Patent Application
20250085655
The present application claims priority from Japanese Application JP2023-148538, the content of which is hereby incorporated by reference into this application.
The present disclosure relates to an image forming apparatus.
Conventionally, it has been known that when an impact caused when a sheet enters a fixer is conveyed to the sheet and reaches a transferer, a toner image being transferred is disturbed, and image quality is deteriorated. In addition, as is conventionally known, it is possible to suppress propagation of the impact which may cause deterioration in image quality as described above by bending the sheet between the transferer and the fixer.
However, in a case where an image is printed on thick paper, there is a case that propagation of the impact cannot be suppressed, even when the thick paper is bent because the thick paper is hard. Further, the impact caused when the thick paper enters the fixer is large, as compared with plain paper.
The present disclosure has been made in view of the above circumstances, and provides an image forming apparatus capable of suppressing deterioration in image quality caused when a leading end of a sheet passes through a fixing nip.
An image forming apparatus according to an aspect of the present disclosure includes: a transferer provided to transfer a toner image on an image carrier onto a sheet, and facing the image carrier; a fixer provided to fix the toner image on the sheet; and a controller provided to apply transfer voltage for transferring the toner image onto the sheet. The transferer is provided to define a transfer nip for passing the sheet between the image carrier and the transferer. The fixer includes a heating portion and a pressing portion, and is provided to pass the sheet that has passed through the transfer nip through a fixing nip between the heating portion and the pressing portion. The controller is provided to control the transfer voltage in such a way that transfer current flowing through the transfer nip is made constant at a setting value, and is provided to increase the setting value of transfer current after a leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip.
According to the present disclosure, it is possible to suppress deterioration in image quality caused when a leading end of a sheet passes through a fixing nip.
An image forming apparatus according to the present disclosure includes: a transferer that transfers a toner image on an image carrier onto a sheet, and facing the image carrier; a fixer that fixes the toner image on the sheet; and a controller that applies transfer voltage for transferring the toner image onto the sheet. The transferer defines a transfer nip for passing the sheet between the image carrier and the transferer. The fixer includes a rotatable heating portion and a rotatable pressing portion, and passes the sheet that has passed through the transfer nip through a fixing nip between the heating portion and the pressing portion. The controller controls the transfer voltage in such a way that transfer current flowing through the transfer nip is made constant at a setting value, and increases the setting value of transfer current after a leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip.
Preferably, the controller may increase the setting value of transfer current after the leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip, and decrease the setting value of transfer current after the leading end of the sheet that has passes through the transfer nip passes through the fixing nip. Preferably, a transport distance of the sheet from an increase in the setting value of transfer current to a decrease in the setting value of transfer current may be 13 mm or more and 30 mm or less.
Preferably, the controller may determine whether to increase the setting value of transfer current after the leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip, based on a type of the sheet passing through the transfer nip. Preferably, in a case where the sheet is plain paper, the controller may make the setting value of transfer current constant while the sheet passes through the transfer nip, and in a case where the sheet is thick paper, the controller may increase the setting value of transfer current after the leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip.
Preferably, the controller may determine whether to increase the setting value of transfer current after the leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip, based on an electrical resistance value between a front surface and a back surface of the sheet. Preferably, the image forming apparatus may further include a sensor section that measures an electrical resistance value between a front surface and a back surface of the sheet, and the controller may determine whether to increase the setting value of transfer current after the leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip, based on an electrical resistance value measured by the sensor section. Preferably, the controller may make the setting value of transfer current constant while the sheet passes through the transfer nip, in a case where a toner image being a text is transferred onto the sheet in the transfer nip at timing when the leading end of the sheet passes through the fixing nip, and the controller may increase the setting value of transfer current after the leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip, in a case where a toner image being an image is transferred onto the sheet in the transfer nip at timing when the leading end of the sheet passes through the fixing nip.
Preferably, the controller may increase the setting value of transfer current after the leading end of the sheet passes through the transfer nip and before the leading end of the sheet passes through the fixing nip, in a case where an amount of cyan toner or yellow toner contained in a toner image to be transferred onto the sheet in the transfer nip is larger than a predetermined value at timing when the leading end of the sheet passes through the fixing nip. Preferably, the controller may adjust an amount of increase in the setting value of transfer current, based on a type of the sheet passing through the transfer nip, an electrical resistance value between a front surface and a back surface of the sheet, or an amount of cyan toner or yellow toner contained in a toner image to be transferred onto the sheet in the transfer nip at timing when the leading end of the sheet passes through the fixing nip.
Hereinafter, an embodiment of the present disclosure is described by using the drawings. Drawings and configurations described in the following description are an example, and the scope of the present disclosure is not limited to the drawings and configurations described in the following description.
An image forming apparatus 50 according to the present embodiment includes: a transferer 8 provided in such a way as to transfer a toner image on an image carrier 20 onto a sheet 3, and facing the image carrier 20; a fixer 28 provided in such a way as to fix the toner image on the sheet 3; and a controller 7 provided in such a way as to apply transfer voltage for transferring the toner image onto the sheet 3. The transferer 8 is provided in such a way as to define a transfer nip 24 for passing the sheet 3 between the image carrier 20 and the transferer 8. The fixer 28 includes a rotatable heating portion 25 and a rotatable pressing portion 26, and is provided in such a way as to pass the sheet 3 that has passed through the transfer nip 24 through a fixing nip 27 between the heating portion 25 and the pressing portion 26. The controller 7 is provided in such a way as to control the transfer voltage in such a way that transfer current flowing through the transfer nip 24 is made constant at a setting value, and is provided in such a way as to increase the setting value of transfer current after a leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27.
The image forming apparatus 50 is an image forming apparatus of an electrophotographic method that forms an image by using an electrophotographic technique. The image forming apparatus 50 may be a monochromatic image forming apparatus capable of forming a monochromatic image, or may be a color image forming apparatus of an intermediate transfer method capable of forming a color image as illustrated in
The controller 7 is a portion that controls the image forming apparatus 50. The controller 7 may include, for example, an arithmetic processing device (e.g., a CPU), a RAM, a storage device (e.g., an HDD), a network controller, a video controller, a power supply portion, and the like. Further, the controller 7 is provided in such a way as to apply transfer voltage between an intermediate transfer belt roller 13a and the transferer 8. By applying the transfer voltage, transfer current is allowed to flow through the transfer nip 24, and a toner image on the intermediate transfer belt 20 (image carrier) can be transferred onto the sheet 3. Further, the controller 7 is provided in such a way as to control transfer voltage in such a way that transfer current flowing through the transfer nip 24 (the direction in which current flows is constant) is made constant at a setting value (constant current control). Further, the controller 7 is provided in such a way that the setting value of transfer current can be changed while the sheet 3 passes through the transfer nip 24. Further, the controller 7 can control transport, transfer timing, and the like of the sheet 3 on a sheet transport path 2 by controlling rotation of transport rollers 4a to 4k, registration rollers 5, the pressing portion 26, intermediate transfer belt rollers 13a to 13h, transferer rollers 12a to 12f, and the like.
The toner image formers 18a to 18d include photoconductors 19a to 19d, chargers, an exposure unit 33, developing units, transfer means, and cleaning units. The photoconductors 19a to 19d are members having a surface on which a latent image and a toner image are formed. By rotating the photoconductors 19a to 19d, a toner image of black toner, a toner image of cyan toner, a toner image of magenta toner, or a toner image of yellow toner is successively formed based on image data. The photoconductors 19a to 19d are, for example, a photosensitive drum. The charger, the exposure unit 33, the developing unit, the transfer means, and the cleaning unit are provided in this order from upstream toward downstream in the rotating direction of the photoconductors 19a to 19d along an outer peripheral surface of the photoconductors 19a to 19d. Toner may be negatively charged, or may be positively charged.
A toner image of black toner, a toner image of cyan toner, a toner image of magenta toner, and a toner image of yellow toner formed on the photoconductors 19a to 19d are transferred to the intermediate transfer belt 20 by Coulomb force or the like due to a primary transfer electric field (primary transfer), and are superimposed one over another. Thus, a color toner image is formed on the intermediate transfer belt 20. The color toner image on the intermediate transfer belt 20 being driven by the intermediate transfer belt rollers 13a to 13h is transferred onto the sheet 3 being transported on the sheet transport path 2 by Coulomb force or the like due to a secondary transfer electric field generated by transfer voltage in the transferer 8 (secondary transfer).
The transferer 8 is a portion provided in such a way as to transfer a toner image on the intermediate transfer belt 20 (image carrier) onto the sheet 3. The transferer 8 may be a transfer roller, or as illustrated in
A sheet transport device is a device that transports a sheet along the sheet transport path 2. The sheet transport device can include the sheet transport path 2, the transport rollers 4a to 4k, the registration rollers 5, the transferer 8, the fixer 28, a sheet feeding tray 21, a manual feed tray 22, a sheet discharge tray 23, and the like. Further, the sheet transport device can include a plurality of sheet sensors. Sheet transport by the sheet transport device is controlled by a control signal to be transmitted from the controller 7 to a motor that rotates each roller. Further, the sheet transport device can include a sensor section provided in such a way as to measure an electrical resistance value (penetrating electrical resistance value) between a front surface and a back surface of the sheet 3.
The sheet transport device is provided in such a way as to pick up the sheet 3 from the sheet feeding tray 21 or the manual feed tray 22, a color toner image on the intermediate transfer belt 20 is transferred onto the sheet 3 in the transferer 8, the color toner image is fixed on the sheet 3 in the fixer 28, and the sheet 3 having the color toner image is discharged to the sheet discharge tray.
The fixer 28 includes the rotatable heating portion 25, the rotatable pressing portion 26, and a fixer motor 29 provided in such a way as to rotate the heating portion 25 and the pressing portion 26, and is provided in such a way that the sheet 3 that has passed through the transfer nip 24 passes through the fixing nip 27 between the heating portion 25 and the pressing portion 26.
The fixer motor 29 is a motor provided in such a way as to drive one of the heating portion 25 and the pressing portion 26. In
The heating portion 25 is a portion for heating a toner image on the sheet 3 passing through the fixing nip 27, and the pressing portion 26 is a portion for applying pressure to the sheet 3 passing through the fixing nip 27. Allowing the fixer 28 to include the heating portion 25 and the pressing portion 26 enables to fix a toner image on the sheet 3 by fusing and pressing the toner image. The heating portion 25 may be a heating roller or may be a heating belt, or may include a configuration in which a roller and a belt are combined. The pressing portion 26 may be a pressing roller, or may be a pressing belt.
The controller 7 is provided in such a way as to make a setting value of transfer current larger than a normal value after a leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27. Further, the controller 7 can make a setting value of transfer current constant after making the setting value of transfer current larger than the normal value and while the leading end of the sheet 3 passes through the fixing nip 27. This enables to suppress deterioration in image quality caused when the leading end of the sheet 3 passes through the fixing nip 27. A reason for this is not clear, but it is conceived that electric field strength of a secondary transfer electric field increases by increasing transfer current, and even when an impact caused when the leading end of the sheet 3 enters the fixing nip 27 is conveyed to the sheet 3 and reaches the transfer nip 24, generation of disturbance in transfer of a toner image onto the sheet 3 is suppressed. The normal value of the setting value of transfer current is, for example, 50 μA or more and 120 μA or less. The normal value is a setting value of transfer current to be set when transfer of a toner image onto the sheet 3 is started. The normal value of the setting value of transfer current can be changed depending on a type o the sheet 3 passing through the transfer nip 24. An amount of increase in the setting value of transfer current is, for example, 20 μA or more and 120 μA or less.
The controller 7 may be provided in such a way as to increase the setting value of transfer current after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27, and to decrease the setting value of transfer current after the leading end of the sheet 3 passing through the transfer nip 24 passes through the fixing nip 27. This enables to suppress occurrence of voids, white spots, and the like in a printed image.
Herein, control of transfer current by the controller 7 at the time of printing on thick paper (sheet 3) is described by using
Timing when the controller 7 returns the setting value of transfer current to the normal value after the leading end of the sheet 3 exits the fixing nip 27 is not particularly limited, as long as the timing is after the leading end of the sheet 3 exits the fixing nip 27. For example, in the graphs illustrated in
The controller 7 may be provided in such a way as to determine whether to increase the setting value of transfer current after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27, based on a type of the sheet 3 passing through the transfer nip 24. The controller 7 can determine the type of the sheet 3, based on, for example, print settings to be set by a user, or a sheet feeding tray to be used. In a case where the controller 7 determines that the sheet 3 is plain paper, the controller 7 can make the setting value of transfer current constant at the normal value, while the sheet 3 passes through the transfer nip 24. In a case where the controller 7 determines that the sheet 3 is thick paper, the controller 7 can increase the setting value of transfer current from the normal value after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27.
The controller 7 may be provided in such a way as to determine whether to increase the setting value of transfer current from the normal value after the leading end the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27, based on an electrical resistance value (penetrating electrical resistance value) between a front surface and a back surface of the sheet 3. The controller 7 can determine the penetrating electric resistance value of the sheet 3, based on, for example, print settings to be set by a user, or a sheet feeding tray to be used. In this case, the controller 7 may store a penetrating electric resistance value of the sheet 3 that is measured in advance. For example, in a case where the penetrating electric resistance value of the sheet is smaller than a predetermined threshold value, the controller 7 can make the setting value of transfer current constant at a normal value, while the sheet 3 passes through the transfer nip 24. Further, when the penetrating electric resistance value of the sheet is larger than the predetermined threshold value, the controller 7 can increase the setting value of transfer current from the normal value after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27.
In a case where the penetrating electrical resistance value of the sheet 3 is large, since electric field strength of a secondary transfer electric field to be formed in the transfer nip 24 during passing of the sheet may decrease, it is possible to suppress deterioration in image quality by increasing the setting value of transfer current while the leading end of the sheet 3 passes through the fixing nip 27.
The image forming apparatus 50 may include a sensor section provided in such a way as to measure an electrical resistance value between a front surface and a back surface of the sheet 3. The sensor section can include, for example, two conductive rollers provided in such a way as to sandwich the sheet transport path 2, and a measurement portion provided in such a way as to measure an electrical resistance value of the sheet 3 passing between the two conductive rollers. The controller 7 may be provided in such a way as to determine whether to increase the setting value of transfer current from the normal value after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27, based on the electrical resistance value measured by the sensor section. For example, in a case where an electrical resistance value measured by the sensor section is smaller than a predetermined threshold value, the controller 7 can make the setting value of transfer current constant at a normal value, while the sheet 3 passes through the transfer nip 24. Further, in a case where an electric resistance value is larger than the predetermined threshold value measured by the sensor, the controller 7 can increase the setting value of transfer current from the normal value after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27.
The controller 7 may be provided in such a way as to make the setting value of transfer current constant at a normal value, while the sheet 3 passes through the transfer nip 24, when a toner image being a text is transferred onto the sheet 3 in the transfer nip 24 at timing when the leading end of the sheet 3 passes through the fixing nip 27. Further, the controller 7 may be provided in such a way as to increase the setting value of transfer current from the normal value after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27, when a toner image being an image (e.g., a solid image) is transferred onto the sheet 3 in the transfer nip 24 at timing when the leading end of the sheet 3 passes through the fixing nip 27. Since image quality is likely to be deteriorated in an image, as compared with a text due to an impact caused when the leading end of the sheet 3 enters the fixing nip 27, it is possible to suppress deterioration in image quality by increasing the setting value of transfer current from the normal value when the image is printed.
The controller 7 may be provided to increase the setting value of transfer current from a normal value after the leading end of the sheet 3 passes through the transfer nip 24 and before the leading end of the sheet 3 passes through the fixing nip 27, when an amount of cyan toner or yellow toner contained in a toner image to be transferred onto the sheet 3 is larger than a predetermined value in the transfer nip 24 at timing when the leading end of the sheet 3 passes through the fixing nip 27; and make the setting value of transfer current constant at the normal value, while the sheet 3 passes through the transfer nip 24, when the amount of cyan toner or yellow toner is smaller than the predetermined value. Since image quality is likely to be deteriorated in an image in which an amount of cyan toner or yellow toner is large due to an impact caused when the leading end of the sheet 3 enters the fixing nip 27, it is possible to suppress deterioration in image quality by increasing the setting value of transfer current from the normal value, when the image in which the amount of cyan toner or yellow toner is large is printed.
The controller 7 may be provided in such a way as to adjust an amount of increase in the setting value of transfer current from the normal value, based on a type of the sheet 3 passing through the transfer nip 24, an electrical resistance value (penetrating electrical resistance value) between a front surface and a back surface of the sheet 3, or an amount of cyan toner or yellow toner contained in a toner image to be transferred onto the sheet 3 in the transfer nip 24 at timing when the leading end of the sheet 3 passes through the fixing nip 27. For example, when printing is performed on the sheet 3 which is likely to cause deterioration in image quality, when printing is performed on the sheet 3 having a particularly large penetrating electrical resistance value, when an image having a large amount of cyan toner is printed, or the like, as illustrated in the graph in
A blue image was printed on an A4 size sheet having a basis weight of 360 g/m2 by using a digital full color multifunction peripheral manufactured by Sharp Corporation. In the printing as an example, as illustrated in the graph in
In the printed image of the comparative example, a light and shade stripe (banding) of toner appeared in a portion where transfer was performed in the transfer nip at timing when the leading end of the sheet passed through the fixer. In the printed image of the example, a light and shade stripe (banding) of toner which appeared in the comparative example did not appear. Therefore, it has been found that deterioration in image quality can be suppressed by increasing the setting value of transfer current when the leading end of the sheet passes through the fixer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-148538 | Sep 2023 | JP | national |
