JP3857101B2 - Transfer device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transfer device and an image forming apparatus, and more particularly to a transfer position misalignment prevention structure when an image is superimposed and transferred using a belt-like transfer body.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine, a facsimile, a printer, or a printing machine, a visible image carried on a photosensitive member that is a latent image carrying member is transferred to a transfer member.
In addition to a recording sheet that directly faces and contacts the photosensitive member, a belt-like transfer member may be used as the transfer member. One of the latter cases is multicolor image formation including full color.
As a configuration for forming a multicolor image, an electrostatic latent image for each color separation color is formed using one photoconductor as a latent image carrier and each photoconductor using a plurality of photoconductors. In some cases, an electrostatic latent image corresponding to the color separation color is formed.
When one photoconductor is used, a single charging device, writing device, and transfer device are provided for the photoconductor, and toner of a color complementary to the color separation color formed by the writing device can be supplied. A number of developing devices corresponding to the number of color separations, and performing visible image processing of the electrostatic latent image by supplying toner from a developing device of a color corresponding to the electrostatic latent image formed on the photoreceptor, A process is employed in which a composite toner image is formed on a photoconductor and then the composite toner image is transferred to a recording sheet.
In the case of using a plurality of photoconductors, each image forming unit includes an image forming unit including an apparatus that performs image forming processing for each photoconductor, that is, a device that performs each process of charging, writing, and developing. The toner images formed in step 1 are superimposed and transferred to the intermediate transfer member in sequence and transferred to the recording sheet at once, or the recording sheet is conveyed to the position of each image forming unit and directly superimposed on the recording sheet during the conveyance process. The transfer process is adopted.
[0003]
When one photoconductor listed above is used, the size of the apparatus can be reduced because the number of photoconductors is small. On the other hand, an electrostatic latent image corresponding to a color for each color separation targeting one photoconductor. There is a problem that the time until a multicolor image is obtained becomes longer by repeating the process of forming the image. On the other hand, when a plurality of image forming units mentioned in the latter are used, there is an advantage that the image forming process can be speeded up by performing the image forming process in parallel in each image forming unit.
[0004]
On the other hand, as a configuration in the case of using the plurality of image forming units mentioned above, there are configurations shown in FIGS.
The configuration shown in FIGS. 3 and 4 is different in the transfer method of the image formed in the image forming unit. In the configuration shown in FIG. 3, each image forming unit A1 to A4 and the photosensitive in each of these image forming units A1 to A4 are used. The toner images formed by the respective image forming units are directly applied to the recording sheet S (shown by arrows indicating the moving direction for convenience) electrostatically adsorbed on the conveyance belt C that can move to face the bodies B1 to B4. By being transferred, the toner images of the respective colors are superimposed and transferred onto the recording sheet S.
[0005]
In the configuration shown in FIG. 4, the toner images of the respective colors formed by the image forming units A1 to A4 are respectively applied to an intermediate transfer belt D as an intermediate transfer member facing the photoreceptors B1 to B4 in the image forming units A1 to A4. The composite toner image that is superimposed and transferred and carried on the intermediate transfer belt D is collectively transferred to the recording sheet S. In the transfer system used in the configuration shown in FIG. 4, the transfer to the intermediate transfer member is often referred to as primary transfer, and the transfer to the recording sheet is often referred to as secondary transfer.
[0006]
As shown in FIG. 4, when the intermediate transfer belt D is used as an intermediate transfer member, a configuration including a driving roller D1, a driven roller D2, and a tension roller D3 disposed between these rollers is used. Transfer members E1 to E2 for transferring visible images formed on the image forming units A1 to A4 are provided at positions facing the photoconductors B1 to B4 in the image forming units A1 to A4. . In FIGS. 3 and 4, symbol F indicates a discharge conveyance belt, and symbol G indicates a fixing device.
[0007]
[Problems to be solved by the invention]
When a belt is used as a conveying belt or an intermediate transfer member as a member used when transferring a toner image formed on a photoreceptor in an image forming unit, it is possible to align the transfer positions of the images. This is important in preventing the occurrence of uneven color.
[0008]
In particular, in the case of a configuration called a tandem system in which the respective image forming units are juxtaposed in the belt extending direction as in the configuration shown in FIG. 4, the belt stretches or the eccentricity of the roller around which the belt is wound. As a result, the moving state of the belt is likely to change, and this may cause the transfer position between the image forming units to shift.
[0009]
In order to align the transfer position in each image forming unit with the image transfer position on the belt, for example, the distance (P1) between the image transfer positions indicated by the symbol P in FIG. It is conceivable to set it to an integral multiple of the circumference of the roller (the roller indicated by D1 in FIG. 4). As a result, even if the roller is decentered, the phase of one rotation cycle speed fluctuation of the roller coincides at each transfer position, and it is possible to obtain a state in which there is almost no image displacement. In other words, the speed fluctuation phase of the transfer body at the image transfer position of the first color is made the same at the image transfer positions of the second and subsequent colors, so that the speed fluctuation at each image transfer position matches. Further, it is possible to eliminate the expansion and contraction of the transfer body due to the change in speed at each image transfer position.
[0010]
However, the above-mentioned conditions are based on the premise that the belt has a uniform thickness. If the thicknesses are different, the peripheral speed around the roller is maintained even if this condition is set. As a result, the moving speed of the belt changes, and as a result, the image transfer position of the belt with respect to the transfer position in each image forming unit may shift.
[0011]
5 to 7 are diagrams for explaining the reason why the above phenomenon occurs. In FIG. 5, it is difficult to set the belt D used to a uniform thickness in terms of processing accuracy, and the thickness varies (ta> tb).
If the thickness varies, the moving speed of the belt on the drive roller D1 varies as shown in FIGS. That is, in the case shown in FIG. 6, since the portion thicker than the other portions is wound around the drive roller D1, the peripheral speed at this time is the radius (R of the drive roller D1 around which the belt is wound). ) And the average of the belt side thickness on the basis of 1/2 to 1/3 of the belt thickness is obtained by the product of the radius and the angular velocity (ω). In each case, the peripheral speeds (Va, Vb) can be obtained by the following formulas 1 and 2.
Va = {roller radius (R) + belt thickness (ta / 2)} × ω (1)
Vb = {roller radius (R) + belt thickness (tb / 2)} × ω ·· (2)
Here, regarding the thickness, since ta> tb, the peripheral speed (Va, Vb) is Va> Vb.
From this result, due to the difference in thickness, the moving speed of the belt stretched portion, that is, the portion reaching the transfer position, changes according to the change of the moving speed when the drive roller D1 rotates.
[0012]
It is necessary to eliminate the difference in thickness in order to eliminate changes in the moving speed of the belt. However, actual belts are inevitably subject to variations in processing, and the transfer position of each image forming unit is not guaranteed. At present, it is difficult to match the image transfer positions on the belt. For this reason, even if the dimensional accuracy of the driving roller and the elongation of the belt are suppressed, the speed variation due to the thickness variation cannot be suppressed, so that there is a possibility that the transfer positions do not coincide with each other and color misregistration occurs.
[0013]
An object of the present invention is to provide a transfer device having a configuration capable of preventing the occurrence of a defective image such as color misregistration by preventing the image transfer position from deviating in view of the problems in the case of using the above-described conventional transfer device, in particular, a belt. An apparatus and an image forming apparatus are provided.
[0014]
[Means for Solving the Problems]
According to the first aspect of the present invention, images of different colors subjected to visible image processing on a plurality of latent image carriers are sequentially transferred to a transfer body using a single belt passing through the position of each latent image carrier. The belt is wound around at least one pair of rollers and driven by a driving source different from the rollers , and the driving source has a flat portion having no curvature in the belt. A driving roller opposed to be sandwiched and a counter roller forming a followable pressurizing means, wherein the diameter of the counter roller is set to be approximately an integral fraction (1 / n) of the diameter of the driving roller, The circumferential length of the driving roller in the driving source is set to be an integral number (1 / n) of the arrangement interval of the latent image carriers .
[0015]
According to a second aspect of the present invention, in the transfer device according to the first aspect, the arrangement position of the driving source is set on the upstream side in the moving direction of the belt with respect to the transfer position of the image on the flat portion of the belt. It is characterized by that.
[0016]
According to a third aspect of the present invention, the transfer device according to the first or second aspect is used in an image forming apparatus .
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram of an image forming apparatus to which a transfer apparatus according to an embodiment of the present invention is applied. The image forming apparatus shown in FIG. 1 has a latent image carrier capable of forming an image of a color corresponding to color separation. It is equipped with a tandem configuration in which a plurality of photoconductors are juxtaposed, and a toner image formed on each photoconductor is transferred onto an intermediate transfer body, and then the superimposed image is collectively transferred to a sheet such as recording paper This is a color printer capable of forming a multicolor image. In the present invention, the image forming apparatus is not limited to a color printer, but of course includes a color copying machine, a facsimile machine, and a printing machine.
[0021]
In FIG. 1, in a color printer 1, an image forming unit 1A is positioned at a central portion in the vertical direction, a document feeding unit 1B is provided below the image forming unit 1A, and an original document table 1C1 is provided above the image forming unit 1A. Each of the scanning units 1C is arranged.
An intermediate transfer belt 2 having a horizontally extending surface is disposed in the image forming unit 1A, and a configuration for forming an image of a color having a complementary color relationship with the color separation color above the intermediate transfer belt 2 Is provided.
[0022]
In the image forming unit 1A, photoreceptors 3B, 3Y, 3C, and 3M capable of carrying images of toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the extended surface of the intermediate transfer member 2. Has been. In the following description, in the case of contents common to all the photoconductors, the photoconductor is denoted by reference numeral 3.
Each of the photoconductors 3B, 3Y, 3C, and 3M is composed of a drum that can rotate in the same direction (counterclockwise in FIG. 1). A device 4, a writing device 5, a developing device 6, a primary transfer device 7, and a cleaning device 8 are disposed (for convenience, the reference numeral of each device is indicated by B for the photoreceptor 3B). .
[0023]
The intermediate transfer belt 2 corresponds to a primary transfer portion to which a visible image from an image forming unit including each photoconductor is sequentially transferred. The intermediate transfer belt 2 is wound around a plurality of rollers 2A to 2C and is connected to the photoconductor. A roller 2C, which is configured to be movable in the same direction at the facing position and is different from the rollers 2A and 2B constituting the stretched surface, faces the secondary transfer device 9 with the intermediate transfer belt 2 interposed therebetween. In FIG. 1, reference numeral 10 indicates a cleaning device for the intermediate transfer belt 2.
[0024]
The secondary transfer device 9 includes a transfer belt 9C that is wound around the charging drive roller 9A and the driven roller 9B and is movable in the same direction as the intermediate transfer belt 2 at the secondary transfer position where the secondary transfer device 9 is located. The multi-color image superimposed on the intermediate transfer belt 2 in the process of transporting the recording sheet while electrostatically attracting it by charging the transfer belt 9C with the charging drive roller 9A can be transferred by single transfer or carried by a single color. Each image can be transferred to a recording sheet.
[0025]
A recording sheet is fed from the paper feeding unit 1B to the secondary transfer position.
The paper feed unit 1B includes a plurality of paper feed cassettes 1B1, a plurality of transport rollers 1B2 arranged in a transport path for recording sheets fed from the paper feed cassette 1B1, and a registration roller 1B3 positioned in front of the secondary transfer position. I have. In this embodiment, in addition to the conveyance path of the recording sheet fed out from the sheet feeding tray 1B1, a recording sheet of a type not stored in the sheet feeding cassette 1B1 is fed to the sheet feeding unit 1B toward the secondary transfer position. This configuration includes a manual feed tray 1A1 and a feeding roller 1A2 provided with a part of the wall surface of the image forming unit 1A that can be turned up and down.
In the middle of the conveyance path of the recording sheet from the sheet feeding cassette 1B1 to the registration roller 1B3, the conveyance path of the recording sheet fed out from the manual feed tray 1A1 joins, and the recording sheet fed from any conveyance path is also a registration roller. Registration timing is set by 1B3. The registration roller 1B3 is usually used while being grounded, but a bias may be applied to remove paper dust from the recording sheet for the purpose of removing paper dust.
[0026]
The writing device 5 (indicated by reference numeral 5B in FIG. 1 for convenience) has image information obtained by scanning a document on the document table 1C1 included in the document scanning unit 1C or an image output from a computer (not shown). The writing light is controlled by the information, and an electrostatic latent image corresponding to the image information is formed on the photoreceptors 3B, 3Y, 3C, and 3M.
[0027]
The document scanning unit 1C is provided with a scanner 1C2 that exposes and scans the document on the document table 1C1, and an automatic document feeder 1C3 is disposed on the upper surface of the document table 1C1. The automatic document feeder 1C3 has a configuration capable of reversing the document fed on the document table 1C1, and can perform scanning on both sides of the document.
[0028]
An electrostatic latent image formed on the photoconductor 3 (members indicated by reference numerals 3B, 3Y, 3C, and 3M in FIG. 1) formed by the writing device 5 is indicated by reference numeral 6B in FIG. 1 for convenience. ) To be subjected to a visible image processing and primary transfer to the intermediate transfer belt 2. When the toner images for the respective colors are superimposed and transferred onto the intermediate transfer belt 2, the secondary transfer device 9 performs secondary transfer on the recording sheet at once.
[0029]
The unfixed image carried on the surface of the recording sheet that has been secondarily transferred is fixed by the fixing device 11. Although not shown in detail, the fixing device 11 includes a belt fixing structure including a fixing belt heated by a heating roller and a pressure roller facing and abutting the fixing belt, and the contact between the fixing belt and the pressure roller. By providing the area, that is, the nip area, the heating area for the recording sheet can be expanded as compared with the fixing structure of another roller type.
The recording sheet that has passed through the fixing device 11 is switched in the transport direction by a transport path switching claw 12 disposed behind the fixing device 11, and is transported toward the paper discharge tray 13 and reversely transported. A transport direction is selected for the path RP.
[0030]
The intermediate transfer belt 2 collectively transfers the superimposed and transferred images, and then the residual toner is removed by the cleaning device 10 to prepare for the primary transfer again.
[0031]
In the color printer 1 having the above-described configuration, the document placed on the document table 1C1 is exposed and scanned, or the image of the image information from the computer is used for statically charging the photosensitive member 3. After the electrostatic latent image is formed and the electrostatic latent image is subjected to visible image processing by the developing device 6, the toner image is primarily transferred to the intermediate transfer belt 2.
[0032]
The toner image transferred to the intermediate transfer belt 2 is transferred as it is to the recording sheet fed out from the paper feed unit 1B in the case of a single color image, and the primary transfer is repeated in the case of a multicolor image. And then secondarily transferred to the recording sheet at once. The recording sheet after the secondary transfer is fixed with an unfixed image by the fixing device 11 and then fed to the paper discharge tray 13 or reversed and fed again toward the registration roller 1B3.
[0033]
The intermediate transfer belt 2 forming the primary transfer portion and the drive structure thereof are shown in FIG.
In FIG. 2, although not shown in detail, the intermediate transfer belt 2 is composed of a base layer made of a base material made of a material that hardly stretches, such as a fluorine-based resin having a small elongation or a rubber material having a large elongation, and a canvas. And an elastic layer made of fluorine-based rubber or acrylonitrile-butadiene copolymer rubber provided on the upper surface. The surface of the elastic layer is provided with a coat layer that is coated with a fluororesin to improve smoothness.
[0034]
The intermediate transfer belt 2 is wound around at least a pair of support rollers 2A and 2B and a roller 2C having a backup function, and is driven by the counterclockwise rotation of the drive roller 2A.
A surface extended between the support rollers 2A and 2B, that is, a plane having no curvature, faces the photoreceptors 3B, 3Y, 3C, and 3M of each image forming unit. A transfer roller 2D for electrostatically transferring a visible image on the photoconductor is disposed at a position facing each photoconductor with the intermediate transfer belt 2 interposed therebetween.
[0035]
The intermediate transfer belt 2 is driven by a drive source provided separately from the support rollers 1A, 2B, and 2C. The configuration will be described below with reference to FIG.
The drive source is opposed to the drive roller 14 and the drive roller 14 disposed on a flat surface having no curvature upstream of the image transfer position for each image forming unit in the moving direction of the intermediate transfer belt 2 and the intermediate transfer belt 2 therebetween. And the counter roller 15. The drive roller 14 is driven to rotate by a drive motor 16 to drive the intermediate transfer belt 2.
[0036]
The counter roller 15 is given a habit of pressing the intermediate transfer belt 2 toward the drive roller 14 by an elastic body 17 such as a spring. For this reason, the intermediate transfer belt 2 is driven between the driving roller 14 and the opposing roller 15 so that the rotational force is well transmitted using the frictional force with the driving roller 14. ing.
[0037]
The configuration of the driving roller 14 and the counter roller 15 is as follows.
[0038]
(1) The drive roller 14 is an integral number (1 / n) of the arrangement interval P1 between the image transfer positions where the photosensitive member 3 and the intermediate transfer belt 2 face each other in each image forming unit. The circumference that becomes the relationship of is set.
(2) The counter roller 15 is set to a diameter that is 1 / n of an integer with respect to the diameter of the drive roller 14.
According to the conditions listed in (1), even when the drive roller 14 is eccentric or uneven in speed, the occurrence cycle of eccentricity or uneven speed can be made to coincide between image transfer positions in the image forming unit. . That is, if the speed fluctuation period caused by the difference in thickness existing in the intermediate transfer belt 2 is made the same at each image transfer position, the speed deviation at each image transfer position can be eliminated. The speed change at the time when the image transfer position is reached can be matched between the image transfer positions, so that the shift of the image transfer position does not occur. As a result, it is possible to eliminate the color shift caused by the image transfer position shift.
[0039]
According to the conditions listed in (2), even when periodic speed fluctuations of the facing roller 15 occur, the image transfer positions can be matched with the same period, so that the speed fluctuations between the image transfer positions. Therefore, it is possible to eliminate the color misregistration by eliminating the image transfer position misalignment.
[0040]
Since the embodiment of the present invention has the above-described configuration, the driving is performed on a flat surface portion having no curvature in the intermediate transfer belt 2, so that the support rollers 2 </ b> A and 2 </ b> B are provided even if the intermediate transfer belt 2 has a different thickness. Unlike the case of driving at 2C, there is no difference in peripheral speed on the roller peripheral surface. As a result, it is possible to prevent the speed fluctuations from matching between the image transfer positions, thereby preventing the occurrence of color shift due to the shift of the image transfer position.
[0041]
On the other hand, regarding the speed fluctuation of the intermediate transfer belt 2 at each image transfer position, the circumferential length of the driving roller 14 of the intermediate transfer belt 2 is the condition described in (1), and therefore exists in the intermediate transfer belt 2. If the period of speed fluctuation caused by the difference in thickness is the same at each image transfer position, the speed deviation at each image transfer position can be eliminated. As a result, the speed change at the time when the intermediate transfer belt 2 reaches each image transfer position can be matched between the image transfer positions, and the image transfer position can be prevented from shifting. It is possible to eliminate the color misregistration caused by.
[0042]
Regarding the speed fluctuation of the intermediate transfer belt 2, the diameter of the counter roller 15 that sandwiches and drives the intermediate transfer belt 2 in cooperation with the driving roller 14 is set as the condition described in (2). Even when a typical speed fluctuation occurs, each image transfer position can be matched by the same cycle, so that there is no speed fluctuation deviation between each image transfer position, and the image transfer position deviation caused by this can be avoided. The color shift can be released without it.
[0043]
【The invention's effect】
According to the first aspect of the present invention, the diameter of the counter roller is set to an integral number (1 / n) of the circumference of the drive roller, and the diameter of the drive roller is also an integer of the circumference of the drive roller. Since it is set to a fraction (1 / n), it is possible to prevent a change in the nip state constituted by the driving roller and the opposing roller, and even when a periodic speed fluctuation of the roller occurs between the rollers, Since the image transfer positions can be made to coincide with each other at the same cycle, there is no shift in speed fluctuation between the image transfer positions, and it is possible to eliminate the color shift by eliminating the shift of the image transfer position due to this. Become.
[0044]
According to the second aspect of the present invention, the drive source is disposed at the upstream side of the transfer position in the belt movement direction, so that there is no speed difference before the transfer on the belt. It is possible to prevent the occurrence of color misregistration by preventing the image transfer position from shifting .
[0045]
According to the third aspect of the present invention, since the change in the moving speed of the belt when using the belt is matched at each image transfer position, the shift of the image transfer position due to the difference in the speed fluctuation at each image transfer position. It is possible to obtain an image without color misregistration .
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus including a transfer device according to an embodiment of the present invention.
FIG. 2 is a partially enlarged view for explaining a configuration of a transfer apparatus according to an embodiment of the present invention.
FIG. 3 is a schematic diagram showing an example of a multicolor image forming apparatus equipped with a transfer device using a belt.
FIG. 4 is a schematic diagram showing another example of a multicolor image forming apparatus equipped with a transfer device using a belt.
FIG. 5 is a schematic diagram showing a configuration of an apparatus using a belt.
FIG. 6 is a schematic diagram for explaining a peripheral speed according to a dimensional relationship between a thickness of a belt and a roller around which the belt is wound.
7 is a schematic diagram for explaining the peripheral speed when the thickness of the belt shown in FIG. 6 is different from the case of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser printer 1A which is an example of image forming apparatus Image forming part 2 Intermediate transfer belt 2A located in primary transfer part 2A Intermediate transfer belt drive roller 2B Intermediate transfer belt driven roller 3 Photoconductor 9 2 which is a latent image carrier Next transfer device 9A Charging roller 14 for secondary transfer Drive roller 15 as one component of belt drive source Opposing roller 16 as another component of belt drive source Drive motor P1 Each latent image carrier and intermediate transfer belt Between image transfer positions facing each other

Claims (3)

A transfer device having a configuration in which images of different colors subjected to visible image processing on a plurality of latent image carriers are sequentially transferred to a transfer member using a single belt that passes through the position of each latent image carrier. In
The belt is wound around at least one pair of rollers, and is driven by a driving source different from the rollers , and the driving source is capable of being driven by a driving roller and a driving roller that are opposed to each other with a flat portion having no curvature in the belt. It is equipped with a counter roller that forms a pressure means,
The diameter of the counter roller is set to approximately 1 / nth of the diameter of the driving roller (1 / n), and the circumferential length of the driving roller is an integer of the arrangement interval of the latent image carriers. 1 (1 / n) is set . The transfer apparatus according to claim 1, wherein
The transfer apparatus is characterized in that the arrangement position of the driving source is set on the upstream side in the moving direction of the belt with respect to the transfer position of the image on the flat portion of the belt . An image forming apparatus using the transfer device according to claim 1 .

Images