesion of the recording sheet to the intermediate transfer body, and to suppress the occurrence of poor separation of the recording sheet and jam. . Further, in the image forming apparatus of the present invention, since a special pressing member for changing the pressing force of the recording sheet against the intermediate transfer body is not provided, the apparatus can be made compact without increasing the size.

Further, in the image forming apparatus of the present invention wherein the pressing force of the secondary transfer means against the leading end or the leading end and the trailing end in the conveying direction of the recording sheet is reduced, Of the recording sheet from the intermediate transfer member can be improved.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an overall configuration of a digital full-color copying machine (hereinafter, simply referred to as a "copying machine") 10 according to an embodiment of the present invention. Copier 10
Is composed of an image reader section 20 for reading a document image, and a printer section 30 for reproducing the document image read by the image reader section 20.

The image reader unit 20 includes a document table 22 on which a document is placed, a scanner 24 for exposing and scanning the document placed on the document table 22 while moving the document in the direction of arrow a, and reflection by exposure by the scanner 24. Light is incident through an optical system including a plurality of mirrors and lenses, and a CCD that photoelectrically converts the reflected light into multi-valued electrical signals of R, G, and B for each pixel.
It has a sensor 26 and an image signal processing unit 28 to which the multi-valued electric signal is inputted as analog data of reflectance.

At an approximate center of the printer section 30, there is disposed an endless intermediate transfer belt 38 which is wound around three rollers 32, 34, 36 and is driven to rotate in the direction of arrow b. In the lower part of the intermediate transfer belt 38, four image forming units corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively, in order along the moving direction (the direction of arrow b). 40Y, 40M, 40C, 40
K is arranged. The intermediate transfer member is not limited to a belt-shaped one, and may be another shape such as a drum or a roller.

Each of the image forming units 40Y, 40M, 40C,
40K is a cylindrical photoconductor 4 that is driven to rotate in the direction of the arrow.
2Y, 42M, 42C and 42K, respectively.
Around each photoconductor 42Y, 42M, 42C, 42K,
The photoconductors 42Y, 42M, and 4 are sequentially arranged along the rotation direction.
Charger 4 for uniformly charging the surface of 2C, 42K
4Y, 44M, 44C, and 44K and fixed scanning type exposure devices 46Y, 46M, which expose the surfaces of the uniformly charged photoconductors 42Y, 42M, 42C, and 42K to form an electrostatic latent image.
46C, 46K, and photoconductors 42Y, 42M, 42C, 4
A magnetic brush type developing device 48 which develops each electrostatic latent image formed on 2K with a yellow toner, a magenta toner, a cyan toner, and a black toner to form a toner image.
Y, 48M, 48C, and 48K, and the respective photoconductors 42Y, 42M, 42C, and 42K via the intermediate transfer belt 38. The respective color toner images formed on the photoconductors 42Y, 42M, 42C, and 42K are intermediately formed. Transfer rollers 50Y, 50M, 50C, 5 for primary transfer onto the transfer belt 38, respectively
0K, and the photoconductors 42Y, 42M, 42C,
Cleaning devices 52Y, 52M, 52C and 52K for collecting the toner remaining on 42K are arranged respectively.

A secondary transfer roller 54 is disposed so as to sandwich the intermediate transfer belt 38 between the intermediate transfer belt 38 and one roller 32 that supports the intermediate transfer belt 38. Secondary transfer roller 5
4, at least the outer peripheral portion is made of a conductive elastic material,
At the time of the secondary transfer, a voltage having a polarity opposite to that of the toner is applied by a power supply (not shown).

The secondary transfer roller 54 is connected to the intermediate transfer belt 3
8 can be adjusted. As the adjusting mechanism, for example, as shown in FIG. 2, an elliptical cam 58 attached to a rotating shaft 56 of the secondary transfer roller 54 is used.
And an elastic member 6 made of rubber, spring, or the like, one end of which is fixed.
0 is in contact with the other end. In this adjustment mechanism, in the normal state shown in FIG. 2A, the secondary transfer roller 54 is strongly pressed against the intermediate transfer belt 38 by the urging force of the elastic member 60, but as shown in FIG. 2B. When the cam 54 is rotated, the urging force of the elastic member 60 is weakened.
The pressing force of No. 4 decreases.

The mechanism for adjusting the pressing force of the secondary transfer roller 54 against the intermediate transfer belt 38 is not limited to that shown in FIG. 2, and various mechanisms can be employed. For example, as shown in FIG.
The pressing force of the secondary transfer roller 54 may be adjusted by changing the urging force of the elastic member 60 by moving the lever 66 forward and backward. In this case, FIG. 3A shows a normal state where the pressing force of the secondary transfer roller 54 is strong, and FIG. 3B shows a state where the pressing force of the secondary transfer roller 54 is weakened. By using such an adjusting mechanism, the pressing force of the secondary transfer belt 54 can be finely controlled stepwise by finely controlling the rotation of the gear 62.

As another adjusting mechanism, as shown in FIG. 4, the pressing force of the secondary transfer roller 54 is adjusted by changing the position of the secondary transfer roller 54 with respect to the roller 32 supporting the intermediate transfer belt 38. You may. in this case,
FIG. 4A shows a normal state in which the secondary transfer roller 54 is at the normal position, and FIG. 4B shows that the pressing force is reduced by lowering (or raising) the position of the secondary transfer roller 54 from the normal position. It shows the state that it was turned on.

Referring again to FIG. 1, a paper feed unit 70 is disposed below the printer unit 30. The size of a recording sheet (not shown) loaded in the paper feeding unit 70 is detected by the sensor 72, and the type thereof is detected by the sensor 74.

The recording sheet sent out from the paper supply unit 70 by the paper supply roller 76 is a timing roller pair 78.
Through the nip portion, the pressure contact portion of the secondary transfer roller 54, and the fixing device 80.

The printer unit 30 is also provided with a control unit 84. The control unit 84 performs control to weaken the pressing force of the secondary transfer roller 54 based on image forming conditions as described later.

Next, the operation of the copying machine 10 having the above configuration will be described. Platen 2 of image reader unit 20
When a document is placed on the scanner 2 and a start button on an operation panel (not shown) is pressed, the scanner 24 performs exposure scanning while moving in the direction of arrow a to read a document image. The read document image is photoelectrically converted by the CCD sensor 26 into R, G, B three-color multi-valued electric signals, and these multi-valued electric signals are input to the image signal processing unit 28 as reflectance analog data. You. After performing various processes on the input data, the image signal processing unit 28 outputs image data of each color of yellow, magenta, cyan, and black to an exposure device driver (not shown). The exposure device driver controls each of the image forming units 40Y, 40M, 4 based on the input image data.
0C, 40K exposure apparatuses 46Y, 46M, 46C, 46
K are respectively driven.

In the image forming unit 40Y, an electrostatic latent image is formed on the surface of the photoreceptor 42Y, which is uniformly charged by the charging charger 44Y and rotates in the direction of the arrow, by exposure from an exposing device 46Y, and this electrostatic latent image is developed. The toner is developed by being rubbed with a magnetic brush of a two-component developer composed of a yellow toner and a carrier by the device 48Y to form a yellow toner image. This yellow toner image is formed on the intermediate transfer belt 38 by the action of the primary transfer roller 50Y. The primary transfer is performed by electrostatic attraction.

In the image forming unit 40M, an electrostatic latent image is formed on the surface of the photosensitive member 42M, which is uniformly charged by the charging charger 44M and rotates in the direction of the arrow, by exposure from the exposure device 46M, and this electrostatic latent image is developed. The magenta toner image is developed by being rubbed with a magnetic brush of a two-component developer composed of magenta toner and carrier by the device 48M, and the magenta toner image is formed on the intermediate transfer belt 38 by the action of the primary transfer roller 50M. It is electrostatically attracted and primary-transferred onto the yellow toner image.

In the image forming unit 40C, an electrostatic latent image is formed on the surface of the photoreceptor 42C, which is uniformly charged by the charging charger 44C and rotates in the direction of the arrow, by exposure from the exposure device 46C, and this electrostatic latent image is developed. The toner is developed by being rubbed with a magnetic brush of a two-component developer composed of a cyan toner and a carrier by the device 48C to form a cyan toner image.
By the action of C, the toner is electrostatically attracted onto the intermediate transfer belt 38 and primary-transferred onto each of the yellow and magenta toner images.

In the image forming unit 40K, an electrostatic latent image is formed on the surface of the photoreceptor 42K, which is uniformly charged by the charging charger 44K and rotates in the direction of the arrow, by exposure from the exposing device 46K, and this electrostatic latent image is developed. The toner is developed by being rubbed with a magnetic brush of a two-component developer composed of a black toner and a carrier by the device 48K to become a black toner image, and this black toner image is formed on the intermediate transfer belt 38 by the action of the primary transfer roller 50K. The toner is electrostatically attracted and primary-transferred onto the yellow, magenta, and cyan toner images.

The four color toner images thus superimposed on the intermediate transfer belt 38 move to the pressure contact portion of the secondary transfer roller 54 as the intermediate transfer belt 38 rotates. In synchronization with this, the sheet feeding roller 70
The recording sheet sent out by 6 is sent to the press-contact portion of the secondary transfer roller 54 at a timing by the timing roller pair 78. At this time, the control unit 84 performs the following control.

This processing is read out from a main routine (not shown), and as shown in FIG. 5, the control section 84 receives the output result of the light reflection type sensor 74 provided in the paper feeding unit 70 (step S1). It is determined whether or not the fed recording sheet is plain paper (step S2). If it is determined that the paper is plain paper (YES in step S2), it is determined whether the paper is thin paper (step S3). If it is determined that the paper is thin (YES in step S3), the pressing force A is selected as the pressing force of the secondary transfer roller 54 (step S4), and the pressing force of the secondary transfer roller 54 is changed from the normal pressing force B. The pressing force is changed to A (step S5). The pressing force A is smaller than the pressing force B, so that the pressing force of the secondary transfer roller 54 is reduced. On the other hand, if it is determined that the recording sheet is not plain paper (NO in step S2), or it is determined that the recording sheet is not thin even if it is plain paper (N in step S3).
O), the pressing force B is selected as the pressing force of the secondary transfer roller 54 (step S6), and the pressing force of the secondary transfer roller 54 is maintained at the normal pressing force B. After ending this processing, the process returns to the main routine.

At the pressure contact portion of the secondary transfer roller 54, the toner images of the respective colors on the intermediate transfer belt 38 are electrostatically attracted by the action of the voltage applied to the secondary transfer roller 54, and are collectively subjected to the secondary transfer on the recording sheet. Transcribed. At this time, FIG.
As shown in (b), when the secondary transfer roller 54 is in a normal pressure contact state, the roller 32 bites into the secondary transfer roller 54 made of an elastic material via the intermediate transfer belt 38, and the intermediate transfer belt 38 A press contact portion P2 with which the secondary transfer roller 54 makes wide surface contact is formed. When the recording sheet S passes through the pressure contact portion P2, the leading end of the recording sheet S is curved along the intermediate transfer belt. High in nature.

On the other hand, when the recording sheet is thin paper as described above, the pressing force of the secondary transfer roller 54 is set to be weak. Thereby, as shown in FIG.
Between the intermediate transfer belt 38 and the secondary transfer roller 54, a pressure contact portion P1 having a small contact area and a substantially linear contact state is formed. The thin paper passing through the press contact portion P1 can pass in a substantially straight state. As a result, it is possible to reduce the adhesion of the leading end of the thin paper in the conveyance direction to the intermediate transfer belt 38, and it is possible to suppress the occurrence of poor separation of the recording sheet and the occurrence of jam.

The recording sheet on which the toner image has been secondarily transferred is discharged onto a discharge tray 82 after the toner image is fixed by the fixing device 80.

As described above, in the copying machine 10 according to the present embodiment, when the recording sheet is thin paper, control is performed in the secondary transfer section to reduce the pressing force of the secondary transfer roller 54 against the recording sheet. Therefore, it is possible to suppress the occurrence of poor separation and jam due to the recording sheet being in close contact with the intermediate transfer belt 38. Further, in this embodiment, since no special pressing member for changing the pressing force of the recording sheet against the intermediate transfer belt 38 is provided, the apparatus can be made compact without increasing the size.

Next, various modifications of the control in the control section 84 will be described. According to these modified examples, the same effects as described above can be obtained.

In the above-described example, whether or not the recording sheet is thin paper is determined by the sensor, but as shown in FIG.
In response to a key input process performed by the user on the operation panel (step S8), it may be determined whether the recording sheet is thin paper. Subsequent processing is the same as steps S2 to S6 in FIG. When this process ends, the process may return to the main routine.

In the example shown in FIG.
(In the case of a printer, image data input from an external device such as a personal computer) by the controller 84
In this case, the area or the area ratio X of the entire image is calculated (step S9). Then, a reference area or area ratio Y previously stored in the memory is called (step S10), and is compared with the calculation result X (step S11). If the calculation result X is larger than the reference value Y, the secondary transfer roller 5
4 is performed to reduce the pressing force (steps S4 and S4).
5) If the calculation result X is equal to or less than the reference value Y, the secondary transfer roller 54 is maintained at the normal pressing force (step S).
6). After ending this processing, the process returns to the main routine.

In the example shown in FIG.
Is stored in the memory within the control unit 84, and at this time, the area or the area ratio X of the image front end is calculated (step S12). Then, the reference area or area ratio Y stored in the memory in advance is called (step S13) and compared with the calculation result X (step S14). If the calculation result X is larger than the reference value Y, the secondary transfer roller 5
4 is performed to reduce the pressing force (steps S4 and S4).
5) If the calculation result X is equal to or less than the reference value Y, the secondary transfer roller 54 is maintained at the normal pressing force (step S).
6). After ending this processing, the process returns to the main routine.

In the example shown in FIGS. 10 to 12, first, when the leading end portion in the transport direction of the recording sheet S is detected by the leading / rear end detecting sensor 86 disposed below the secondary transfer roller 54, FIG.
As shown by 0, the pressing force of the secondary transfer roller 54 is reduced.
As a result, as shown in FIG. 11, the leading end of the recording sheet S passes through the pressure contact portion P1 having a small contact area and in a substantially linear contact state while maintaining a substantially straight shape. Then, as shown in FIG. 12, after a lapse of a predetermined time from the detection of the leading end of the recording sheet S by the leading and trailing edge detection sensor 86, the secondary transfer roller 54 is returned to the normal pressing force. In this case, the recording sheet S may be passed to the end while the secondary transfer roller 54 is in the state of the normal pressing force. However, as shown in FIG.
When the rear end portion in the conveyance direction is detected, control may be performed to reduce the pressing force of the secondary transfer roller 54 again. As a result, the rear end of the recording sheet S passes through the press-contact portion P1 having a low press-contact force. As described above, by weakening the pressing force of the secondary transfer roller 54 against the leading end or the leading end and the trailing end in the transport direction of the recording sheet S, the end of the recording sheet S with respect to the intermediate transfer belt 38 can be statically moved. The electroadhesive force can be reduced, and as a result, the intermediate transfer belt 3
8 improves the separation performance of the recording sheet S. Also, by reducing the pressing force of the secondary transfer roller 54 against the trailing edge of the recording sheet S, the jumping of the trailing edge of the recording sheet is reduced. Less.

In the copying machine 10 described above, the roller 54 is used as the secondary transfer means. However, the secondary transfer means has another shape, for example, as shown in FIGS. 14 (a) and 14 (b). The rotating brush 54a or the fixed brush 54b may be used,
A blade 54c or a film 54d as shown in FIGS. 14C and 14D may be used.

Further, in the above description, a so-called tandem type copying machine in which a plurality of image forming units corresponding to respective colors have respective photoconductors has been described as an example. However, the present invention is not limited to a tandem type image forming apparatus. For example, FIG.
As shown in FIG. 7, for example, four developing devices 48Y, 48M, and 48 held by one photoreceptor 42 and a rotary rack 92.
C, 48K, and each developing device 48Y, 48M, 48
The present invention can also be applied to an image forming apparatus 90 of a type in which each color toner image formed on the photoreceptor 42 by C and 48K is primary-transferred sequentially to the intermediate transfer belt 38. here,
The same components as those of the copying machine 10 are denoted by the same reference numerals,
The redundant description of the secondary transfer roller 54, the sensor 74, the control unit 84, and the like will be omitted.

Further, the present invention is not limited to an electrophotographic image forming apparatus, but can be applied to other types of image forming apparatuses, for example, an electrostatic recording type image forming apparatus.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a copying machine according to an embodiment of the present invention.

FIG. 2 is a side view showing a pressing force adjusting mechanism of a secondary transfer roller.

FIG. 3 is a side view showing another pressing force adjusting mechanism of the secondary transfer roller.

FIG. 4 is a diagram illustrating a state in which a position of a secondary transfer roller is changed to reduce a pressing force.

FIG. 5 is a control flowchart of a pressing force of a secondary transfer roller.

6A is a diagram illustrating a state in which the pressing force of the secondary transfer roller is weakened, and FIG. 6B is a diagram illustrating a state in which the secondary transfer roller is pressed with a normal pressing force.

FIG. 7 is a flowchart illustrating a modified example of the control of the pressing force of the secondary transfer roller.

FIG. 8 is a flowchart illustrating a modified example of the control of the pressing force of the secondary transfer roller.

FIG. 9 is a flowchart illustrating a modification of the control of the pressing force of the secondary transfer roller.

FIG. 10 is a diagram illustrating a state in which the leading end of the recording sheet is detected to reduce the pressing force of the secondary transfer roller.

FIG. 11 is a diagram illustrating a state in which the leading end of a recording sheet passes through a pressing portion of a secondary transfer roller in which a pressing force is weakened.

FIG. 12 is a diagram illustrating a state in which the pressing force of the secondary transfer roller is returned to a normal pressing force after the recording sheet has passed through the leading end.

FIG. 13 is a diagram illustrating a state in which a pressing force of a secondary transfer roller is reduced when a rear end portion of a recording sheet passes.

FIG. 14 is a view showing a modification of the secondary transfer means.

FIG. 15 is an overall configuration diagram of another image forming apparatus to which the present invention can be applied.

[Explanation of symbols]

10: copying machine (image forming apparatus), 38: intermediate transfer belt (intermediate transfer body), 42Y, 42M, 42C, 42K: photoconductor (image carrier), 54: secondary transfer roller (secondary transfer means) 84 a control unit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Shinichi Yoshimoto, Inventor Shinichi Yoshimoto 2-3-1-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside the Osaka International Building Minolta Co., Ltd. 2-3-13 Osaka International Building Minolta Co., Ltd. (72) Inventor Yoshinobu Hata 2-3-13 Azuchicho, Chuo-ku, Osaka City, Osaka Prefecture Osaka International Building Minolta Co., Ltd. F-term (reference) 2H027 DA09 DB01 DC02 ED24 EF09 2H032 AA05 BA07 BA11 CA02 CA15

Claims (8)

[Claims] An image carrier on which a developer image is formed, an intermediate transfer body on which a developer image formed on the image carrier is primarily transferred, and an intermediate transfer body that is pressed against the intermediate transfer body, Secondary transfer means for secondary-transferring the developer image transferred on the intermediate transfer body to a recording sheet passing through a pressure contact portion between the intermediate transfer body and a pressure contact of the secondary transfer means based on image forming conditions An image forming apparatus comprising: a control unit that performs control for weakening a force. 2. The image forming apparatus according to claim 1, wherein the image forming condition is a type of a recording sheet. 3. The image forming apparatus according to claim 1, wherein the image forming condition is image information for a developer image formed on the image carrier. 4. The image forming apparatus according to claim 3, wherein said image information is an area or an area ratio of an image. 5. The image information according to claim 3, wherein the image information is an area or an area ratio of an image at a front end of the image.
Image forming apparatus. 6. The image forming apparatus according to claim 1, wherein a pressing force of the secondary transfer unit is reduced with respect to a leading end of the recording sheet in a conveying direction. 7. The image forming apparatus according to claim 6, wherein the pressing force of said secondary transfer means is also weakened with respect to a rear end portion of said recording sheet in the conveying direction. 8. The image forming apparatus according to claim 1, wherein the pressing force is reduced by changing a position of the secondary transfer unit.