JP2000047498A - Transfer device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a satisfactory transfer in the transfer of a toner image formed on an image carrier (photoreceptor) to a sheet with the back surface of a sheet holding body (transfer belt) for holding and carrying the sheet to the transfer position being brought into contact with a transfer brush. SOLUTION: In order to transfer a toner image formed on a photoreceptor 23 to a sheet S, the sheet S is held by a transfer belt 13 and fed to a transfer position and the transfer is performed in the state where the sheet is brought into contact with the surface of a photoreceptor 23. Therefore a transfer means 26 consisting of a pressing member 33 for energizing a transfer brush to the photoreceptor 23 side to ensure a prescribed contact area L for bringing a transfer belt 13 into contact with the photoreceptor 23 through the sheet S and a transfer brush 34 making contact with the transfer belt 13 on the downstream side of an intermediate point P halving the contact area L is provided on the back surface side of the transfer belt 13 to constitute a transfer device. According to this, the sheet P starts to make contact with the photoreceptor 23 from the start point (a) of the contact area L and receives the transfer action by the transfer brush 34 after sufficiently attached to the photoreceptor 23, so that a satisfactory transfer can be preformed without disturbing the transfer of the toner image.

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 such as a copying machine and a laser beam printer using an electrophotographic system, and is used for transferring a toner image formed on an image carrier to a sheet. Further, the present invention relates to a transfer device which holds a sheet on a holding member, conveys the sheet to a transfer position, and applies a transfer potential to the back surface of the holding member, that is, the surface opposite to the surface holding the sheet, to perform transfer.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, an electrostatic latent image formed on a photosensitive member having a photosensitive layer, which is an image carrier, is visualized with a powder toner. The imaged toner image is transferred onto a sheet of paper, and since the toner has not been fixed, it is fused on the paper by fusing and pressing the toner by heat to fix it on the paper. Let me.

In order to transfer the toner image formed on the surface of the photoreceptor onto the sheet, the sheet is fed to a transfer position facing the photoreceptor, and the back surface of the sheet, that is, the side opposite to the surface facing the photoreceptor is transferred. A predetermined voltage is supplied to a corona discharger, a transfer roller and the like to charge the sheet itself and transfer the toner image. In this case, when a toner image of a single color is transferred onto the sheet, there is no particular problem such as misregistration of the toner image. Therefore, the sheet is directly guided to the above-described transfer position via a guide or the like and conveyed. Thus, the sheet is charged and transferred.

However, in recent years, colorization has progressed,
A method of forming a color image by superimposing and transferring monochromatic toner images of different colors on a sheet has been implemented. At this time, since the sheet is fed to the transfer position a plurality of times, an image defect due to color misregistration occurs unless the overlapping position is accurate.

[0005] Therefore, conventionally, the sheet is held by an electrostatic attraction action and conveyed to the above-described transfer position, thereby increasing the accuracy and eliminating color misregistration due to superposition. I have. For this reason, the sheet is temporarily suction-held by the holder, and is conveyed to the transfer position in that state. The back surface is charged to transfer the toner image.

When a corona charger is used as a means for performing the above-described transfer, the ozone generation rate is high, and this is not a good idea from the viewpoints of environment, power consumption, and the like. Therefore, recently, the back surface of the sheet holding member is brought into contact with a transfer roller or a transfer brush to transfer the toner image onto the sheet held on the surface of the holding member.

In a transfer device having a transfer roller or a transfer brush of this contact type, a conductive elastic roller or a conductive brush is brought into contact with a photoreceptor via the above-mentioned sheet holder to hold a toner image. The transfer is performed by applying a transfer potential to the sheet.

When a transfer roller is used as the transfer device, in order to increase the area (nip area) where the sheet and the photoreceptor come into contact with each other (longer in the transport direction), the transfer roller is constituted by an elastic rubber roller, You need to increase your power. Therefore, there is a problem of life due to elastic deformation of the transfer roller. In addition, since the transfer roller needs to be rotationally driven due to the pressure contact force, it is necessary to rotate the transfer roller in synchronization with the photoreceptor and the sheet holding member, so that the drive mechanism becomes complicated and the drive torque increases. Occurs.

On the other hand, when a transfer brush is used, the area in contact with the photosensitive member cannot be made large. To increase this, the transfer brush can be easily secured in a predetermined range by setting the transfer brush itself to be rigid and long in the transport direction. However, the back surface of the sheet holder is shaved with a hard brush, and the problem of the life of the sheet holder occurs. Further, it is conceivable that the transfer cannot be performed satisfactorily due to the problem of the contact state with the hard brush.

In order to secure a predetermined contact area between the photosensitive member and the sheet holding member via the sheet in a device using a transfer brush, for example, Japanese Patent Application Laid-Open No.
No. 9413 proposes a transfer device. In this method, a pressing member is provided on the upstream side of the transfer brush so that the sheet holding member is brought into contact with the photoreceptor, and the contact width (nip) is increased.

In order to transfer the toner image formed on the photoreceptor onto the sheet, a sheet holder for holding the sheet is provided, and the sheet held by the holder is pressed against the photoreceptor. In order to increase the transfer efficiency by transferring a toner image to a sheet by applying a transfer potential to a transfer brush provided in a contact state on the back side of the holding member in A transfer device is provided in which a pressing member for bringing the body into contact with the photoconductor is provided.

[0012]

As described above, according to the conventional transfer device, the transfer efficiency is improved by providing the transfer brush and providing the pressing member to increase the contact width between the sheet holding member and the photosensitive member. Is raised.

[0013] However, although the contact member is used to increase the contact width of the sheet holding member to the photoreceptor, it is taken into consideration that the transfer of the toner image to the sheet by the transfer brush is performed well. Absent. In other words, the transfer brush is simply brought into contact with the back surface of the sheet holding member which is pressed against the photosensitive member by the pressing member, and the transfer brush is brought into contact with the entire area of the contact area to transfer the toner. At present, good transfer cannot be expected even if it rises. In other words, the transfer of the toner image is started from the start point of the contact area, and it is considered that the toner is disturbed. This is not so problematic as to the transfer of a single color toner image, but in the case of a color image, it appears as a decrease in image quality due to color bleeding or the like.

According to the present invention, a toner image formed on a photosensitive member as an image bearing member is not disturbed on a sheet held by a sheet holding member using a transfer device, particularly a transfer brush, as described above. An object of the present invention is to provide a transfer device that enables transfer.

It is a further object of the present invention to provide a transfer apparatus which can achieve the above-mentioned objects and further increase the efficiency of toner image efficiency.

[0016]

According to a first aspect of the present invention, there is provided a transfer device for an image forming apparatus, comprising: a transfer unit configured to transfer a toner image formed on an image carrier onto a sheet; A sheet holding member that holds the sheet and conveys it to a transfer position in contact with the image carrier, and applies a transfer potential to a back side opposite to a surface holding the sheet with the sheet holding member, and applies the transfer potential to the held sheet. A transfer unit for transferring a toner image formed on the image carrier, wherein the transfer unit contacts a sheet holder to the image carrier via a sheet within a predetermined range. A pressing member that secures a contact area to be made, and a transfer brush that is in contact with the back surface of the sheet holder in the contact area on the downstream side in the moving direction of the sheet holding body of the pressing member. Above contact area Characterized by being arranged so as to contact with the downstream side of the 2 minutes the midpoint.

According to the transfer device having the structure described in the first aspect, the sheet is held by the sheet holding member, and is conveyed to a transfer position where the sheet is in contact with the image carrier. At the transfer position, the transfer unit presses the sheet holder toward the image carrier from the back surface of the sheet holder. Therefore, a pressing member is provided in the transfer unit, and an area (contact area) for contacting the sheet holder with the image carrier via the sheet is secured in a predetermined range at the transfer position. In this contact area, the transfer brush is brought into contact with the back surface of the sheet holding member to perform transfer. In this transfer, the transfer brush is provided so as to be in contact with the back surface of the sheet holding member on the downstream side of the midpoint which divides the contact area into two, so that the sheet is in contact with the image carrier carrying the toner image. After being in contact with and sufficiently familiarized with the toner, the toner is transferred by the transfer brush. Therefore, the toner image is satisfactorily transferred to the sheet, and good transfer can be achieved without disturbance of the toner image.

This will be described with reference to FIG.
The sheet holding member (13) is pressed toward the image carrier (23) by a pressing member (33) constituting the transfer means (26), and a predetermined contact area ( L). The other transfer brush (34) constituting the transfer means (26) is located on the back side of the sheet holder (13) on the downstream side with respect to the midpoint (P) where the brush divides the contact area (L) into two. It is provided so that it may contact.
Therefore, the sheet (C) is gradually brought into close contact with the image carrier (23) side from the start point (a) of the contact area (L), and is gradually moved to the middle point of the contact area (L) by the conveying action of the sheet holder. (P). The start point (a) is a point in time when the sheet and the image carrier start contacting, and it is considered that the portion between the two is unstable and a floating portion is formed. When the transfer operation is performed from the start point a, the toner image on the image carrier (23) side floats and starts to be transferred to the sheet S, and there is a concern that the toner image may be disturbed.

However, according to the first aspect of the present invention, the transfer brush (34) is such that the sheet (S) is an image carrier (23).
Since the transfer operation is performed after the middle point (P) of the contact area where the contact area is sufficiently contacted, the transfer of the toner image becomes possible without causing the transfer due to the disturbance of the toner image described above.

In FIG. 2, in the contact area (L), a gap between the sheet and the image carrier (23) may occur at the end point (b) where the sheet is separated from the image carrier (23). The toner image may be disturbed due to the transfer at that time. However, at this point, the transfer of the toner image is completed by the previous transfer operation, and there is almost no fear that the remaining toner flies by the transfer operation and disturbs the transferred toner image. Therefore, even when the transfer brush (34) is subjected to the transfer operation at the end point (b) in contact with the sheet holder (13), the toner image is not disturbed, and good transfer is possible.

According to a second aspect of the present invention, the transfer brush or the pressing member is provided with:
Alternatively, an urging means is provided so as to press the transfer brush and the pressing member against the back side of the sheet holding member, so that the transfer brush and the pressing member are urged and pressed. For example, by urging the transfer brush alone to the rear surface of the sheet holding body by the urging means, the transfer brush is fixed to the rear surface of the sheet holding body in a state where a predetermined contact area is secured by the pressing member. With such a pressure, good contact can be achieved, whereby stable transfer can be performed, and more efficient transfer can be expected. That is, the contact state can be adjusted favorably.

Further, by providing a single urging means for the pressing member and urging the sheet holding member toward the image carrier from the back surface, the contact area for bringing the sheet into contact with the image carrier can be easily reduced to an arbitrary amount. Can be set to That is, a favorable contact area can be set by the urging force of the urging means without being influenced by the transfer brush. In addition, the sheet can be pressed toward the image carrier regardless of the type of the sheet, for example, the thickness, the waist, the material, and the like, so that good transfer and transfer efficiency can be improved as described above. Become.

Further, if the transfer brush and the pressing member are provided on the same support, and the support is pressed and urged via the urging means, the transfer can be performed with a predetermined contact area secured. Bring the brush into good contact with the sheet holder,
Good transfer and transfer efficiency can be improved.

According to a third aspect of the transfer device having the above-described configuration, the transfer brush is transferred on the downstream side with respect to the center of the contact area in consideration of the deflection of the brush itself. It can be arranged to contact the belt. That is, when the transfer brush is pressed against the sheet holding member, the transfer brush is pressed against the sheet in a bent state, and good contact is possible. If the bending direction is set to be the moving direction of the sheet holding member, even if a part of the transfer brush is located on the upstream side of the midpoint of the contact area, the transfer brush and the sheet holding member are bent by the bending. The contact start position is on the downstream side with respect to the middle point. Therefore, there is a margin in designing the arrangement position of the transfer brush. In addition, the sheet holding member advantageously bends the transfer brush in the moving direction, and it can be expected that the above-mentioned points will be improved.

According to a fourth aspect of the present invention, there is provided a transfer device, wherein the transfer brush has a front end portion in contact with a sheet holder, and an upstream end in a moving direction of the sheet holder. If the transfer brush is formed so as to protrude from the downstream side, and when the leading end portion of the transfer brush comes into contact with the back surface of the sheet holder, the transfer brush concentrates and comes into contact with the back surface of the sheet holder. Therefore, since the transfer can be performed intensively, the transfer efficiency of the toner image is increased. In particular, when the transfer brushes are concentrated, the contact density of each brush with the sheet holder can be increased, and the transfer operation can be performed more favorably, thereby improving the transfer efficiency.

According to a fifth aspect of the present invention, there is provided a transfer device having the above-described configuration, wherein a pedestal attached to a support for pressing a transfer brush against the sheet holder is provided. If it is formed so as to be inclined to the downstream side in the moving direction, the same operation and effect as those of the fourth aspect can be obtained. further,
Since the leading end portion of the transfer brush can be formed in a flat state, its manufacture is simplified, and at the same time, the transfer brush is tilted in advance in the moving direction of the sheet holder, so that bending in that direction occurs, and a good sheet holder is obtained. Good contact is possible.

According to the transfer device having the above-described configuration, it is naturally more convenient to obtain a color image by successively overlapping toner images of different colors. In other words, when a toner image of the next color is further transferred onto the toner image transferred on the sheet, the toner image is transferred in a state where the previous toner image sufficiently overlaps with the next toner image and is familiar. Therefore, color blur etc. due to disturbance in the toner image is eliminated,
A color image with good image quality can be obtained.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings. In particular, FIG. 1 is a diagram showing a transfer position of a transfer brush constituting a transfer device according to an embodiment of the present invention, and FIG. 2 is a diagram showing transfer of a toner image of the transfer device shown in FIG. FIG. 4 is a diagram for explaining the principle of transfer. And FIG.
FIG. 4 is a side view for explaining the overall configuration of the transfer device, and FIG.
FIG. 7 to FIG. 7 are diagrams for illustrating a schematic configuration of the image forming apparatus and for explaining control, operation, and the like for image formation.

First, the configuration of an image forming apparatus provided with the transfer device of the present invention will be described with reference to FIG.

The image forming apparatus shown in FIG. 4 shows the configuration of a digital color copying machine. A transparent document table 2 on which a document is placed and an operation panel are provided on the upper part of the main body of the copying machine 1. The upper surface of the document table 2 is supported by the document table 2 so that it can be opened and closed. An automatic document feeder (ADF) 3 is mounted on the document table 2 with a predetermined positional relationship. Inside the digital copier 1 body,
A reading device 4 for reading an image of a document placed on the document table 2 and an image forming unit 10 are provided below the reading device 4.

The automatic document feeder 3 feeds the documents placed on the placing table 3a one by one to the document table 2, and when reading by the reading device 4 is completed, the document is discharged to the discharge tray 3b and at the same time the next document is discharged. The conveyance of the document is started, and the document is automatically sent to the document table 2. In the case of a document having images formed on both sides, the automatic document feeder 3 first conveys one side to the document table 2 and discharges the document when reading of that side is completed. Without reversing the front and back sides, the document is sent to the document table 2 again, and after reading the image on the opposite side of the document, the document is discharged and one side of the next document is fed to the document table 2. ing.

A reading device 4 for reading an image of a document sent to the document table 2 by the automatic document feeder 3 comprises:
A first scanning unit 5 and a second scanning unit 6 that are reciprocated in parallel with the document table 2 are provided. First
The scanning unit 5 supports an exposure lamp that illuminates the original, a mirror that reflects light reflected from the original to a target position, and the like. In addition, the second scanning unit 6 reflects the reflected light image reflected by the mirror to a CCD 8 as a reading element via an imaging lens 7 constituting the reading device 4.

The first scanning unit 5 runs at a predetermined scanning speed from a home position (left side in FIG. 3) when reading an image of a document. Then, the second scanning unit 6 travels in the same direction at half the scanning speed. As a result, the image of the document is sequentially formed on the CCD 8 via the image forming lens 7, and the CCD 8 outputs read data that has been photoelectrically converted. The CCD 8 is provided with R, G, and B CCDs for color-separating the image if the original is color, or a color separation filter or the like is arranged in the optical path to read the color-separated image. Output data. CC
The read data output from D8 is converted into image data by the image forming unit 1 through a processing circuit that performs image processing for forming a color image or the like in the image forming unit 10 as described later.
Transferred to 0.

The image forming section 10 for reproducing the image data obtained through the reading device 4 as a visible image on a sheet has a sheet feeding device 11 provided below. The sheet feeding device 11 is provided with a sheet feeding unit that stores the sheets S in a sheet feeding cassette or a tray and separates and feeds the sheets one by one. The sheet sent out by the sheet feeding device 11 includes a registration roller 1 disposed in front of an image forming position.
It is sent to 2. The registration roller 12 is a well-known one, and is configured to convey a sheet to an image forming position in a timely manner.

An image forming unit 10 is provided above the sheet feeding device 11.
A transport belt mechanism 14 for movably holding a transfer belt 13 as a sheet holding member constituting the image forming apparatus is provided. The transport belt mechanism 14 is provided with an endless transfer belt 13.
Are provided with a driving roller 15 and a driven roller 16 which stretch the belt. The transfer belt 13 is configured to electrostatically attract and transport the sheet P. Therefore, the driven roller 16 side is arranged corresponding to the registration roller 12 side,
A charging roller 17 is provided so as to be pressed against the driven roller 16 via the transfer belt 13.

A fixing device 18 for transferring a toner image transferred on a sheet S, which will be described later, to the sheet is disposed on the side of the drive roller 15 of the transport belt mechanism 14. As the sheet S passes between the fixing roller nips of the fixing device 18, the toner on the surface is melted and fused and fixed on the sheet surface. Further, the sheet S is transferred to the fixing device 1.
The sheet is conveyed while being fixed at 8, and is discharged by a discharge roller 20 via a transfer direction switching gate 19 to a discharge tray 21 provided so as to protrude outside the body of the copying machine 1.

The switching gate 19 selectively switches between discharging the fixed sheet to the discharge tray 21 as described above or re-supplying the sheet to the image forming position of the image forming section 10 again. The conveyance path of the sheet S is switched. If image formation on both sides of the sheet S is selected, the switching gate 19 is controlled so as to guide the sheet S to the switchback transport path 22. As a result, the sheet P is again conveyed to the registration roller 12 just before the image forming position in the image forming unit 10 after the sheet P is turned upside down via the switchback conveyance path 22.

On the other hand, the image forming unit 10 includes the above-described transport belt mechanism 14, particularly, a linear portion (horizontal portion) of the transfer belt 13.
First, second, third, and fourth image forming stations Pa, Pb, Pc, and Pd are arranged side by side in the order from the upstream side in the transport direction in the vicinity of the transfer belt 13. The transfer belt 13 is stretched between the driving roller 15 and the driven roller 16 as described above, and is frictionally driven in the arrow Z direction by the rotation of the driving roller 16. Then, the sheet conveyed via the registration roller 12 is held so as to be electrostatically attracted to the transfer belt 13 by the action of the charging roller 17. The sheet P is transferred to the image forming stations Pa,
It is sequentially transported to Pb, Pc, and Pd.

Each image forming station Pa, Pb, P
c and Pd have substantially the same configuration, and are a photosensitive member 23 which is a drum-shaped image carrier that is driven to rotate in the direction of arrow F in the figure.
a, 23b, 23c, and 23d. Chargers 24a, 24b, 24 for uniformly charging the photosensitive members are provided around the respective photosensitive members 23a, 23b, 23c, 23d.
c, 24d, and developing devices 25a, 25b, 25 for visualizing the electrostatic latent image formed on the photoreceptor with toner of each color.
c, 25d, and transfer means 26a, 26b, 2 which are provided in contact with the back surface of the transfer belt 13 to transfer the developed toner image to a sheet, and which constitute the transfer device of the present invention.
6c and 26d, and cleaning devices 27a, 27b, 27c and 27c for removing toner remaining on the photoreceptor surface after transfer.
27d are sequentially arranged along the rotation direction of the photoconductor.

Each of the photoconductors 23a, 23b, 23c,
A semiconductor laser device that emits dot light modulated in accordance with image data, a deflecting device that deflects light from the semiconductor laser device in the main scanning direction, and a laser beam deflected by the deflecting device Laser irradiation devices 28a, 28b, 28c, 28d each including an f-θ lens or the like for forming an image (exposure) on the laser beam are provided. The deflecting device generally includes a rotating polygon mirror, and a mirror motor for rotating the polygon mirror at high speed is incorporated.

For example, image data corresponding to a yellow component image of a color original image is input to the laser irradiation device 28a, and image data corresponding to a magenta component image of the color original image is input to the laser irradiation device 28b. Image data corresponding to the cyan component image of the color original image is input to the irradiating device 28c.
Image data corresponding to the black component image of the color original image is input to d.

As a result, the photosensitive member 23 at each image forming position
On the a, 23b, 23c, and 23d, an electrostatic latent image corresponding to the color of the color-converted document is formed. Then, the developing device 25 of each image forming station Pa, Pb, Pc, Pd
A contains yellow toner, developing device 25b contains magenta toner, developing device 25c contains cyan toner, and developing device 25d contains black toner. Therefore, the above-described latent images corresponding to the respective colors are developed with the toners of the respective colors, and are reproduced as toner images corresponding to the color images of the document.

The first image forming station Pa
And a registration roller 12 for adsorbing the sheet to the transfer belt 13 as described above.
7, the sheet S fed through the registration roller 12 is reliably electrostatically attracted to the transfer belt 13, and in this state, the above-described first sheet is driven by the transport belt mechanism 14. To the fourth image forming stations Pa, Pb, Pc, Pd. Therefore, the sheet S is formed by the photoconductors 23a, 23a, and 23b formed at the image forming stations Pa, Pb, Pc, and Pd.
The toner images of the respective colors on 23b, 23c and 23d are sequentially transferred so as to be superimposed, and a color image is reproduced.

Then, the fourth image forming station Pd
Between the fixing device 18 and the fixing device 18, a neutralizer 29 is provided almost directly above the drive roller 15 of the transport belt mechanism 14. Therefore, the sheet S that has passed through the fourth image forming station Pd has three colors of yellow, magenta, and cyan.
The toner images of four colors including color or black are transferred in a superimposed manner.
3 is released, the sheet P is separated from the transfer belt 13 and sent to the fixing device 18. The static eliminator 29 is supplied with an AC voltage and performs an AC corona discharge to remove the charged charges.

In the color copying machine 1 having the above-described configuration, in order to form an image on a sheet, the sheet S
Are accommodated in a paper feed cassette or a tray constituting the paper feed mechanism 11 and fed one by one from the cassette or the like. The fed sheet S is stored in each of the image forming stations Pa and P
The sheet is fed to the registration roller 12 via a transfer roller or the like provided on a transfer path in order to feed the image to the image forming position of b, Pc, and Pd. The leading edge of the fed sheet P is
It is detected by a sensor (not shown) or the like, and is temporarily stopped at the above-described position of the registration roller 12 by a signal output from the sensor. Then, at a timing with each of the image forming stations Pa, Pb, Pc, and Pd, the sheet is fed to the transfer belt 13 rotating in the arrow Z direction shown in FIG. At this time, a predetermined charge is applied to the transfer belt 13 by the operation of the charging roller 17, and the sheet S is electrostatically attracted to the transfer belt 13. Thereby, while passing through the image forming stations Pa, Pb, Pc, and Pd, stable conveyance is performed in a sucked state, and the toner images of each color formed in each station are sequentially superimposed. It is transcribed.

That is, each image forming station Pa, P
b, Pc, and Pd, the toner image of each color is
3a, 23b, 23c, and 23d, which are sequentially superimposed and transferred onto the surface of the conveyed sheet P electrostatically attracted by the transfer belt 13.
When the transfer of the toner image by the fourth image forming station Pd is finally completed, the sheet S is separated from the transfer belt 13 by the action of the charge remover 29 from the leading end of the sheet S. Then, the peeled sheet S is guided to the fixing device 18, and the color toner image superimposed and transferred on the sheet S is melted and fixed, and is discharged to the paper discharge tray 21.

Hereinafter, image forming control, image processing control, operation control, and the like by the digital copying machine 1 will be briefly described.

(Explanation of Image Processing Circuit) Digital Copier 1
Converts the read data read by the reading device 4 as described above into the image forming stations Pa, Pb, and P described above.
A processing circuit for performing processing for reproducing a toner image using c and Pd will be described. Usually, the read data is R
(Red), G (green), and B (blue) color separation data,
Data that can be processed by the image forming unit 10 are Y (yellow), M (magenta), C (cyan), and K (black).
The digital copying machine 1 is provided with an image processing circuit described below in order to perform conversion processing and the like.

An image processing circuit for that purpose will be described with reference to FIG. FIG. 5 shows image data processing control excluding the image forming control of the digital copying machine 1 shown in FIG.
A data input unit 40 for inputting the read data (R, G, B data) from the input unit 8 and converting the input data into image data to be Y, M, C, K data as described above; Image processing unit 41 for performing data processing, correction processing, and the like in accordance with the conditions set forth above, and processing the processed image data into lasers of respective colors that constitute the image forming stations Pa, Pb, Pc, and Pd in the image forming unit 10. A hard disk device or a RAM that includes an image data output unit 42 for outputting to the irradiation units 28a, 28b, 28c, and 28d, and sequentially stores necessary image data and the like
An image memory 43, a central processing unit 44,
An image editing unit 45 and an external interface unit 46 are further provided.

The read data input unit 40 reads a color original image and outputs line data separated into R, G, and B color components.
A shading correction circuit 40b that corrects the line image level of the line data read by the CD 8, a line matching unit 40c such as a line buffer that corrects a deviation of the image line data read by the CCD 8, and the color of each color output from the CCD 8. A sensor color correction unit 40d that corrects the color data of the line data, an MTF correction unit 40e that corrects the change in the signal of each pixel so as to have a sharp edge, and γ that corrects the brightness of the image to correct the visibility. It comprises a correction unit 40f and the like.

The image processing section 41 includes a read data input section 4
0, or a color space correction circuit for correcting the color reproduction range of a color image signal input via an interface into a color reproduction range using color toner in the image forming unit 10, particularly the image forming stations Pa, Pb, Pc, and Pd. 41a,
And a masking circuit 41b for converting the input R, G, B data into Y, M, C data.
Then, a black area detection circuit 4 for detecting a black component from the R, G, B signals of the color data input via the read data input unit 40 or an interface described later.
1c, an undercolor removal process for detecting a black region based on the converted Y, M, and C signals output from the masking circuit 41b and a black addition process for adding a new black component word output from the black detection circuit 41c are performed. Under color removal / black addition circuit (UCR
BP) 41d, a density processing circuit 41e for adjusting the density of the color image signal based on the density conversion table, and the like. Further, the image processing unit 41 includes a scaling processing circuit 41f that performs magnification conversion of the input image information based on a preset magnification, and a character, photograph, and halftone area in the image information from the input image data. And a screen circuit 41g, etc., for detecting the image and separating the regions and determining the output pattern of the image.

Next, an image data output section 42 is provided with a laser control unit 42a for performing pulse width modulation based on the image data of each color, and a pulse width modulation signal corresponding to the image data of each color output from the laser control unit 42a. And a laser scanner unit 42b for each color that performs a recording scan with a laser based on the above. The image data output unit 42 is the laser irradiation device 28e, 28b, 28c, 28d itself described with reference to FIG. 3, and is for forming a toner image corresponding to the above-described Y, M, C, K color image data. Used for

The image memory 43 sequentially receives image data of 8 bits of 4 colors (32 bits) serially output from the image processing section 41, and temporarily stores the data in the buffer to convert the 32-bit data to 8 bits of 4 colors. And a memory control unit 43a for performing parallel output for converting the image data to four hard disks for division management and storing necessary data and the like, and recording 8-bit 4-color image data as image data for each color It comprises four hard disks (rotary recording media) 43b to be managed, and a main memory 43c comprising a RAM such as a semiconductor memory.

The central processing unit (CPU) 44 includes a read data input unit 40, an image processing unit 41, and an image data output unit 4.
2. The image memory 43, the image editing unit 45, and the external interface unit 46 are controlled based on a predetermined sequence, and the control of the image forming unit 10 and the like of the digital copying machine described later is also performed. I have.

The image editing unit 45 performs a predetermined image editing on the image data once stored in the image memory 43 via the read data input unit 40, the image processing unit 41, or the interface. .

The interface section 46 is a communication interface means for receiving image data from an external image input processing device provided separately from the digital copying machine 1. Similarly, the image data input from the interface unit 46 is also once input to the image processing unit 41, subjected to predetermined image processing, converted to a data level that can be recorded and processed by the image forming unit 10, and 43e.

(Control Circuit of Digital Copier) FIG.
4 shows a control circuit configuration for controlling the image forming unit 10 in the digital copying machine 1 shown in FIG. 4, controlling the operation panel unit, and further controlling the image processing unit.

In this circuit, each part is controlled and managed by the CPU 44. In particular, the read data input part 40, the image processing part 41, the image data output part 42 and the image memory 43 overlap with those in FIG. This is a part, and the description is omitted.

The CPU 44 controls the AD shown in FIG.
Various mechanisms constituting the digital copying machine 1, such as an F3, a reading device 4, an image forming unit 10, and a sorter unit 47 for distributing sheets, which is not described in FIG. The section and the operation section are managed by sequence control, and control signals are output to each section. The CPU 44 is connected to a board unit 48 constituting an operation panel in a mutually communicable state, and outputs a control signal in accordance with an image forming mode set by an operator or an input condition such as an image forming condition. CPU44
Side, and controls the digital copying machine 1 according to the setting mode and the setting conditions.

The CPU 44 transfers a control signal indicating the operation state of the digital copying machine to an operation board unit 48 which is an operation panel. On the operation board unit 48 side, an operation state is displayed on a display unit or the like so as to show an operator what state the apparatus is currently in by the control signal.

The external interface unit 46, which is an image data communication unit, is provided to enable information communication with other data image equipment such as image information and image control signals as described with reference to FIG.

Reference numeral 49 denotes a drive control unit such as a motor for driving the hard disk 43b described in FIG.

(Structure of Operation Panel) FIG. 7 shows an operation panel for setting the above-described image forming mode and image forming conditions of the digital copying machine. The operation panel 50 shown in FIG. 7 is provided on the operation board unit 48 described with reference to FIG.

Therefore, in the center of the operation panel 50, a touch panel (liquid crystal) display device 51 is arranged, around which keys for setting various modes and a group of keys for inputting conditions are arranged. I have. On the screen of the touch panel display device 51, there is a screen switching instruction area for constantly switching to a screen for selecting an image editing function, and various image editing functions can be selected by directly touching this area with a finger. As described above, various editing functions are listed on the display screen. By touching one of the displayed editing functions, the editing function is set.

The group of various setting keys arranged on the operation panel 50 will be briefly described. Reference numeral 52 denotes a dial for adjusting the brightness of the screen of the display device 51. Reference numeral 53 provided on the left side of the display device 51 denotes an automatic magnification setting key for setting a mode for automatically selecting a magnification.
Is a zoom key that allows the magnification to be set in 1% increments, 55
Reference numerals 56 and 56 denote fixed magnification keys for reading and selecting a preset fixed magnification, and 57 denote a same-magnification key for setting the magnification to a standard magnification, that is, equal magnification.

Reference numeral 58 provided at the lower portion of the touch panel display device 51 controls copy density adjustment from automatic to manual,
Or, a density switch key for switching to the photograph mode, 5
Reference numeral 9 denotes a density adjustment key for arbitrarily switching a density level in a manual mode or a photograph mode. Reference numeral 60 denotes a sheet for selecting a sheet size set at a position of the sheet feeding mechanism 11 of the copying machine to a desired sheet size. Select key.

A key group provided on the right side of the touch panel display device 51, that is, 61 is a copy number setting key for setting the number of copies, 62 is a button for clearing the set number of copies, etc. A clear key operated when canceling, a start key 63 for instructing a start of copying, a 64 for all releasing keys for canceling all currently set modes and conditions and returning to a display state, and a 65 for continuous copying. An interrupt key operated when a user wants to copy another document, an operation guide key 66 for operating the copier when a user cannot understand the operation of the copier, and displaying a message on the operation method of the copier, and 67 an operation guide key A message forward key for displaying the continuation of the message displayed by the operation.

Reference numeral 68 denotes a double-sided mode setting key for setting a double-sided copy mode, and 69 denotes a mode for post-processing for sorting sheets on which images have been formed discharged from the copying machine main body, such as staple, sort, and group. A post-processing mode setting key for making a selection.

Reference numerals 70 to 71 are setting keys for the printer mode and the facsimile mode.
Is a memory transmission mode key for temporarily storing a transmission original in a memory and then transmitting it. Reference numeral 71 is a copy / fax for switching the mode of the digital copying machine between copy, facsimile and printer.
A fax / printer mode switching key 72 is a one-touch dial key for storing a destination telephone number in advance and transmitting a telephone call to the destination by one-touch operation during transmission.

Next, an embodiment of a transfer device for transferring a toner image to a sheet according to the present invention will be described.

(One Embodiment of the Present Invention) The toner image transfer device according to the present invention is, as described with reference to FIG. 4, a photosensitive member 23 (23a, 23b, 23) constituting the image forming section 10.
(c, 23d), the transfer belt 13 for conveying the sheet S in contact with the sheet S, and transfer means 26 (26a, 26b, 26c, 26d) and the like.

The details of the transfer device are shown in FIG.
A transfer belt mechanism 14 including a drive roller 15 that stretches and transfers the transfer belt 13 and a driven roller 16 is provided. The transport belt mechanism 14 is provided with a charging roller 17 for electrostatically attracting the sheet sent to the transfer belt 13 via the registration roller 12, and is stable in a state where the sheet is attracted to the transfer belt 13. The transport is performed. Then, four photoconductors 23 a constituting image forming stations Pa, Pb, Pc, and Pd arranged side by side on the sheet adsorbed on the transfer belt 13 are provided.
To sequentially transfer the toner images formed on 23b, 23c, and 23d, photoconductors 23a, 23b, 23c, and 2
The transfer means 26a, 26b, 26 correspond to the area immediately below 3d.
c, 26d are provided.

The transfer means 26a, 26b, 26c, 2
6d contacts the rear surface of the transfer belt 13, that is, the surface opposite to the surface on which the sheet is adsorbed, and contacts the transfer belt 13 to the photoconductors 23a, 23b, 23c, and 23d via the sheet. I have.

Therefore, the driving roller 15 and the driven roller 16 are arranged opposite to each other (the front and rear sides in FIG. 2) of the conveyor belt mechanism 14 in a frame 14F (14R).
It is rotatably supported between them. Also, the frame 14F
In (14R), a moving member 30 is provided so as to be vertically movable in FIG. 3 with respect to the frame. The movable member 30 is provided with two rollers 31 rotatably supported so as to be located on the back side of the transfer belt 13.

The moving member 30 is provided so as to be movable within its range so as to be guided by the pin 14a provided on the frame 14F (14R) side in the long hole 30a.
A spring 32 is provided between the moving member 30 and the frame 14F (14R). Thereby, the moving member 30 is urged to move downward in FIG. Therefore, the two rotating rollers 31 provided on the moving member 30 act to press the transfer belt 13 downward from the back in FIG. As a result, the transfer belt 13 is stretched so that an appropriate tension is applied between the driving roller 15 and the driven roller 16, and the transfer belt 13 is kept in a stable state without slipping due to the rotation of the driving roller 16. Can be driven for transfer.

The transfer belt 13 which is driven stably as described above electrostatically attracts a sheet to the surface thereof by the action of the charging roller 17 and conveys the sheet to each of the image forming stations Pa, Pb and Pc. , Pd photoreceptors 23a,
The sheet is conveyed while being in contact with 23b, 23c, and 23d. At the contact positions, the toner images of the respective colors formed on the photoconductors 23a, 23b, 23c, and 23d are electrostatically transferred. Means for performing the transfer are transfer means 26a, 26b, 26c, 26
d.

The following transfer means 26a, 26b, 26
The transfer devices 26a and 2d will be described.
6b, 26c, and 26d abut against the back surface of the transfer belt 13 and transfer the transfer belt 1 with a predetermined pressure.
Pressing members 33a, 33b, 3 pressing the photoreceptor 3 toward the toner image bearing surfaces of the photoconductors 23a, 23b, 23c, 23d
3c, 33d and the pressing members 3a, 33b, 33c, 3
3d, the transfer brushes 34a, which are disposed downstream in the transfer direction of the transfer belt 13 and abut against the back surface of the transfer belt 13 toward the photoconductors 23a, 23b, 23c, 23d.
34b, 34c and 34d.

The above-described transfer means 26a, 26b, 26
c and 26d have the same configuration.
Will be described as an example.

FIG. 1 shows the details of the transfer means 26 constituting the transfer apparatus of the present invention. The transfer means 26 comprises the above-described pressing member 33 and transfer brush 34.
They are provided in a state of maintaining a predetermined positional relationship with each other in order to increase transfer efficiency. This positional relationship will be described later.

In FIG. 1, a pressing member 33 and a transfer brush 34 that constitute the transfer member 26 are fixedly supported by an L-shaped support plate 35 made of, for example, an insulating member. Is movable with respect to an insulating mounting member 36 fixed between the frames 14F and 14R of the transport belt mechanism 14, that is, mounted to be vertically movable in FIG. The attachment member 36 is provided with a compression spring 37 as an urging means for urging the transfer member 26 to move upward between the bottom surface and the support plate 35.

Therefore, the support plate 35 is
7, the pressing member 33 moves upward.
Presses the back surface of the transfer belt 13 toward the photosensitive member 23 with the urging force of the spring 37. Therefore, a contact area (nip portion) having a predetermined width is formed between the surface of the photoconductor 23 and the sheet suction surface side of the transfer belt 13. The transfer brush 34 of the transfer member 26 is brought into contact with the back surface of the transfer belt 13 in the contact area by the urging force of the spring 37.

The transfer brush 34 is a conductive brush and is made of a known material. Then, a predetermined transfer potential is supplied to the conductive transfer brush 34 via a control circuit, and stop control is performed. Further, the pressing member 33 is not limited to a conductive or insulating member, but may be made of any material.

By providing the transfer means 26 having such a configuration, the sheet can be brought into contact with the surface of the photoreceptor 23 through the transfer belt 13 in a predetermined width area, and the transfer brush 34 is brought into contact in that area. Therefore, the transfer of the toner image can be favorably performed. In other words, the contact width between the sheet and the photoconductor 23 can be arbitrarily set by providing the pressing member 33 in a predetermined region, and efficient transfer in that region can be performed.

The support plate 35 has a plurality of long holes formed in the direction of the rotation axis of the photosensitive member.
A boss portion such as a step screw 38 fixed to 6 is inserted into the mounting member 36 so as to be movable within a long hole, that is, vertically movable in FIG. Instead of such a configuration, a conventionally known moving mechanism may be arbitrarily used.

The principle, that is, the reason why the transfer of the toner image is favorably performed by providing the transfer means 26 having the structure shown in FIG. 1 will be described below. In other words, the setting of the positional relationship between the pressing member 33 and the transfer brush 34 for favorably transferring the toner image by the configuration of the transfer device of the present invention, and the reason why the toner image is favorably and efficiently transferred at that time. In particular, the principle will be described. Therefore, it is necessary to set the positional relationship between the pressing member 33 and the transfer brush 34 as described below, and to arrange the transfer brush 34.

Therefore, as shown in FIG. 2, the transfer means 26 of the present invention described with reference to FIG. 1 transfers the transfer belt 13 to the photoreceptor 23 via the sheet S in a predetermined area of the contact area (nip). Pressing member 33 so that L can be set
Is provided. The range of the contact area L is determined by the pressing member 33.
Can be arbitrarily set depending on the mounting position, the biasing state, and the like of the.

In the contact area L where the transfer belt 13 contacts the photoreceptor 23 via the sheet, the transfer brush 34 is contacted on the downstream side after the midpoint P which divides the transfer belt 13 into two.
Each of the pressing members 33 and the transfer brush 34 is mounted on the mounting member 36 while maintaining a positional relationship such that the pressing member 33 and the transfer brush 34 are separated from each other.
That is, the transfer brush 34 is not brought into contact with the initial upstream side where the transfer belt 13 is brought into contact with the pressing member 33,
It is arranged and configured so as to make contact on the downstream side with the point P as a boundary.

As described above, by providing the transfer brush 34, the transfer brush 34 contacts the transfer belt 13 in a state in which the transfer belt 34 is sufficiently adapted after the sheet S starts to contact the photosensitive member 23 on the transfer belt 13. The transfer is started from the point of contact. In other words, the toner image on the photosensitive member 23 comes into contact with the sheet on the transfer belt 13 gradually from the position of the pressing member 33, and is subjected to the transfer operation by the transfer brush 34 after the contact state is adjusted. The image is transferred in a good condition without being disturbed by the sheet. As a result, good transfer can be performed without deteriorating the image quality due to toner disturbance.

In particular, as described in the present invention, when a color image is formed, the previous toner image is transferred to a sheet, and when the next toner image is transferred while being superimposed on the previous toner image, the first toner image is transferred first. After the next toner image sufficiently overlaps the used toner image and becomes familiar, the transfer of the toner image by the transfer brush 34 can be performed. As a result, deviation during transfer,
Deterioration of image quality due to toner disturbance or the like can be prevented, and a high-quality image can be obtained.

Further, the fact that the transfer state according to the present invention is excellent will be described with reference to FIG. Even when the transfer belt 3 is pressed against the photoconductor 23 by the pressing member 33 as shown in FIG.
At the starting point a in the contact area L, as shown in the figure, the two are not in good contact with each other, and there is a case where a floating or the like occurs due to some gap. Therefore, if the transfer brush 34 comes into contact with the transfer belt 13 from the start point a of the contact area L and performs a transfer operation, the toner image formed on the photoconductor 23 side is sucked and transferred to the sheet S side. At this time, if the transfer is performed in the separated portion due to the floating of the gap or the like, the transfer position is shifted, or the toner is transferred to a different position where the flying toner can be sufficiently controlled,
Good transfer is not performed, and the toner image is disturbed.

However, as shown in FIG. 2, in the present invention, the transfer brush 34 is brought into contact with the transfer belt 13 and the photoreceptor 23 after the middle point P of the contact area L.
Since the transfer operation is started after the sheet S is completely in contact with the photoconductor 23 and the contact state is sufficiently adjusted, good transfer can be performed without the above-described disturbance of the toner image. .

Further, at the downstream of the contact area L between the transfer belt 13 and the photosensitive member 23, particularly at the end point b of the transfer area L, even if a separation point occurs similarly to the start point a, the transfer belt 13 remains at that position. Even when the transfer brush 34 comes into contact with the transfer brush 34 and the transfer operation is continuously performed, the transfer is sufficiently completed at the time of contact with the transfer brush 34 after the previous middle point P, that is, the transfer to the sheet side. Has been completed (most of the transfer has been completed). Therefore, even if the transfer operation is continued at the separated portion, the transfer of the toner image is not performed, and there is no problem.

That is, at the separation point at the end point b where the contact between the two ends on the downstream side, the transfer of the toner image is completed even if the transfer brush 34 contacts the transfer belt 13 and the transfer operation is continued. As a result, the toner image is not transferred at this time, and the transfer of the toner image is not disturbed, resulting in good transfer.
Therefore, the transfer brush 34 is moved between the transfer belt 13 and the photoconductor 2.
The same effect can be expected even in a case where the contact area 3 is contacted downstream from the contact area L. Therefore, the transfer brush 34
After the middle point P downstream, there is no need to improve the accuracy of the arrangement position of the transfer brush 34 so much, and the transfer brush 34 can be easily achieved with the arrangement configuration. Further, if the contact area L between the transfer belt 13 and the photoconductor 23 cannot be sufficiently ensured, the transfer belt 13 may come into contact with the downstream side which is out of the contact area L. Can be performed.

Next, in the present invention, in the contact area L between the photosensitive member 23 and the transfer belt 13 via the sheet S, various aspects in a state where the transfer brush 34 is in contact with the downstream side of the midpoint P will be described below. explain.

As described with reference to FIG. 2, the transfer brush 34 may be arranged so that the brush tip comes into contact after the midpoint P of the contact area L. Therefore, FIG.
As shown in (a), the transfer brush 34 is arranged so that one end side of the transfer brush 34, that is, the upstream end in the moving direction of the transfer belt 13 corresponds to the middle point P of the contact area L. At this time, since the transfer brush 34 is provided so as to be pressed against the transfer belt 13, the point of contact with the transfer belt 13 is further downstream of the middle point P due to the bending of the brush. Even in such a case, the transfer state can be properly performed. In this case, on the downstream side of the transfer brush 34, the transfer brush 34 may be in contact with the transfer belt 13 even when the contact state between the transfer belt 13 and the photoconductor 23 is released, that is, at a point outside the contact area L. Even in such cases, transfer failure does not occur as described above, and good transfer is possible.

As shown in FIG. 8B, a part of the transfer brush 34 (the upstream end in the transfer belt transport direction).
However, in a state where the upstream side of the intermediate point P is located, the transfer brush 3
4, the transfer brush 34 is pressed against the transfer belt 13 and bends.
Contact position on the downstream side of the midpoint P. Even in such a case. As described above, the transfer state can be favorably performed. Further, the transfer belt 13 is driven in the direction in which the sheet S is conveyed, so that the transfer operation is performed by the transfer brush 34. Therefore, the transfer brush 34 is entirely collapsed in the moving direction of the belt 13 in the conveying direction by friction.

Therefore, in the transfer brush 34,
There is a margin in setting the arrangement position, no severe design or the like is required, and the object of the present invention can be sufficiently achieved simply by the arrangement configuration.

(Another Mode of Transfer Means According to One Embodiment of the Present Invention) The transfer means 26 as shown in FIG. 1 supports the pressing member 33 and the transfer brush 34 on the same support plate 35 and applies the same bias. The device 37 is configured to urge and press the transfer belt 13 from the rear side. Instead of such a configuration, for example, a configuration as shown in FIGS. 9A and 9B may be employed.

In particular, according to the transfer member 26 shown in FIG.
The pressing member 33 and the transfer brush 34 are simultaneously transferred to the transfer belt 1.
3 is urged toward the photoconductor 23 from the back side. In FIG. 9A, the pressing members 33 and the transfer brushes 34 are urged individually. is there. FIG. 9B shows a configuration in which the pressing member 33 is pressed in a fixed state and only the transfer brush 34 is urged.

First, the structure of FIG. 9A will be described. The pressing member 33 is attached to the mounting member 3 made of, for example, an insulating material.
6 is mounted so as to be directly movable. Therefore, a plurality of long holes are formed in the pressing member 33 in the rotation axis direction of the photoconductor 23. A pin 38a having a stopper to guide the elongated hole is fixed to the mounting member 36, and the pressing member 33 is provided along the pin 38a so as to be vertically movable within the elongated hole. An urging spring 37a is interposed between the bottom plate of the mounting member 36 and the bent bottom of the pressing member 33. As a result, the transfer belt 33 is urged toward the photoreceptor 23 at the bent end portion of the pressing member 33.

The transfer brush 34 is connected to the transfer belt 13.
The support 35a is fixed to the support 35a facing
Is provided so as to be guided by the pin 38b so as to be vertically movable with respect to the mounting member 36 as described with reference to FIG. Therefore, a plurality of long holes are formed in the standing piece of the support 35a at intervals in the rotation axis direction of the photoconductor 23, and the long holes are inserted into the pins 38b provided with the falling-off preventing members. I have. A spring 37b for urging upward is interposed between the bottom plate of the mounting member 36 and the back surface of the support 35a to which the transfer brush 34 is fixed. Accordingly, the support 35a is biased toward the transfer belt 13 by the bias of the spring 37b, and the transfer brush 34 is pressed against the rear surface of the transfer belt 13 with an appropriate pressure.

With this configuration, the pressing member 33
In addition, the pressing state of the transfer brush 34 against the back surface of the transfer belt 13 can be set individually. That is, in the pressing member 33, the contact area L where the transfer belt 13 and the photoconductor 23 come into contact via the sheet can be easily set to a predetermined width. Further, in a range where the transfer belt 13 and the photoconductor 23 are in contact with each other with a predetermined width, the transfer brush 34 can be pressed against the transfer belt 13 with an appropriate pressure, and further improvement in transfer efficiency can be expected. .

With the structure shown in FIG. 9A,
The pressing member 33 alone can press and urge the transfer belt 13,
The sheet S is brought into good contact with the photoreceptor 23 in a contact area L that can be formed between the sheet S and the photoreceptor 23 regardless of the difference in the material of the sheet S, for example, thickness, stiffness, and material. And stable transfer can be achieved. In addition, since the transfer brush 34 is independently pressed against the transfer belt 13, the pressed state can be maintained in a good condition, which is one factor that can improve transfer efficiency.

Further, the transfer member 2 having the structure shown in FIG.
6 shows the transfer belt 1 with the pressing member 33 shown in FIG.
The only difference is the configuration for urging the rear surface of No. 3 toward the back, and the other configurations are the same. That is, in the transfer member 26, the pressing member 33 presses the transfer belt 13 from the back surface to the photoconductor 23 side by using its own elasticity or spring property. Therefore, the pressing member 33 is formed of an elastic member or a spring member, and a portion obtained by bending the end opposite to the front end pressing the transfer belt 13 is fixed to, for example, the bottom surface of the mounting member 36, and the free end of the front end is fixed. The side is provided so as to press against the back surface of the transfer belt 13.

Also in such a configuration, similarly, the back surface of the transfer belt 13 is urged toward the photosensitive member 23 by the pressing member 33, and the width of the contact area (nip portion) between the transfer belt 13 and the photosensitive member 23 is increased. Can be maintained in a predetermined state, and the transfer brush 34 can be pressed against the contact area L with a moderate pressure. Thereby, the same transfer efficiency as in the case of FIG. 8A can be expected.

(Another Aspect of Transfer Brush in One Embodiment of the Present Invention) The transfer brush 34 described with reference to FIG.
The flat portion is pressed against the transfer belt 13. Therefore, the transfer brush 34 comes into contact with its width, that is, the same width in the moving direction of the transfer belt 13.

A mode in which the transfer brush 34 can be further improved and the transfer efficiency can be further improved will be described with reference to FIG. That is, the transfer brush 34 as shown in FIG.
The transfer brush 34 may be formed in a shape as shown in FIG.

First, the transfer brush 34 shown in FIG.
The front end portion of the transfer belt 13 that is in contact with the rear surface is long on the upstream side in the moving direction of the transfer belt 13 and is gradually shortened on the downstream side. The transfer brush 34 having such a shape is brought into contact with the transfer belt 13 and the transfer belt 13
Is driven to move, the transfer brush 34 falls down in the moving direction, and the transfer brush 34 comes into contact with the transfer belt 13 such that the transfer brush 34 concentrates on the downstream side of the middle P of the contact area L.

For this reason, the transfer belt 13 and the transfer brush 3
4, the density of the contact state with the photosensitive drum 23 becomes high, and the contact portion can be concentrated. Thus, the transfer efficiency can be increased. The concentrated portion is located downstream of the middle point P of the contact area L as described above, and is a contact position. Therefore, the transfer efficiency is increased, and the toner image is excellently printed on the sheet and the image quality is disturbed. No good transfer is possible.

In FIG. 10B, the tip of the transfer brush 34 is formed flat as it is. A pedestal 35a on the support 35 side on which the transfer brush 34 is mounted.
Is provided so as to be inclined downward along the moving direction of the transfer belt 13. Even when the transfer brush 34 is fixed to the pedestal 35a, the same operation and effect as those of the structure shown in FIG. That is, as in the case where the transfer brush 34 is formed as shown in FIG. 10A, the tip end of the brush 34 comes into intensive contact with the transfer belt 13, so that good transfer efficiency can be improved.

However, according to the configuration of FIG. 10B, since the transfer brush 34 is inclined along the moving direction of the transfer belt 13, the transfer brush 34 bends favorably in that direction, and It can be expected that the contact state with the satisfactorily performed. Further, since the tip of the transfer brush 34 can be formed flat, it is advantageous in that the manufacturing thereof is simplified. The components shown in FIGS. 10A and 10B can be selected as needed, and are not limited to either one.

[0112]

According to the transfer device of the image forming apparatus of the present invention, the sheet is brought into contact with the image carrier via the transfer belt.
The transfer state is improved when the transfer brush is brought into contact with the transfer belt from the rear side of the transfer belt to improve the transfer state. In particular, the upstream side is used to secure a contact area where the image carrier and the sheet are brought into contact via the transfer belt. Side, the transfer brush is brought into contact with the middle point of the contact area on the downstream side, so that the toner image on the image carrier is not disturbed.
Since the transfer is performed after the sheet has been closely adhered to the sheet, the transfer is performed satisfactorily and efficiently.

In addition, the transfer brush may be moved downstream of the middle point of the contact area in contact with the transfer belt, and in consideration of the bending of the brush and the movement of the transfer belt, the arrangement position of the transfer brush downstream of the middle point is considered. Is not severe, and can be performed with a simple arrangement setting to transfer a good tenor image.

If the tip of the transfer brush is inclined or the pedestal or the like on which the transfer brush is mounted is provided so as to be inclined, concentrated contact at the contact area of the photoconductor with the transfer belt becomes possible. Transfer efficiency increased,
Good transfer can be expected.

Here, if the transfer device of the present invention is applied to a device for forming a color image, the transfer after the toner image previously transferred and the toner image to be transferred next are well adapted. Is performed, good transfer and good image quality can be provided without bleeding or disturbance of color.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a transfer unit constituting a transfer device according to an embodiment of a transfer device of the present invention.

FIG. 2 is a cross-sectional view illustrating a positional relationship of a transfer unit included in the transfer device according to the embodiment of the present invention and explaining a reason why transfer is favorably performed.

FIG. 3 is a side view showing the overall configuration of the transfer device according to the present invention.

FIG. 4 is a diagram showing an internal configuration of a digital copying machine as a color image forming apparatus provided with the transfer device of the present invention.

FIG. 5 is a block diagram showing a control configuration of a color image processing circuit of the digital copying machine shown in FIG.

6 is a block diagram showing an overall control circuit configuration of the digital copying machine shown in FIG.

7 is a plan view showing an example of an operation panel for arbitrarily setting various conditions, modes, and the like of the digital copying machine shown in FIG.

FIG. 8 is a cross-sectional view illustrating an example of each aspect of a transfer unit according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating a pressing biasing mode of a pressing member and a transfer brush constituting a transfer unit according to an embodiment of the present invention.

FIG. 10 is a view for explaining a configuration of another embodiment of a transfer brush constituting a transfer unit according to an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 digital copying machine 2 platen 3 automatic document feeder (ADF) 4 reading device 10 image forming unit 11 paper feed mechanism 13 transfer belt (sheet holding body) 14 transport belt mechanism (transfer belt holding mechanism) 15 drive roller 16 driven Roller 17 charging roller 23 photoreceptor (image carrier) 26 transfer means 29 static eliminator 33 pressing member 34 transfer brush 35 support 35a pedestal 36 mounting member 37 spring (biasing means) S sheet L contact area P middle point

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masashi Hirai 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Kiyoshi Toizumi 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Osamu Nakayama 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Sharp Corporation (72) Inventor Koichi Nakamura 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka F Terms (reference) 2H030 AB02 BB46 2H032 AA05 BA18

Claims (5)

[Claims] 1. A sheet holder for transferring a toner image formed on an image carrier to a sheet, the sheet holder holding the sheet, and transporting the sheet to a transfer position in contact with the image carrier. A transfer device for applying a transfer potential to the back side opposite to the sheet holding surface, and transferring a toner image formed on the image carrier onto the held sheet; The transfer means includes a pressing member for securing a contact area for bringing the sheet holding body into contact with the image carrier through a sheet in a predetermined range, and the contact area on the downstream side of the pressing member in the moving direction of the sheet holding body. A transfer brush that is in contact with the back surface of the sheet holding member, wherein the transfer brush is disposed so as to contact the sheet holding member downstream of a midpoint obtained by dividing the contact area into two. Image The transfer device of forming apparatus. 2. A method according to claim 1, wherein said transfer brush, said pressing member, or said transfer brush and said pressing member are pressed against said back side of said sheet holding member by pressing means. The transfer device for an image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the transfer brush is arranged so as to be in contact with the transfer belt on a downstream side with respect to a center point of the contact area in consideration of the bending of the brush itself. Transfer device. 4. The transfer brush according to claim 1, wherein a front end portion of the transfer brush that comes into contact with the sheet holding member has an upstream end in a moving direction of the sheet holding member.
2. The transfer device according to claim 1, wherein the transfer device is formed so as to protrude from the downstream side. 5. A pedestal attached to a support for pressing the transfer brush against the sheet holder, the pedestal being formed to be inclined downstream in the moving direction of the sheet holder. The transfer device of the image forming apparatus described in the above.