JP4731962B2 - Transfer device, image forming device - Google Patents

Description

  The present invention relates to a transfer device that transfers and conveys transfer paper on a transfer and conveyance belt, and an image forming apparatus including the transfer device.

Conventionally, in a tandem color image forming apparatus, an endless belt that travels while supporting transfer paper is used in a direct transfer system, and an endless belt that receives and carries an image from a photoreceptor in an intermediate transfer system. It is known to employ (see, for example, Patent Documents 1 to 3).
Representative methods of color image formation include a direct transfer method in which toner images of different colors formed on a plurality of photoconductors are transferred while being superimposed directly on a transfer sheet, and toners of different colors formed on a plurality of photoconductors. There is an intermediate transfer method in which an image is transferred while being superimposed on an intermediate transfer member, and then transferred onto a transfer sheet at once.
Since a plurality of photoconductors are arranged side by side facing the transfer paper or intermediate transfer body, this is called a tandem method, and yellow (Y), magenta (M), cyan (C), and black (K) for each photoconductor. For each color, an electrophotographic process such as formation and development of an electrostatic latent image is performed, and the image is transferred onto a running transfer sheet in the direct transfer method, or onto a running intermediate transfer member in the intermediate transfer method.
In the tandem color image forming apparatus using each of these methods, the direct transfer method receives an endless belt that runs while supporting transfer paper, and the intermediate transfer method receives an image from a photoconductor. Generally, an endless belt to be carried is employed. Then, an image forming unit including four photoconductors is installed side by side on one running side of the belt.
In the tandem direct transfer system, it is very important that the transfer paper is sufficiently adsorbed on the belt. For this reason, the prior art also has an object of how to sufficiently attract the transfer paper to the belt.
For this reason, Patent Document 1 discloses a technique that can maintain a sufficient adsorbing force until the recording material adsorbed and conveyed by the transfer belt or the transfer drum reaches the adsorbing unit downstream.
Patent Document 2 discloses a technique for preventing color misregistration of paper conveyance by a transfer belt while reducing transfer voltage and improving safety.
Furthermore, Patent Document 3 discloses a technique for sufficiently adsorbing paper so that it can be used for vertical conveyance.
Patent Document 4 discloses a technique for applying a weak suction bias to the most advanced region of the conveyed paper.
JP 2001-106375 A Japanese Patent Laid-Open No. 07-160127 JP 11-084883 A Japanese Patent Laid-Open No. 09-222801

The technique disclosed in Patent Document 1 is a general method of using a suction roller. By always providing the necessary and sufficient suction force to the entire sheet, it is possible to stabilize the conveyance and prevent color misregistration. However, this technology is effective when the transfer belt is always uniform and smooth, and when the transfer paper follows the distortion of the transfer belt itself, this sufficient adsorption force is rather It becomes a cause.
The techniques of Patent Document 2 and Patent Document 3 also focus on the point that no problem occurs due to sufficient adsorption as in the above, but the transfer paper follows the distortion of the transfer belt itself. In fact, this sufficient attracting force causes an abnormal image.
Accordingly, an object of the present invention is to reduce the distortion of the transfer paper that is strongly stuck on the transfer conveyance belt by the electric charge applied from the suction roller in consideration of the above situation, that is, the distortion of the transfer conveyance belt itself. Another object of the present invention is to provide a transfer device and an image forming apparatus that reduce the relationship between the transfer sheet and the transfer paper by the suction level.

In order to achieve the above-mentioned object, an invention according to claim 1 is directed to an endless transfer / conveying belt that is driven to rotate around a plurality of rollers and carries the transferred transfer paper, and this transfer / conveying belt. A plurality of biases to which a transfer bias is applied so as to be in contact with the back surface of the transfer / conveying belt, respectively, facing the plurality of image carriers that are in contact with the outer peripheral surface of the belt at a predetermined interval in the transfer paper conveying direction. A plurality of image bearing members and a plurality of bias rollers, and transferring each toner image on the plurality of image bearing members on a transfer sheet on the transfer conveyance belt at a nip portion between the plurality of image bearing members and the plurality of bias rollers. in the apparatus, a transfer on the transfer conveyor belt is arranged on the outer peripheral surface of one roller opposite to the transfer conveyor belt of the plurality of rollers at the transfer sheet conveyance direction upstream of the transfer conveyor belt Electric charges are provided to comprise an electrostatic attraction roller for attracting the transfer sheet to the transfer conveyor belt, a bias control means for controlling the bias level applied to the electrostatic attraction roller, and said bias control means, wherein During the period in which the electrostatic attraction roller is in contact with the transfer paper, the bias level of the electrostatic attraction roller when the electrostatic attraction roller is in contact with the center of the transfer paper is determined. Control is performed so that the level is lower than the normal level of the electrostatic attraction roller when contacting the front end and the rear end.
According to a second aspect of the present invention, there is provided the transfer apparatus according to the first aspect, wherein the bias control means continuously varies the bias level supplied to the electrostatic attraction roller.
According to a third aspect of the present invention, there is provided the transfer device according to the first or second aspect, wherein the bias control means has a current applied to the electrostatic attraction roller as a bias.
According to a fourth aspect of the present invention, the bias control means includes a bias control table that changes the bias level according to the width of the transfer paper. Features the transfer apparatus described.
According to a fifth aspect of the present invention, there is provided an image forming apparatus including the transfer device according to any one of the first to fourth aspects.

According to the present invention, during the period in which the electrostatic attraction roller is in contact with the transfer paper , the bias level of the electrostatic attraction roller when the electrostatic attraction roller is in contact with the transfer paper center is set to the electrostatic level. By controlling the suction roller so that it is lower than the normal level of the electrostatic suction roller when contacting the leading edge and trailing edge of the transfer paper, distortion of the transfer paper on the transfer conveyance belt is reduced. Therefore, the transfer paper conveying operation at the transfer nip is stable, and abnormal images such as streaks due to transfer unevenness can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
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 showing an embodiment of a laser printer according to the present invention. FIG. 2 is an enlarged view showing a schematic configuration of the transfer unit of FIG. 1 and 2, the laser printer includes four toner image forming units 1Y, 1M, and 1M for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). 1C, 1K.
These toner image forming portions 1Y, 1M, 1C, and 1K (hereinafter, the suffixes Y, M, C, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively) are transferred. Arranged in order from the upstream side in the moving direction of the paper 30 (the direction in which a transfer conveyance belt 8 described later travels along the arrow A in the figure).
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. The toner image forming units 1Y, 1M, 1C, and 1K are arranged so that the rotation axes of the photosensitive drums 11Y, 11M, 11C, and 11K are parallel to each other and at a predetermined pitch in the transfer sheet moving direction. It is set to arrange.
The laser printer according to the present embodiment carries the toner image forming units 1Y, 1M, 1C, and 1K, the optical writing unit 2, the paper feed cassettes 3 and 4, the registration roller pair 5, and the transfer paper 30, and each toner. A transfer unit 6 having a belt driving device having a transfer conveyance belt 8 as a transfer conveyance member that conveys the image forming unit so as to pass through a transfer position, a belt fixing type fixing unit 7, a paper discharge tray 34, and the like are provided. .
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 the image data. To do.

The transfer conveyance belt 8 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 conveyor belt 8 passes through the transfer rollers 10, 12, 13, and 13 K so as to pass through the transfer positions that are in contact with and opposed to the photosensitive drums 11 Y, 11 M, 11 C, and 11 K of the toner image forming units 1 Y, 1 M, 1 C, and 1 K. 17 and 31.
Among these support rollers 10, 12, 13, 16, 17, 31, the transfer conveyance belt is arranged so that the electrostatic attraction roller 18 faces the entrance roller 31 on the upstream entrance roller 31 in the transfer sheet moving direction. 8 is arranged on the outer peripheral surface.
A required bias voltage or bias current is applied to the electrostatic attraction roller 18 from the bias control means 18b. A predetermined voltage is supplied from the power source 18a to the bias control means 18b.
The bias control means 18b has a bias control table (not shown) that changes the bias level according to the width of the transfer paper, and the bias level corresponding to the bias control table is statically controlled by an instruction from a controller (not shown). The voltage is applied to the electroadsorption roller 18.
As described above, in the laser printer of this embodiment, the bias control unit 18b makes the bias condition to be applied to the electrostatic attraction roller 18 appropriate so that the transfer that is hardly affected by the distortion of the transfer conveyance belt itself. It is characterized in that the method is realized. Details thereof will be described later.

The transfer paper 30 (see FIG. 1) that has passed between the electrostatic attraction roller 18 and the entrance roller 31 is electrostatically adsorbed on the transfer conveyance belt 8. The support roller 12 is a drive roller that frictionally drives the transfer conveyance belt 8, and is connected to a drive source (not shown) so as to rotate in the arrow direction.
As a transfer electric field forming means for forming a transfer electric field at each transfer position, a transfer bias applying member 15Y, at a position facing the photosensitive drums 11Y, 11M, 11C, and 11K so as to be in contact with the back surface of the transfer conveyance belt 8. 15M, 15C, and 15K are provided. 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 8, and a transfer electric field having a predetermined strength is generated between the transfer / conveyance belt 8 and the surface of the photosensitive drums 11Y, 11M, 11C, and 11K at each transfer position. Is formed. In addition, a backup roller 16 is provided in order to appropriately maintain the contact between the transfer paper 30 and the photosensitive drums 11Y, 11M, 11C, and 11K in the area where the transfer is performed and to obtain the best transfer nip.
The transfer bias applying members 15Y, 15M, and 15C and the backup roller 16 disposed in the vicinity thereof are integrally held by the swing bracket 23 so as to be rotatable, and can be rotated around a rotation shaft 24. This rotation is carried out clockwise as the cam 26 fixed to the cam shaft 27 rotates in the direction of the arrow.

The entrance roller 31 and the suction roller 18 are integrally supported by the entrance roller bracket 20 and can be rotated clockwise from the state of FIG. A hole 25 provided in the swing bracket 23 and a pin 22 fixed to the entrance roller bracket 20 are engaged with each other, so that they rotate in conjunction with the swing of the swing bracket 23.
By the clockwise rotation of the entrance roller bracket 20 and the swing bracket 23, the bias applying members 15Y, 15M, and 15C and the backup roller 16 disposed in the vicinity thereof are separated from the photosensitive drums 11Y, 11M, and 11C, and the entrance The roller 31 and the suction roller 18 also move downward. It is possible to avoid contact between the photoconductors 11Y, 11M, and 11C and the transfer conveyance belt 8 when forming a black-only image.
On the other hand, the transfer bias applying member 15K and the backup roller 16 adjacent to the transfer bias applying member 15K are rotatably supported by the outlet bracket 28, and are rotatable about a shaft 29 coaxial with the outlet roller 10 (FIG. 1).
When the transfer unit 6 is attached to or detached from the main body, the transfer unit 6 is rotated clockwise by operating a handle (not shown), and the transfer bias applying member 15K and the backup roller 16 adjacent thereto are transferred from the photosensitive drum 11K for black image formation. Are separated from each other.

A cleaning device 32 composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer / conveying belt 8 wound around the driving roller 12. The cleaning device 32 removes foreign matters such as toner adhering to the transfer / conveying belt 8.
A support roller 13 is provided downstream of the driving roller 12 in the traveling direction of the transfer conveying belt 8 in a direction to push the outer peripheral surface of the transfer conveying belt 8, and a winding angle around the driving roller 12 is secured. A tension roller 14 is provided in the loop of the transfer conveyance belt 8 further downstream than the support roller 13 to apply tension to the transfer conveyance belt with a pressing member (spring) 19.
The one-dot chain line in FIG. 1 shown above indicates the conveyance path of the transfer paper 30. The transfer paper 30 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 30 delivered at a predetermined timing by the registration roller pair 5 is carried on the transfer conveyance belt 8 and conveyed toward the toner image forming units 1Y, 1M, 1C, and 1K, and passes through the transfer nips. .
The toner images developed on the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming portions 1Y, 1M, 1C, and 1K are superimposed on the transfer paper 30 at the transfer nips, respectively. Transfered onto the transfer paper 30 under the action of pressure. A full-color toner image is formed on the transfer paper 30 by this superposition transfer.
The surfaces of the photoconductive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by the cleaning device 32, and are further discharged to prepare for the formation of the next electrostatic latent image.
After the full color toner image is fixed by the fixing unit 7, the transfer paper 30 on which the full color toner image is formed corresponds to the rotation position of the switching guide G, and the first discharge direction B or the second discharge direction. Head in paper 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.
When the paper is discharged in the second paper discharge direction C, it is conveyed to another post-processing device (such as a sorter or a binding device) (not shown) or registered again for double-sided printing via a switchback unit. It is conveyed to the roller pair 5.

Hereinafter, the bias condition applied to the electrostatic attraction roller provided in the laser printer according to this embodiment will be described. This is because the transfer paper that the applicant has sufficiently adsorbed to the belt is abnormal in the transfer nip portion. It was confirmed that problems such as discharge were caused, and the cause was found to be caused by imitating the distortion because the transfer paper was sufficiently attracted to the distortion accumulated on the belt. It is realized by this.
FIG. 3 is a characteristic diagram showing the operation of the suction bias controlled by the bias control means.
In the present embodiment, the suction bias applied to the electrostatic suction roller 18 by the bias control means 18b is set high at the front end of the transfer paper and low at the center.
As described above, in the present embodiment, the bias level of the electrostatic attraction roller s18 is set to be higher than the normal level at least once during the period in which the electrostatic attraction roller 18 is in contact with the transfer paper 30 by the bias control unit 18b. Control is performed so as to achieve a low distortion removal level. Thereby, it is possible to reduce the influence of the distortion of the transfer conveyance belt on the transfer paper, and it is possible to reduce the occurrence of abnormal images.
Note that the transfer paper leading edge position can be detected by synchronizing with the timing of a registration sensor (not shown), and the transfer paper length is mostly known in advance as the paper feed size. When the transfer paper length is indefinite, such as by manual feed, the device configuration that can detect the trailing edge of the transfer paper is common, so the timing required for this embodiment (the leading edge and the transfer paper length) It is also possible to know the leading edge and trailing edge).

FIG. 4 is a schematic diagram showing bias fluctuation when the bias between the normal level and the distortion removal level is continuously controlled.
The overall control is the same as described above, but since the bias is continuously changed, it is possible to prevent a sudden change in the transfer condition from appearing on the image.
The bias or current fluctuation between the normal level and the distortion removal level is continuously performed. Since the distortion of the transfer paper is not rapidly reduced, abnormal images such as color misregistration and transfer failure that may occur when the distortion is rapidly reduced can be prevented.
In the above example, the case of the transfer bias fixing control that is relatively easy to set has been described. However, in the bias fixing control in the electrophotographic transfer, particularly in the method of transferring directly to the transfer paper, it is not possible to correct the resistance fluctuation due to the difference in the type of the transfer paper, the resistance fluctuation due to the thickness, the environment, and the like.
FIG. 5 is a schematic diagram showing bias control based on current.
In consideration of the above, it is desirable that the reference of the bias applied to the electrostatic attraction roller 18 (FIG. 2) is performed by current rather than voltage. FIG. 5 shows that the feedback target for performing bias control for adsorption is current.
Regardless of the type of transfer paper or the environment, it achieves the effect of reducing distortion of the transfer paper.In other words, by using the current as a reference, the same amount of charge can be obtained even when the resistance value of the transfer paper is different. Can be given. As a result, a distortion reduction effect can be realized even for different transfer papers.

FIG. 6 is a schematic diagram showing the adsorption current control when the transfer sheets having different widths are continuously passed.
The above correction method is desirable for transfer paper of the same size, but the situation differs from the above case when the direction perpendicular to the transport direction, the so-called paper width, changes.
This is because even when the current is constant, if the area where the direct transfer conveyance belt is in contact with the photosensitive drum changes, the appropriate level of the adsorption current changes. In order to prevent such problems, it is possible to always realize stable suction by having a table that can switch the suction current according to the width of the transfer paper.
Accordingly, it is possible to correct a current change at an appropriate level due to a difference in the paper width of the transfer paper, and to correct a sneak current from the outside of the transfer paper, which is a problem with a small size. Therefore, it is possible to obtain an effect that it is possible to cope with a current change even for transfer papers of different sizes.
In the above embodiment, as shown in FIG. 1, the present invention is applied to a transfer unit 6 in a tandem printer in which a plurality of photosensitive drums 11Y, 11M, 11C, and 11K are arranged on a transfer conveyance belt 8. Applied. However, the printer and the belt driving device to which the present invention can be applied are not limited to this configuration.
In a printer having a belt driving device that rotationally drives an endless belt stretched around a plurality of rollers by at least one of the rollers, a roller for adsorbing the transfer paper to the transfer conveyance belt is configured. Any of them can be applied.

1 is a schematic configuration diagram illustrating an embodiment of a laser printer according to the present invention. FIG. 2 is an enlarged view showing a schematic configuration of a transfer unit in FIG. 1. It is a characteristic view which shows the operation | movement of the adsorption bias by the bias control means of this embodiment. It is the schematic which shows the fluctuation | variation of a bias in the case of controlling the bias of a normal level and a distortion removal level continuously. It is the schematic which shows the bias control on the basis of an electric current. It is the schematic which shows the adsorption current control when passing the transfer paper of a different width | variety continuously.

Explanation of symbols

  1Y toner image forming unit, 5 registration roller pair, 8 transfer conveyance belt, 11Y photosensitive drum, 18 electrostatic adsorption roller, 18a power supply, 30 transfer paper

Claims (5)

An endless transfer / conveying belt that is driven around and rotated by a plurality of rollers and carries the transferred transfer paper, and an outer peripheral surface of the transfer / conveying belt at a predetermined interval in the transfer paper conveying direction. A plurality of bias rollers to which a transfer bias is applied so as to be in contact with the back surface of the transfer conveyance belt, facing the plurality of image carriers in contact with each other, and the plurality of image carriers and the plurality of biases In the transfer device that superimposes and transfers the toner images on the plurality of image carriers onto the transfer paper on the transfer conveyance belt at each nip portion with a roller ,
One roller opposite to be arranged on the outer circumferential surface of the transfer conveyor belt the electric charges are provided to the transfer sheet on the transfer conveyor belt of the plurality of rollers at the transfer sheet conveyance direction upstream of the transfer conveyor belt An electrostatic adsorption roller for adhering the transfer paper to the transfer conveyance belt ;
Bias control means for controlling a bias level applied to the electrostatic attraction roller,
The bias control means sets a bias level of the electrostatic attraction roller when the electrostatic attraction roller contacts the transfer paper center during the period in which the electrostatic attraction roller is in contact with the transfer paper. A transfer apparatus, wherein the electroadhesion roller is controlled so as to be at a level lower than a normal level of the electrostatic attraction roller when the electroadhesion roller comes into contact with a front end portion and a rear end portion of the transfer paper.   The transfer apparatus according to claim 1, wherein the bias control unit continuously varies a bias level supplied to the electrostatic attraction roller.   The transfer device according to claim 1, wherein the bias controller is configured to apply a current to the bias applied to the electrostatic attraction roller.   The transfer apparatus according to claim 1, wherein the bias control unit includes a bias control table that changes the bias level in accordance with a width of the transfer sheet.   An image forming apparatus comprising the transfer device according to claim 1.

Images