JP2004138815A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having no deterioration of an image without producing any color shift and jitter by preventing the change of a nip pressure when a recording medium advances into a nip while suppressing the complexing and upsizing the apparatus. <P>SOLUTION: The image forming apparatus has a transfer means 1 arranged in opposition to an image carrier 101 and for transferring a toner image on the image carrier 101 on the recording medium in an opposite region 107 with the image carrier 101. The transfer means 1 is loaded by a gravity toward the image carrier 101. Thus, a change in the nip pressure can be prevented when the recording medium advances into the nip, the color shift and the jitter are not produced to have no image deterioration, and the image of high image quality can be formed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, and the like, which includes a transfer unit that transfers a toner image on an image carrier to a recording medium.
[0002]
[Prior art]
As for image forming apparatuses such as copying machines, printers, and facsimile machines, color electrophotographic apparatuses such as color copying machines and color printers, that is, image forming apparatuses that perform color image formation, have been increasing in accordance with market requirements. The image forming apparatus includes, for example, a photoreceptor as an image carrier, and transfers a toner image on the photoreceptor to a recording medium at a nip, which is a region facing the photoreceptor, by a transfer unit disposed to face the photoreceptor. However, the color image forming apparatus is provided with a plurality of color developing devices around one photoreceptor, and the toners of the respective colors are adhered by the developing devices to form a color image on the photoreceptor. A so-called one-drum type in which a synthetic toner image is formed and the toner image is transferred and a color image is recorded on a sheet-shaped recording medium, and a plurality of photoconductors arranged side by side are provided with respective developing devices. There is a so-called tandem type in which a single color toner image is formed on a photoreceptor, and the single color toner images are sequentially transferred to record a composite color image on a recording medium.
[0003]
Comparing the one-drum type and the tandem type, the former has the advantage of relatively small size and reduced cost because it has only one photoreceptor, There is a problem that it is difficult to increase the speed of image formation because a full-color image is formed by repeating image formation twice, and the latter, in contrast to the former, is problematic in that the size increases and the cost increases. There is an advantage that the speed of formation is easy.
[0004]
In both the one-drum type and tandem type image forming apparatuses, the demand for image quality has recently increased, and attention has been paid to color misregistration and jitter as one of the causes of image deterioration. The cause of the jitter is a change in the nip pressure caused by a change in the center distance of the nip portion, which occurs when the recording medium enters the nip. That is, when the transfer means applying the nip pressure moves, the applied load fluctuates, or the actual load fluctuates because the inclination in the direction in which the load is applied fluctuates. Since the running of the rotating body such as the transfer unit becomes uneven, color shift and jitter occur. In order to solve such a problem, Japanese Patent Application Laid-Open No. H11-163873 proposes a technology that includes a mechanism for positioning the rotating body and keeps the nip pressure constant.
[0005]
[Patent Document 1]
JP-A-11-024451
[Problems to be solved by the invention]
However, the technique described in [Patent Document 1] has a problem that the device becomes complicated and large in size due to the provision of such a positioning mechanism.
[0007]
The present invention focuses on the fact that a change in the nip pressure when the recording medium enters the nip causes image deterioration, and prevents a change in the nip pressure while suppressing the complexity and size of the apparatus, thereby preventing color change. It is an object of the present invention to provide an image forming apparatus in which no image degradation is caused without generation of displacement and jitter.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, there is provided a transfer means which is arranged to face an image carrier and transfers a toner image on the image carrier to a recording medium in a region facing the image carrier. In the image forming apparatus having the above structure, the transfer unit is loaded by gravity toward the image carrier.
[0009]
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the transfer unit is loaded toward the image carrier by the weight of the transfer unit itself.
[0010]
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, a weight is provided to load the transfer unit toward the image carrier by a difference between the weight of the transfer unit and the weight of the transfer unit. And
[0011]
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, a flexible connecting member for connecting the transfer means and the weight is provided, and the connecting member is engaged with the flexible member to bend the connecting member. And a bending point forming means for forming a bending point.
[0012]
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the bending point forming means is a pulley.
[0013]
According to a sixth aspect of the present invention, in the image forming apparatus according to the first to fifth aspects, the image forming apparatus is engaged with the transfer unit, and changes a displacement of the transfer unit in a portion where the image carrier and the transfer unit come into contact with each other. It is characterized by having a regulating member for regulating in a direction perpendicular to the tangential direction of the body.
[0014]
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, at least a portion of the regulating unit that engages with the transfer unit has lubricity.
[0015]
【Example】
FIG. 1 schematically shows an image forming apparatus to which the present invention is applied. The image forming apparatus may be any known one such as a copying machine, a facsimile, and a printer, but the image forming apparatus in this embodiment is a printer. The image forming apparatus of the present embodiment forms a color image.
[0016]
The image forming apparatus 100 has a higher heat capacity than plain paper generally used for copying and the like, 90K paper such as OHP sheets, cards, and postcards, thick paper having a basis weight of about 100 g / m ² or more, and envelopes. Any of the large so-called special sheets can be used as a sheet-shaped recording medium for forming an image. The size of the recording medium is generally a size conforming to a general standard such as A4 size or A3 size, but may be a size outside the standard.
[0017]
The image forming apparatus 100 is a tandem-type color image forming apparatus, and is a cylindrical rotating body that is driven to rotate in the direction of arrow A, and uses a photoconductor using an organic semiconductor (OPC) as an image carrier. A drum (hereinafter, referred to as “photoconductor”) 101, a charging device (not shown) for charging the photoconductor 101, and an exposure (not shown) for emitting a laser beam for forming a latent image on the charged photoconductor 101 and performing optical scanning. A developing device (not shown) that develops the latent image on the photoconductor 101 after exposure, and a recording medium that is disposed to face the photoconductor 101 and that obtains a toner image on the photoconductor 101 obtained by development by the developing device 104. A transfer device 105 having a transfer roller 1 which is a rotating body and a final transfer body, which is a rotating body as a transfer means for transferring onto a sheet as a material to be transferred, and cleans the surface of the photosensitive body 101 after the transfer. A cleaning device (not shown), a static eliminator for neutralizing the photoconductor 101 before charging by the charging device, a paper feed tray 102 on which paper is loaded, and a photoconductor 101 for transporting the paper loaded on the paper tray 102 A registration roller 109 which is conveyed at a predetermined timing to a transfer area 107 as a nip, which is a region where the photoconductor 101 and the transfer roller 1 are in contact with the transfer device 105 and which is in contact with the transfer roller 1. A fixing device 108 which is a fixing unit as a fixing unit for fixing the toner image onto the sheet on which the toner image has been transferred, and a discharge tray which is located outside the main body of the image forming apparatus 100 and on which the fixed sheet is stacked. 103.
[0018]
Since the image forming apparatus 100 is a tandem type image forming apparatus, an image forming system including the photoconductor 101, the charging device, the exposing device, the developing device, the transfer device 105, the cleaning device, and the charge removing device is, for example, cyan, For each of the colors magenta, yellow, and black, they are provided along the paper transport path 11 indicated by the broken line in FIG. 1, but only one of them is shown in FIG.
[0019]
As shown in FIG. 2, the photoreceptor 101 and the transfer roller 1 are driven to rotate in the A and B directions by a motor 2 and a motor 3, respectively. The direction B is a direction in which the photosensitive drum 101 moves in the same direction as the direction A at a position facing the photosensitive member 101. The toner image on the photoreceptor 101 is transferred and carried on a transfer area 107 formed by the photoreceptor 101 and the transfer roller 1 rotating in this manner. The fixing device 108 includes a heating roller 59 that is a fixing roller for transporting a sheet on which the toner is fixed, and a rotation of the heating roller 59 in the fixing unit 16 that is in contact with the heating roller 59 and that is in contact with the heating roller 59. It has a pressure roller 60 as a pressure member that rotates in the same direction G as the direction F.
[0020]
As shown in FIG. 3, the transfer roller 1 is loaded toward the photoconductor 101 by gravity, and the transfer pressure in the transfer area 107 is defined. That is, the transfer device 105 includes a wire 4 as a flexible connection member having one end connected to the shaft 6 of the transfer roller 1, and a weight connected to the other end of the wire 4 and connected to the transfer roller 1 by the wire 4. The transfer roller 1 is loaded toward the photosensitive member 101 due to the difference between the weight of the weight 5 and the weight of the transfer roller 1.
[0021]
The transfer device 105 also includes a pulley 8 rotatable at a fixed position, which is bending point forming means for engaging the wire 4 by winding the wire 4 and bending the wire 4 to form a bending point 7. And a restricting member 10 as a restricting member that engages with the shaft 6 to restrict the displacement of the transfer roller 1 in a direction D perpendicular to the tangential direction C of the photoconductor 101 in the transfer area 107 and to restrict the transfer. I have. The weight 5 is suspended vertically downward via the bending point 7.
[0022]
The spacing between the restraining members 10 is slightly larger than the diameter of the shaft 6 so that the shaft 6 slides smoothly, and is made of a polyamide resin (PA), a polyacetal resin (POM), an oil-impregnated resin material, or the like. The material is a resin having slidability. As described above, the entirety of the constraining member 10 may be made of a material having lubricity. It is only necessary that the portion that engages with the shaft 6 of the transfer roller 1 and slides with the shaft 6 has lubricity. Further, since the pulley 8 wraps the wire 4, the wire 4 has a very small influence of the friction caused by the bending point forming means when the wire 4 is displaced. This also applies to the pressing force of the transfer roller 1 against the photosensitive member 101. Does not occur, and the tracking performance is not impaired.
[0023]
The arrangement position of the pulley 8 and the restraining member 10 and the direction D in which the shaft 6 is restricted by the restraining member 10 are determined so that the shaft 6 comes into contact with and separates from the rotation center 9 of the photoconductor 101. As a result, the extension of the rotation center portion 9 always overlaps the extension direction of the wire 4 located between the pulley 8 and the shaft 6, and the transfer roller 1 starts moving when the paper starts passing through the transfer area 107. The sheet is displaced only in the direction approaching the rotation center 9 in the D direction, and is displaced only in the direction away from the rotation center 9 in the D direction when the paper finishes passing through the transfer area 107.
[0024]
Since the connection member has flexibility, a natural load can be applied to the transfer roller 1 regardless of the arrangement position of the transfer roller 1, the photosensitive member 101, and the like, without being restricted by the configuration. Assuming that there is no restraint member 10 in the scale, as shown in FIG. 4, the transfer roller 1 has a displacement component other than the D direction as shown by a broken line. However, it is displaced in the C direction and cannot be displaced only in the D direction when it is displaced due to the passage of a sheet.
[0025]
With such a configuration, the transfer device 105 loads the transfer roller 1 toward the photoreceptor 101 by gravity, so that even if a sheet enters the transfer area 107 and the transfer roller 1 is displaced in the D direction, Is performed smoothly, the transfer pressure in the transfer area 107, that is, the nip pressure is constant, the load applied to the sheet and the photosensitive member 101 does not fluctuate, color shift and jitter do not occur, and image deterioration is prevented.
[0026]
The number of the bending point forming means is not limited to one, but may be plural as shown in FIG. In the example shown in FIG. 5, two pulleys 8 are provided, and two bending points 7 are formed accordingly. By providing a plurality of bending points 7 in this manner, the degree of freedom in the configuration of the photoconductor 101 and the transfer device 105 is further improved. In this case, as in the above-described example shown in FIG. 3, the bending point forming means closest to the transfer roller 1 has a relationship between the arrangement position of the restricting member 10 and the restricting direction D of the shaft 6 by the restricting member 10. , And the shaft 6 is set in a direction in which the shaft 6 comes into contact with and separates from the rotation center 9 of the photoconductor 101.
[0027]
Also in this case, assuming that there is no restraint member 10 in the scale, as shown in FIG. 6, the transfer roller 1 has a displacement component other than the D direction as shown by a broken line, The transfer member 1 is displaced in the C direction, and cannot be displaced only in the D direction even when displaced by the passage of the sheet. The extension of the rotation center 9 always overlaps with the direction in which the wire 4 is positioned between the shaft 6 and the transfer roller 1. When the paper starts to pass through the transfer area 107, the transfer roller 1 9, the sheet is displaced only in a direction away from the rotation center portion 9 in the direction D when the sheet has finished passing through the transfer area 107.
[0028]
Since the image forming apparatus 100 is configured as described above, the power of the image forming apparatus 100 is turned on by a predetermined operation by the operator, or after the image forming apparatus 100 shifts from the standby state to the operating state, the image forming apparatus 100 starts image formation. When a well-known operation is performed, in the image forming system of each color, the photoconductor 101 uniformly charged by the charging process by the charging device is irradiated according to data input from the outside by rotating in the direction of arrow A. After the latent image formation in the exposure process by the laser beam, the development process performed by development by the development device, the transfer process by the transfer device, the cleaning process by the cleaning device, and the charge removal process by the charge removal device, the process proceeds to the charging process again.
[0029]
Such a transfer step is performed in synchronization with the timing of conveyance of the sheet conveyed along the conveyance path 11, and in the course of conveyance along the conveyance path 11, the toner image is transferred onto the sheet by the superimposition transfer in all the transfer steps. Then, the image is fixed on the sheet by the fixing process in the fixing device 108. The sheet on which the toner image is fixed and the color image is formed is discharged out of the image forming apparatus 101. In such an image forming step, the transfer step is performed without causing image deterioration because the transfer roller 1 is weighted by the gravity to the photoreceptor 101, whereby the image is formed favorably.
[0030]
As described above, the image forming apparatus to which the present invention is applied has been described. However, the transfer unit is disposed above the image carrier, and only the weight of the transfer unit itself is used to load the image carrier by gravity. Is also good. The transfer means is not limited to the transfer roller, and may use a transfer belt. In this case, a connecting member is connected to a shaft of the roller around which the transfer belt is wound, and the shaft is restrained by a regulating member. This axis can be replaced with the axis 6 described above. The image carrier may be in the form of a belt instead of a drum. In this case, the belt comes into contact with the belt of the transfer unit in a direction perpendicular to the direction in which the belt abuts the transfer unit in the direction in which the belt is stretched or moved. A restricting member or the like can be configured to displace the portion.
[0031]
Although the tandem type color image forming apparatus has been described, the present invention can be applied to a one-drum type color image forming apparatus. In this case, the color image forming apparatus is arranged to face one image carrier. Each transfer means for transferring a toner image of each color is loaded by gravity toward the image carrier. In this case, a large number of components are arranged around the image carrier. However, by using a connecting member, there is a high degree of freedom in the arrangement of the transfer unit, the bending point forming unit, and the like, which causes a problem in the arrangement of the transfer device. Does not occur. When a plurality of bending point forming means are provided, the number is not limited to two and may be three or more.
[0032]
【The invention's effect】
The present invention is directed to an image forming apparatus including a transfer unit that is disposed to face an image carrier and transfers a toner image on the image carrier to a recording medium in a region facing the image carrier. Since a load is applied to the image carrier by gravity, it is possible to prevent a change in the nip pressure when the recording medium enters the nip, and to form a high-image-quality image without color shift, jitter, and image deterioration. An image forming apparatus capable of performing the above can be provided.
[0033]
If the transfer means is loaded toward the image carrier by the weight of the transfer means itself, the load is applied only by the weight of the transfer means itself, so the nip when the recording medium enters the nip with a simple configuration Provided is an image forming apparatus capable of preventing a change in pressure, suppressing an increase in complexity and size of the apparatus, and performing high-quality image formation without causing color shift, jitter, and image deterioration. can do.
[0034]
By providing a weight for loading the transfer means toward the image carrier due to the difference between the weight of the transfer means and the weight of the transfer means, the nip pressure when the recording medium enters the nip can be relatively easily configured. The present invention provides an image forming apparatus capable of preventing a change in image quality, suppressing an increase in complexity and size of the apparatus, and performing high-quality image formation without causing color misregistration, jitter, and image deterioration. be able to.
[0035]
A flexible connection member for connecting the transfer means and the weight, and a bending point forming means for engaging the connection member and bending the connection member to form a bending point, the transfer means is provided. Even when the transfer unit is not positioned above the image carrier, the transfer unit can be weighted toward the image carrier by gravity, and an image forming apparatus having a high degree of freedom in design can be provided.
[0036]
If the bending point forming means is a pulley, the sliding friction with the connecting means is reduced, and the weight is applied by gravity toward the image carrier without impairing the movement of the transfer means when the recording medium enters the facing area. The present invention can provide an image forming apparatus capable of forming an image with high image quality while preventing image deterioration.
[0037]
If a regulating member which engages with the transfer means and regulates the displacement of the transfer means in a direction perpendicular to the tangential direction of the image carrier at a portion where the image carrier and the transfer means abut is provided, The transfer unit can be one-dimensionally displaced only in a direction perpendicular to a tangential direction of the image carrier at a portion where the carrier and the transfer unit abut, and fluctuation of the fixing pressure due to a change in the load direction can be reduced. It is possible to provide an image forming apparatus capable of preventing the formation of an image with high image quality.
[0038]
As long as at least a portion of the regulating means that engages with the transfer means has lubricity, it is possible to apply gravity to the image carrier without impairing the movement of the transfer means when the recording medium enters the opposed area. Accordingly, it is possible to provide an image forming apparatus capable of forming an image with high image quality while preventing image deterioration.
[Brief description of the drawings]
FIG. 1 is a side view schematically showing an image forming apparatus to which the present invention is applied.
FIG. 2 is a perspective view showing how each of an image carrier and a transfer unit shown in FIG. 1 is driven.
FIG. 3 is a side view illustrating a configuration of a transfer device that loads the transfer unit illustrated in FIG. 1 toward an image carrier by gravity.
FIG. 4 is a side view showing a case where the transfer device shown in FIG. 3 is not provided with a regulating member.
FIG. 5 is a side view illustrating another example of the configuration of the transfer device that loads the transfer unit toward the image bearing member by gravity.
FIG. 6 is a side view showing a case where the transfer device shown in FIG. 5 is not provided with a regulating member.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Transfer means 4 Connection member 5 Weight 7 Bending point 8 Bending point forming means, pulley 10 Regulation member 100 Image forming apparatus 101 Image carrier 107 Image carrier 107 Opposite area between image carrier and transfer means

Claims (7)

An image forming apparatus having a transfer unit that transfers a toner image on the image carrier to a recording medium in a region facing the image carrier and facing the image carrier,
An image forming apparatus, wherein the transfer unit is loaded by gravity toward the image carrier. 2. The image forming apparatus according to claim 1, wherein the transfer unit is weighted toward the image carrier by the weight of the transfer unit itself. 2. The image forming apparatus according to claim 1, further comprising a weight for applying a load to the image bearing member by the difference between the weight of the transfer unit and the weight of the transfer unit. 4. The image forming apparatus according to claim 3, wherein a flexible connecting member that connects the transfer unit and the weight is formed, and a bending point is formed by engaging the connecting member and bending the connecting member to form a bending point. And an image forming apparatus. 5. The image forming apparatus according to claim 4, wherein said bending point forming means is a pulley. 6. The image forming apparatus according to claim 1, wherein said transfer means is engaged with said transfer means, and a displacement of said transfer means is perpendicular to a tangential direction of said image carrier at a portion where said transfer member contacts said transfer means. An image forming apparatus, comprising: a regulating member that regulates an image. 7. An image forming apparatus according to claim 6, wherein at least a portion of said regulating means which engages with said transfer means has lubricity.

Images