This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No 2021-028360 filed on Feb. 25, 2021, the entire contents of which are hereby incorporated by reference.
The present disclosure relates to a transfer unit for transferring to a recording medium a toner image formed on an image carrying member such as a photosensitive drum or an intermediate transfer belt, and to an image forming apparatus provided with such a transfer unit. More particularly, the present disclosure relates to a mechanism for switching the arrangement of a plurality of transfer members.
Conventionally, there is a known intermediate transfer-type image forming apparatus including an endless intermediate transfer belt that rotates in a prescribed direction and a plurality of image forming portions provided along the intermediate transfer belt. In the image forming apparatus, by the image forming portions, toner images of respective colors are primarily transferred to the intermediate transfer belt by being sequentially superimposed on each other, after which the toner images are secondarily transferred by a secondary transfer roller to a recording medium such as paper.
In such intermediate transfer-type image forming apparatuses, adhesion of toner to the surface of the secondary transfer roller accumulates due to durable printing. In particular, to improve color development and color reproducibility, it is necessary to execute calibration for correcting image density and color displacement with predetermined timing, and a patch image formed on the intermediate transfer belt during execution of calibration is, instead of being transferred to the recording medium, removed by a belt cleaning device. This causes, as the patch image passes through the secondary transfer roller, part of the toner transferred to the intermediate transfer belt to adhere to the secondary transfer roller.
Conventionally, the secondary transfer roller is cleaned by applying a reverse transfer voltage (a voltage with the same polarity as the toner) to the secondary transfer roller during a non-image forming period to move the toner deposited on the secondary transfer roller back to the intermediate transfer belt. However, this method is disadvantageous in that cleaning of the secondary transfer roller takes time, resulting in longer printing wait time.
To cope with that, there have been proposed methods for improving productivity by permitting switching of the secondary transfer roller to the one of the size appropriate to the recording medium, and, for example, there is a known image forming apparatus that includes a plurality of secondary transfer rollers having different lengths in the axial direction, a rotary member having a supporting portion that rotatably supports the plurality of secondary transfer rollers and that is pivotable about an axis parallel to the axial direction, and a control portion that selects one roller out of the plurality of secondary transfer rollers in accordance with the width of the recording medium and rotates the supporting portion to arrange the roller opposite the intermediate transfer belt.
According to one aspect of the present disclosure, a transfer unit includes a transfer roller having a metal shaft and an elastic layer laid around a circumferential face of the metal shaft to form a transfer nip by keeping the elastic layer in pressed contact with an image carrying member, and transfers a toner image formed on the image carrying member to a recording medium as it passes through the transfer nip. The transfer unit includes, as transfer rollers, a first roller and a second roller, a first bearing member, a second bearing member, a roller holder, a first urging member, a second urging member, a first switching cam, a second switching cam, and a driving mechanism. The second roller has an elastic layer longer in an axial direction than that of the first roller. The first bearing member rotatably supports the first roller. The second bearing member rotatably supports the second roller. The roller holder has a first bearing holding portion and a second bearing holding portion that respectively hold the first and second bearing members slidably in directions toward and away from the image carrying member. The first urging member is arranged between the first bearing holding portion and the first bearing member and urges the first bearing member in the direction toward the image carrying member. The second urging member is arranged between the second bearing holding portion and the second bearing member and urges the second bearing member in the direction toward the image carrying member. The first switching cam has a first guide hole with which a first engaging portion formed on the first bearing member engage. The second switching cam has a second guide hole with which a second engaging portion formed on the second bearing member engage. The driving mechanism drives the roller holder and the first and second switching cams to rotate. By rotating the roller holder, one of the first and second rollers is arranged opposite the image carrying member, and, by rotating the first and second switching cams to change positions at which the first and second engaging portions engage with the first and second guide holes respectively, the first or second roller that is arranged opposite the image carrying member is arranged selectively either at a reference position at which the first or second roller is kept in pressed contact with the image carrying member to form the transfer nip or at a released position at which the first or second roller lies away from the image carrying member.
Hereinafter, with reference to the accompanying drawings, embodiments of the present disclosure will be described.
The image forming apparatus 100 shown in
In these image forming portions Pa to Pd, photosensitive drums 1a, 1b, 1c, and 1d are respectively arranged which carry visible images (toner images) of the different colors. Furthermore, an intermediate transfer belt 8 which rotates counter-clockwise in
The sheet S to which the toner images are transferred is stored in a sheet cassette 16 arranged in a lower part of the main body of the image forming apparatus 100, and is conveyed via a sheet feeding roller 12a and a pair of registration rollers 12b to the secondary transfer unit 9. Used typically as the intermediate transfer belt 8 is a belt without seams (seamless belt).
Next, a description will be given of the image forming portions Pa to Pd. The image forming portion Pa will be described in detail below. Since the image forming portions Pb to Pd have basically similar structures, no overlapping description will be repeated. As shown in
Next, a description will be given of an image forming procedure on the image forming apparatus 100. When a user enters an instruction to start image formation, first, a main motor 60 (see
The developing devices 3a to 3d are loaded with predetermined amounts of toner of magenta, cyan, yellow, and black respectively. When, through formation of toner images, which will be described later, the proportion of toner in a two-component developer stored in the developing devices 3a to 3d falls below a determined value, toner is supplied from toner containers 4a to 4d to the developing devices 3a to 3d respectively. The toner in the developer is fed from developing rollers 21 in the developing devices 3a to 3d to the photosensitive drums 1a to 1d respectively, and electrostatically attaches to them. In this way, toner images corresponding to the electrostatic latent images formed through exposure to light from the exposure device 5 are formed.
Then, the primary transfer rollers 6a to 6d apply electric fields of a prescribed transfer voltage between themselves and the photosensitive drums 1a to 1d, and thus the toner images of magenta, cyan, yellow, and black respectively on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These images of four colors are formed in a predetermined positional relationship with each other that is prescribed for formation of a predetermined full-color image. After that, in preparation for the subsequent formation of new electrostatic latent images, the residual toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by cleaning blades 22 and rubbing rollers 23 in the cleaning devices 7a to 7d.
As a driving roller 10 is driven to rotate by a belt drive motor 61 (see
The sheet S conveyed to the fixing portion 13 is heated and pressed by a pair of fixing rollers 13a so that the toner images are fixed on the surface of the sheet S, and thus the prescribed full-color image is formed on it. The conveyance direction of the sheet S on which the full-color image has been formed is switched by a branch portion 14 branching into a plurality of directions, and thus the sheet S is directly (or after being conveyed to a double-sided conveyance path 18 and thus being subjected to double-sided printing) discharged onto a discharge tray 17 by a pair of discharge rollers 15.
An image density sensor 25 is arranged at a position opposite the driving roller 10 via the intermediate transfer belt 8. As the image density sensor 25, an optical sensor is typically used that includes a light-emitting element formed of an LED or the like and a light-receiving element formed of a photodiode or the like. To measure the amount of toner attached to the intermediate transfer belt 8, patch images (reference images) formed on the intermediate transfer belt 8 are irradiated with measurement light from the light-emitting element, so that the measurement light strikes the light-receiving element as light reflected by the toner and light reflected by the belt surface.
The light reflected from the toner and the belt surface includes a regularly reflected light component and an irregularly reflected light component. The regularly and irregularly reflected light are separated with a polarization splitting prism and strike separate light-receiving elements respectively. Each of the light-receiving elements performs photoelectric conversion on the received regularly or irregularly reflected light and outputs an output signal to a control portion 90 (see
Then, from the change in the characteristics of the output signals with respect to the regularly and irregularly reflected light, the image density (toner amount) and the image position in the patch images are determined and compared with a predetermined reference density and a predetermined reference position to adjust the characteristic value of the developing voltage, the start position and the start timing of exposure by the exposure device 5, and so on. In this way, for each of the different colors, density correction and color displacement correction (calibration) are performed.
The belt cleaning unit 19 for removing the residual toner remaining on the surface of the intermediate transfer belt 8 is arranged at a position opposite the tension roller 11. With the driving roller 10, the secondary transfer unit 9 is kept in pressed contact via the intermediate transfer belt 8, forming a secondary transfer nip N. The detailed configuration of the secondary transfer unit 9 will be described later.
The intermediate transfer unit 30 includes a roller contact/release mechanism 35 including a pair of support members (not shown) that supports the opposite ends of a rotary shaft of each of the primary transfer rollers 6a to 6d and the pressing state switching roller 34 so that they are rotatable and movable perpendicularly (in the up-down direction in
As shown in
The first and second rollers 40 and 41 are elastic rollers respectively having electrically conductive elastic layers 40b and 41b laid around outer circumferential faces of metal shafts 40a and 41a respectively. Used as the material for the elastic layers 40b and 41b is, for example, ion conductive rubber such as ECO (epichlorohydrin rubber).
The elastic layer 40b of the first roller 40 is 311 millimeters long in the axial direction and is compatible with the A3-size sheet. The elastic layer 41b of the second roller 41 is longer than the elastic layer 40b of the first roller 40 in the axial direction. More specifically, the elastic layer 41b is 325 millimeters long in the axial direction and is compatible with a 13 inch-size sheet.
A pair of first bearing members 43 are arranged in opposite end parts of the first roller 40 in the axial direction so as to rotatably support the metal shaft 40a. A pair of second bearing members 45 are arranged in opposite end parts of the second roller 41 in the axial direction so as to rotatably support the metal shaft 41a.
A pair of roller holders 47 are arranged in opposite end parts of the first and second rollers 40 and 41 in the axial direction. The roller holder 47 is in a V-shape as seen in a side view and has a first bearing holding portion 47a, a second bearing holding portion 47b, and an insertion hole 47c. The first and second bearing holding portions 47a and 47b slidably support the first and second bearing members 43 and 45 respectively. The insertion hole 47c is formed near the vertex of the V-shape, and is rotatably penetrated by a shaft 52. The roller holder 47 is formed of an electrically insulating material such as synthetic resin.
As shown in
As shown in
The first light-shielding plate 52a and the second light-shielding plate 47d turn on and off the first and second position sensors S1 and S2 respectively in accordance with the rotating angle of the roller holder 47 (shaft 52), and this makes it possible to sense the position of the first and second rollers 40 and 41 supported on the roller holder 47. The control for sensing the position of the first and second rollers 40 and 41 will be described later.
A pair of first switching cams 50 are arranged in opposite end parts of the first and second rollers 40 and 41 in the axial direction, inward of the roller holders 47. A pair of second switching cams 51 are arranged in opposite end parts of the first and second rollers 40 and 41 in the axial direction, outward of the roller holders 47. The first and second switching cams 50 and 51 are in a partly cut-off fan shape as seen in a side view, with the hinge portion of the fan shape (near the vertex at which two radial lines intersect) fastened to the shaft 52.
As shown in
The control portion 90 includes at least a CPU (central processing unit) 91 as a central arithmetic processor, a ROM (read-only memory) 92 as a read-only storage portion, a RAM (random-access memory) 93 as a readable/writable storage portion, a temporary storage portion 94 that temporarily stores image data or the like, a counter 95, and a plurality of (here, two) I/Fs (interfaces) 96 that transmit control signals to different devices in the image forming apparatus 100 and receive input signals from an operation section 80. Furthermore, the control portion 90 can be arranged at any location inside the main body of the image forming apparatus 100.
The ROM 92 stores data and the like that are not changed during use of the image forming apparatus 100, such as control programs for the image forming apparatus 100 and numerical values required for control. The RAM 93 stores necessary data generated in the course of controlling the image forming apparatus 100, data temporarily required for control of the image forming apparatus 100, and the like. Furthermore, the RAM 93 (or the ROM 92) also stores a density correction table used in calibration, and the like. The counter 95 counts the number of sheets printed in a cumulative manner.
The control portion 90 transmits control signals to different parts and devices in the image forming apparatus 100 from the CPU 91 through the I/F 96. From the different parts and devices, signals that indicate their statuses and input signals are transmitted through the I/F 96 to the CPU 91. Examples of the various portions and devices controlled by the control portion 90 include the image forming portions Pa to Pd, the exposure device 5, the primary transfer rollers 6a to 6d, the secondary transfer unit 9, the roller contact/release mechanism 35, the main motor 60, the belt drive motor 61, an image input portion 70, a voltage control circuit 71, and the operation section 80.
The image input portion 70 is a receiving portion that receives image data transmitted from a host apparatus such as a personal computer to the image forming apparatus 100. An image signal inputted from the image input portion 70 is converted into a digital signal, which then is fed out to the temporary storage portion 94.
The voltage control circuit 71 is connected to a charging voltage power supply 72, a developing voltage power supply 73, and a transfer voltage power supply 74, and makes those power supplies operate according to output signals from the control portion 90. In response to control signals from the voltage control circuit 71, the charging voltage power supply 72, the developing voltage power supply 73, and the transfer voltage power supply 74 apply predetermined voltages to the charging roller 20 in the charging devices 2a to 2d, to the developing roller 21 in the developing devices 3a to 3d, to the primary transfer rollers 6a to 6d and the first and second rollers 40 and 41 in the secondary transfer unit 9 respectively.
The operation section 80 includes a liquid crystal display portion 81 and LEDs 82 that indicate various statuses. A user operates a stop/clear button on the operation section 80 to stop image formation and operates a reset button on it to bring various settings for the image forming apparatus 100 to default ones. The liquid crystal display portion 81 indicates the status of the image forming apparatus 100 and displays the progress of image formation and the number of copies printed. Various settings for the image forming apparatus 100 are made via a printer driver on a personal computer.
Next, a description will be given of switching control and position sensing control for the first and second rollers 40 and 41 in the secondary transfer unit 9 according to the embodiment.
As shown in
As shown in
In the state in
The first light-shielding plate 52a (see
When the first roller 40 is kept in pressed contact with the driving roller 10 for a long time, the first roller 40 may yield and deform in the axial direction. To avoid that, after a job, the first roller 40 needs to be kept away from the intermediate transfer belt 8 (driving roller 10). This is achieved in the first released state shown in
The first light-shielding plate 52a on the shaft 52 is retracted from the sensing portion of the first position sensor S1 (off), and the second light-shielding plate 47d on the roller holder 47 keeps shielding light from the sensing portion of the second position sensor S2 (on). That is, when the sensing state changes from the one in
The sensing state of the first and second position sensors S1 and S2 in
To shift the first roller 40 in the second released state back to the reference position, it is necessary to rotate the roller holder 47 and the first and second switching cams 50 and 51 counter-clockwise first to switch to the reference position of the second roller 41 (see
Next, a description will be given of a procedure for switching the roller that forms the secondary transfer nip N from the first roller 40 to the second roller 41. When the shaft 52 is rotated counter-clockwise from the second released state shown in
When the roller holder 47 rotates until it makes contact with a restriction rib 9c (see
As a result, the second roller 41 is kept in pressed contact with the driving roller 10 via the intermediate transfer belt 8 to form the secondary transfer nip N and rotates by following the driving roller 10. To the second roller 41, a transfer voltage of the polarity (here, negative) opposite to that of toner is applied by the transfer voltage power supply 74 (see
The first light-shielding plate 52a on the shaft 52 shields light from the sensing portion of the first position sensor S1 (on), and the second light-shielding plate 47d on the roller holder 47 is retracted from the sensing portion of the second position sensor S2 (off). This state (S1 on/S2 off) is taken as the reference position (home position) of the second roller 41. That is, when the sensed state changes from the one in
When the second roller 41 is kept in pressed contact with the driving roller 10 for a long time, the second roller 41 may yield and deform in the axial direction. To avoid that, after a job, the second roller 41 needs to be kept away from the intermediate transfer belt 8 (driving roller 10). This is achieved in the first released state shown in
The first light-shielding plate 52a on the shaft 52 is retracted from the sensing portion of the first position sensor S1 (off), and the second light-shielding plate 47d on the roller holder 47 is kept retracted from the sensing portion of the second position sensor S2 (off). That is, when the sensing state changes from the one in
The sensing state of the first and second position sensors S1 and S2 in
To shift the second roller 41 in the second released state back to the reference position, it is necessary to rotate the roller holder 47 and the second switching cam 51 clockwise first to switch to the reference position of the first roller 40 (see
When the roller that forms the secondary transfer nip N is switched from the second roller 41 to the first roller 40, the shaft 52 is rotated from the second released state shown in
With a structure according to the embodiment, with a simple configuration using the roller holder 47 and the first and second switching cams 50 and 51, it is possible to arrange one of the first and second rollers 40 and 41 opposite the driving roller 10 and to selectively arrange the first or second roller 40 or 41 arranged opposite the driving roller 10 either at the reference position at which it forms the secondary transfer nip N or at the released position at which it lies away from the intermediate transfer belt 8.
For example, if the sheet S is equal to or smaller than a predetermined size (here, A3 size), the first roller 40 with the smaller elastic layer 40b in the axial direction is arranged at the reference position. Then, when calibration is performed during image formation in which the reference image is formed on the intermediate transfer belt 8 outside the image area in the width direction (outside the first roller 40 in the axial direction), the reference image formed on the intermediate transfer belt 8 does not make contact with the first roller 40. Thus, calibration can be performed during image formation, and this helps improve image quality without a drop in image processing efficiency (productivity).
It is also possible to effectively suppress staining on the rear surface of the sheet S due to toner adhering to the first roller 40. Furthermore, it is not necessary to perform cleaning operation to move the toner deposited on the first roller 40 back to the intermediate transfer belt 8, and this helps reduce printing wait time.
By contrast, if the sheet S is larger than the predetermined size (here, 13 inch size), the second roller 41 with the elastic layer 41b larger in the axial direction is arranged at the reference position. Then, it is possible to ensure that the toner image is secondarily transferred to the opposite edge parts of the large-size sheet S in the width direction.
Switching the arrangement of the first and second rollers 40 and 41 using the first and second switching cams 50 and 51 respectively, compared to switching the arrangement of the first and second rollers 40 and 41 using a single switching cam, helps reduce the rotating angle of the switching cam (to ½). Thus, there is no need to secure a large space to allow the rotation of the first and second switching cams 50 and 51, and this helps reduce the size of the secondary transfer unit 9.
In this embodiment, it is possible to switch the released position of the first and second rollers 40 and 41 between the first released state with a smaller distance from the intermediate transfer belt 8 and the second released state with a larger distance from it. Thus, when, after a job, the first and second rollers 40 and 41 are laid away from the driving roller 10 to prevent their deformation, if calibration is executed during use of the second roller 41, laying the first and second rollers 40 and 41 in the first released state helps reduce the time until they are arranged at the reference position at which they form the secondary transfer nip N. Thus, it is possible to minimize a drop in image processing efficiency (productivity) due to the movement of the first and second rollers 40 and 41.
Furthermore, in this embodiment, it is possible to drive the roller holder 47 and the first and second switching cams 50 and 51 with the single roller switching motor 55. Thus, compared to a configuration where the roller holder 47 and the first and second switching cams 50 and 51 are driven with separate motors, the driving mechanism and the driving control can be simplified, and this helps reduce the cost and the size of the image forming apparatus 100.
The embodiment described above is in no way meant to limit the present disclosure, which thus allows for many modifications and variations within the spirit of the present disclosure. For example, the shapes and the dimensions of the first roller 40, the second roller 41, the roller holder 47, the first and the second switching cams 50 and 51 that constitute the secondary transfer unit 9 are merely examples and can be freely modified without spoiling the effect of the present disclosure.
In the embodiment described above, the first and second position sensors S1 and S2 are used to restrict the rotating angle of the first and second switching cams 50 and 51 and to sense the arrangement and the released state of the first and second rollers 40 and 41; instead, for example, as shown in
Although the above embodiment deals with, as an example, an intermediate transfer-type image forming apparatus 100 provided with the secondary transfer unit 9 by which the toner image that has been primarily transferred to the intermediate transfer belt 8 is secondarily transferred to the sheet S, what is disclosed herein is applicable similarly to transfer units mounted on a direct transfer-type image forming apparatus in which a toner image formed on the photosensitive drum is directly transferred to the sheet.
The present disclosure is applicable to an image forming apparatus provided with a transfer unit for transferring a toner image formed on an image carrying member to a recording medium. Based on the present disclosure, it is possible to provide a transfer unit that can perform, with a simple configuration, switching between two transfer rollers with different lengths in the axial direction and that in addition can suppress a drop in image forming efficiency due to the switching of the transfer roller, and it is also possible to provide an image forming apparatus incorporating such a transfer unit.
Number | Date | Country | Kind |
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JP2021-028360 | Feb 2021 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
20170255133 | Kubota et al. | Sep 2017 | A1 |
20220236666 | Yamada et al. | Jul 2022 | A1 |
20220236667 | Takagi et al. | Jul 2022 | A1 |
20220236669 | Sato et al. | Jul 2022 | A1 |
Number | Date | Country |
---|---|---|
2017-156653 | Sep 2017 | JP |
Number | Date | Country | |
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20220269195 A1 | Aug 2022 | US |