JP4176510B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, and a facsimile.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a color image forming apparatus having a quadruple tandem configuration transfers a transfer sheet by a transfer belt, and arranges a bias applying member at a position opposed to a plurality of photosensitive drums via the transfer belt. By applying a transfer bias to the toner image, each color toner image on the plurality of photosensitive drums is sequentially superimposed on the transfer paper on the transfer belt and transferred to form a color image. There is known a technique in which a single color toner image on a drum is transferred onto a transfer paper on a transfer belt to form a single color image.
[0003]
In this four-tandem color image forming apparatus, the transfer paper conveyance speed is generally almost the same as the surface speed of the transfer belt in order to adsorb and convey the transfer paper to the transfer belt. Regarding the surface speed of the transfer belt and the surface speed of the photosensitive drum, when these speeds are the same, the toner image is transferred from the photosensitive drum to the transfer paper on the transfer belt only by electrostatic force. If there is a speed difference between the surface speed of the transfer belt and the surface speed of the photosensitive drum, the transfer belt is removed from the photosensitive drum by the mechanical peeling force in addition to the electrostatic force. Since the toner image is transferred to the upper transfer paper, it is possible to prevent deterioration in image quality due to poor transfer.
[0004]
More specifically, when the surface speed of the transfer belt is different from the surface speed of the photosensitive drum, particularly good transferability is obtained when a color image is formed by superposing two or more toner images. Is obtained. When there is no superposition of toner images such as when forming a monochromatic image, the toner layer can be relatively easily held on the transfer paper surface, and a transfer property of a certain level or more can be easily secured.
[0005]
However, when a color image is formed by superimposing two or more color toner images, the toner image on the photosensitive drum is transferred from the toner layer already transferred onto the transfer paper to the part where the two or more color toner images are superimposed. Since the toner is newly transferred, the transferability of the newly transferred toner is deteriorated. For this reason, a method of giving a speed difference between the surface speed of the transfer belt and the surface speed of the photosensitive drum is effective.
[0006]
In this way, in order to improve transferability when two or more color toner images are transferred in a superimposed manner, the image forming apparatus is set so as to have a speed difference between the surface of the transfer belt and the surface of the photosensitive drum. In the image forming apparatus set in this way, when there are two or more different sheet passing speeds, they are expressed by (the surface speed of the transfer belt / the surface speed of the photoreceptor) regardless of the sheet passing speed. The “speed ratio between the transfer belt and the photosensitive drum” is generally designed to be kept constant.
Specifically, a stepping motor is generally used as a motor for driving the photosensitive member and the transfer belt. In this case, a desired driving speed can be obtained only by changing the number of pulses applied to the motor. In other words, when the paper feeding speed is half, the number of pulses given to the drive motor is usually designed to be half, so even if the paper feeding speed is changed, the "speed ratio between the transfer belt and the photosensitive drum" Is constant.
[0007]
For example, in a color image forming apparatus having a quadruple tandem configuration, there is Patent Document 1 in which the speed of the transfer belt is 0.1 to 1% higher than the speed of the photosensitive member.
When there is a speed difference between the photosensitive drum and the transfer belt or the paper on the transfer belt, the transfer belt or the paper on the transfer belt is separated into a loose side and a tension side due to the relative speed difference. On the loose side, the transfer belt tension is weakened, so that the transfer paper conveyance speed in the vicinity of the transfer nip becomes unstable, causing a color shift in the sub-scanning direction. It has been experimentally found that the amount of looseness that affects the color misregistration depends on the relative speed difference, not the speed ratio between the photosensitive drum and the transfer belt. That is, in the conventional apparatus, in the mode in which the sheet passing speed is different, the rotation speed of the motor is simply reduced according to the change ratio of the sheet passing speed, so that the speed ratio is always set to be constant. .
[0008]
More specifically, for example, in an image forming apparatus having two or more sheet passing speeds, the relative speed difference between the photosensitive member and the transfer belt when the sheet passing speed is 200 mm / sec is set to 1 mm / sec. In the case where both the scanning color misregistration amount and the transfer property are secured, the relative speed difference between the photosensitive member and the transfer belt is set to 0.5 mm / sec at a paper passing speed of 100 mm / sec. It was.
However, since the sub-scanning color misregistration has a correlation with the relative speed difference, even if the speed difference is set until the relative speed difference becomes 1 mm / sec, the sub-scanning color misregistration does not cause a problem.
Also, the transferability improves as the relative speed difference increases, so under the conventional setting conditions, the setting condition for the speed difference between the photoconductor and the transfer belt when the sheet passing speed is slow is not the optimum condition. It was a disadvantageous condition for sex.
[0009]
[Patent Document 1]
Japanese Patent No. 2743359 gazette
[Problems to be solved by the invention]
In view of the above-described problems, the present invention provides an image forming apparatus configured to ensure setting conditions for reducing color misregistration in the sub-scanning direction and improve transferability in a mode in which the transfer paper conveyance speed is low. Let it be an issue.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has two or more different transfer paper conveyance speeds, and a plurality of first image carriers and images on the plurality of first image carriers are converted into second images. In a tandem type image forming apparatus having a transfer means for transferring to an image carrier and having a speed difference between the first image carrier and the second image carrier, before and after changing the transfer paper conveyance speed The difference in speed between the second image carrier and the first image carrier expressed by ((surface velocity of the second image carrier) − (surface velocity of the first image carrier)) The surface speed of the first image carrier and the surface speed of the second image carrier are set so that “the same ” is the same .
[0012]
A first aspect of the present invention is transferred in the image forming apparatus of the present invention, the pre-Symbol first image bearing member is a photosensitive drum, said second image bearing member to be conveyed is attracted to the transfer belt An image forming apparatus characterized in that it is paper.
A second aspect of the present invention is an image forming apparatus of the present invention, the pre-Symbol first image bearing member is a photosensitive drum, and said second image bearing member is an intermediate transfer belt An image forming apparatus.
[0013]
A third aspect of the present invention, the Te image forming apparatus odor according to any one, is the "second expressed in (the surface speed of the second image bearing member surface speed / first image bearing member) Ru der image forming apparatus characterized by the image bearing member and the speed ratio of the first image bearing member "is set in the range of less than 0.98 0.995.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment in which the present invention is applied to an electrophotographic direct color transfer color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus will be described with reference to FIGS.
FIG. 1 is a schematic configuration diagram of a laser printer according to the present embodiment. In this laser printer, four toner image forming units 1Y, 1M, 1C, and 1K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K) are transferred. They are arranged in order from the upstream side in the moving direction of the paper 100. The transfer paper 100 moves along the arrow A in the figure in the direction in which the belt 60 travels. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes photosensitive drums 11Y, 11M, 11C, and 11K as image carriers and a developing unit. In addition, the arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel and arranged at a predetermined pitch in the transfer paper moving direction. .
[0015]
In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer carries the optical writing unit 2, the paper feed cassettes 3 and 4, the registration roller pair 5, and the transfer paper 100, and each toner image forming unit. A transfer unit 6 as a belt driving device having a transfer conveyance belt 60 as a transfer conveyance member that conveys the sheet so as to pass through the transfer position, a belt fixing type fixing unit 7, a paper discharge tray 8, and the like. In addition, a manual feed tray MF and a toner supply container TC are provided, and a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line.
The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning the laser beam based on image data. To do.
[0016]
FIG. 2 is an enlarged view showing a schematic configuration of the transfer unit 6. The transfer conveyance belt 60 used in the transfer unit 6 is a high-resistance endless single-layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm, and the material thereof is PVDF (polyvinylidene fluoride). The transfer conveyance belt 60 is wound around support rollers 61 to 68 so as to pass through the transfer positions that are in contact with and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units.
Among these support rollers, the entrance roller 61 on the upstream side in the transfer sheet moving direction is disposed on the outer peripheral surface of the transfer conveyance belt 60 so that the electrostatic adsorption roller 80 to which a predetermined voltage is applied from the power source 65a is opposed. Yes. The transfer paper 100 that has passed between the two rollers 61 and 65 is electrostatically attracted onto the transfer conveyance belt 60.
A roller 63 is a drive roller that frictionally drives the transfer conveyance belt 60, and is connected to a drive source (not shown) and rotates in the direction of the arrow.
[0017]
As a transfer electric field forming means for forming a transfer electric field at each transfer position, transfer bias applying members 67Y, 67M, 67C, and 67K are provided at positions facing the photosensitive drum so as to be in contact with the back surface of the transfer conveyance belt 60. ing. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller core from each transfer bias power source 9Y, 9M, 9C, 9K. Due to the action of the applied transfer bias, a transfer charge is applied to the transfer conveyance belt 60, and a transfer electric field having a predetermined strength is formed between the transfer conveyance belt 60 and the surface of the photosensitive drum at each transfer position. In addition, a backup roller 68 is provided to keep the contact between the transfer paper and the photoconductor in the area where the transfer is performed, and to obtain the best transfer nip.
[0018]
The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated around a rotation shaft 94. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow.
The entrance roller 61 and the suction roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state shown in FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of these brackets 90, 93, the bias applying members 67Y, 67M, 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photoreceptors 11Y, 11M, 11C, and the entrance roller 61 and the suction roller 80 also moves downward. It is possible to avoid contact between the photoconductors 11Y, 11M, and 11C and the transfer conveyance belt 60 when forming a black-only image.
[0019]
On the other hand, the transfer bias applying member 67K and the backup roller 68 adjacent to the transfer bias applying member 67K are rotatably supported by the outlet bracket 98, and are rotatable about a shaft 99 coaxial with the outlet roller 62. When attaching / detaching the transfer unit 6 to / from the main body, the transfer unit 6K is rotated clockwise by operating a handle (not shown), and the transfer bias applying member 67K and the backup roller 68 adjacent thereto are moved from the black image forming photosensitive member 11K. They are separated.
A cleaning device 85 composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer conveyance belt 60 wound around the driving roller 63. The cleaning device 85 removes foreign matters such as toner adhering to the transfer conveyance belt 60.
[0020]
A roller 64 is provided downstream of the driving roller 63 in the traveling direction of the transfer conveyance belt 60 in a direction to push the outer peripheral surface of the transfer conveyance belt, and a winding angle around the drive roller 83 is ensured. A tension roller 65 that applies tension to the belt by a spring 69 that is a pressing member is provided in the loop of the transfer conveyance belt 60 further downstream from the roller 64.
The one-dot chain line in FIG. 1 shown above indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The transfer paper 100 delivered at a predetermined timing by the registration roller pair 5 is carried on the transfer conveyance belt 60, conveyed toward the toner image forming units 1Y, 1M, 1C, and 1K, and passes through the transfer nips. .
The toner images developed on the toner drums 11Y, 11M, 11C, and 11K of the toner image forming units 1Y, 1M, 1C, and 1K are superimposed on the transfer paper 100 at the transfer nips, respectively. It is transferred onto the transfer paper 100 under the action of pressure. By this superposition transfer, a full-color toner image is formed on the transfer paper 100.
[0021]
The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further discharged to prepare for the formation of the next electrostatic latent image.
On the other hand, the transfer paper 100 on which the full-color toner image is formed is fixed in the first paper discharge direction B or the second in accordance with the rotation posture of the switching guide G after the full-color toner image is fixed by the fixing unit 7. In the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward a post-processing device such as another sorter and binding device (not shown), or again through a switchback unit for double-sided printing. Carried to pair 5.
[0022]
(Detailed description of the present invention)
Hereinafter, the present invention will be described in detail with reference to FIGS.
FIG. 3 is a conceptual diagram of the transfer belt slack side tension measuring device. As shown in FIG. 3, an experimental system for measuring the belt tension at the downstream portion of the transfer nip of the transfer belt is assembled, and the relative speed difference is obtained by making the speed of the photosensitive drum variable. FIG. 4 shows the result of measuring the loose side tension with a speed difference between the photosensitive drum and the transfer belt. The tension on the loose side continues to decrease until the relative speed difference reaches a certain value. FIG. 4 shows that the larger the relative speed difference, the lower the tension at the downstream portion of the transfer nip, the more unstable the transfer belt is, and the disadvantageous setting for sub-scanning color misalignment. ing.
[0023]
FIG. 5A shows the relationship between the ratio of the surface speed of the photoconductor and the surface speed of the transfer belt and the amount of color misregistration in the sub-scanning direction in an image forming apparatus having two different sheet passing modes. FIG. 5B shows the relationship between the relative speed difference between the surface speed of the photosensitive member and the surface speed of the transfer belt and the amount of color misregistration in the sub-scanning direction in an image forming apparatus having two different sheet passing modes.
From FIGS. 5A and 5B, in the image forming apparatus having the sheet passing mode having two or more different transfer sheet conveying speeds, the relative speed difference is constant in order to make the sub-scanning color misregistration constant. It can be seen that it is desirable to satisfy the following conditions.
[0024]
In particular,
In an image forming apparatus having a sheet passing speed that is two transfer sheet conveying speeds of 200 mm / sec and 100 mm / sec,
A mode in which the transfer belt surface speed is set to 200 mm / sec, the photoconductor surface speed is set to 201 mm / sec, a transfer belt surface speed is set to 100 mm / sec, and a photoconductor surface speed is set to 101 mm / sec.
[0025]
As a result, the relative speed difference between the transfer belt or the sheet sucked and conveyed on the transfer belt and the surface speed of the photosensitive member becomes 1 mm / sec regardless of the transfer sheet conveying speed. This value is a level at which the sub-scanning color misregistration amount can be experimentally allowed from FIG. 5B, that is, if this relative speed difference is large, the transferability is improved, but the sub-scanning color misregistration deteriorates. It is necessary to be determined by the balance between the two.
In this embodiment, when the sheet passing speed is 200 mm / sec, “the surface speed of the second image carrier” expressed by “the surface speed of the second image carrier / the surface speed of the first image carrier”. The speed ratio between the surface speed of the first image carrier and the first image carrier is 200/201 = 0.993.
When the sheet passing speed is 100 mm / sec, “the surface speed of the second image carrier and the first image” expressed by “the surface speed of the second image carrier / the surface speed of the first image carrier”. The speed ratio with the surface speed of the carrier is 100/101 = 0.99.
[0026]
As described above, even when the speed ratio is changed by changing the sheet passing mode, it is desirable that the speed ratio is a set value of 0.98 or more and less than 0.995. If it is less than 0.995, transferability by speed ratio can be secured. If it is less than 0.98, the transferability is good, but the force to weaken the paper adsorption force between the transfer paper and the transfer belt becomes excessive, so the color misregistration in the sub-scanning direction deteriorates. For this reason, the speed ratio is desirably 0.98 or more and less than 0.995. This value has been obtained experimentally and may shift somewhat depending on the machine usage environment, paper type, and system.
[0027]
FIG. 6 shows the relationship between the speed ratio and the transfer rate. As for the relationship between the photosensitive member surface speed and the transfer belt surface speed, the transfer rate, which is transferability, improves as the speed ratio increases as shown in FIG. 6, but as shown in FIG. The amount of deviation gets worse. Therefore, it is desired to be determined by a balance between transferability and sub-scanning color misregistration amount. However, as shown in FIG. 5B, even if the relative speed difference especially when the sheet passing speed is low and the relative speed difference when the sheet passing speed is high are substantially constant, the color deviation of the sub-scanning does not deteriorate. There was found. Therefore, when the sheet passing speed is low, it is possible to set the transferability under favorable conditions as compared with the control in which the speed ratio is constant as in the conventional setting.
【The invention's effect】
As described above, according to the present invention, in an image forming apparatus having two or more different transfer paper conveyance speeds, regardless of the direct transfer method or the intermediate transfer method, sub-scanning color misregistration is performed according to each transfer paper conveyance speed. Reduction can be achieved, and an image forming apparatus with improved transferability can be provided. In addition, the variation in speed due to the dimensional tolerance of parts generated under actual use conditions is absorbed by setting the speed ratio range between the surface speed of the first image carrier and the surface speed of the second image carrier. It becomes possible to do.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a color laser printer according to an embodiment.
FIG. 2 is an enlarged view of a schematic configuration of a transfer unit.
FIG. 3 is a conceptual diagram of a transfer belt slack side tension measuring apparatus.
FIG. 4 shows the relationship between the speed difference between the surface speed of the transfer belt and the surface speed of the photoreceptor and the loose side tension of the transfer belt.
FIG. 5 shows a relationship between a speed ratio and a speed difference between a surface speed of a transfer belt and a surface speed of a photosensitive member and a sub-scanning color misregistration amount in different paper passing modes.
FIG. 6 shows the relationship between the speed ratio between the surface speed of the transfer belt and the surface speed of the photosensitive member and the transfer rate when two or more toner images are transferred in an overlapping manner.
[Explanation of symbols]
1Y, 1M, 1C, 1K Toner image forming unit 2 Optical writing unit 3, 4 Paper feed cassette 5 Registration roller pair 6 Transfer unit 60 Transfer conveyance belts 61-68 Support rollers 67Y, 67M, 67C, 67K Transfer bias applying member 7 Fixing Unit 8 Paper discharge tray 9Y, 9M, 9C, 9K Transfer bias power supply 11Y, 11M, 11C, 11K Photosensitive drum 80 Electrostatic adsorption roller 80a Power supply 85 Cleaning device 90 Entrance roller bracket 91 Shaft 92 Pin 93 Swing bracket 94 Rotation Shaft 95 Hole 96 Cam 97 Cam shaft 98 Exit bracket 99 Shaft 100 Transfer paper A Belt running direction B First paper discharge direction C Second paper discharge direction G Switching guide MF Manual feed tray TC Toner supply container

Claims (4)

Two or more different transfer paper conveyance speeds, comprising a plurality of first image carriers, and transfer means for transferring images on the plurality of first image carriers to a second image carrier, In a tandem type image forming apparatus having a speed difference between a first image carrier and a second image carrier,
Before and after the transfer paper conveyance speed is changed, ((surface speed of the second image carrier) − (surface speed of the first image carrier)) An image forming apparatus, wherein the surface speed of the first image carrier and the surface speed of the second image carrier are set so that the “speed difference with the first image carrier” is the same. The image forming apparatus according to claim 1.
Before SL first image bearing member is a photosensitive drum, an image forming apparatus, wherein the second image bearing member is a transfer sheet being conveyed is attracted to the transfer belt. The image forming apparatus according to claim 1.
Before Symbol first image bearing member is a photosensitive drum, an image forming apparatus, wherein the second image bearing member is an intermediate transfer belt. The image forming apparatus according to any one of claims 1 to 3 ,
The “speed ratio between the second image carrier and the first image carrier” expressed by (surface velocity of the second image carrier / surface velocity of the first image carrier) is 0.98 or more and 0 An image forming apparatus set in a range of less than .995 .

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