Patent Grant
8055170
1. Field of the Invention
The present invention relates to an image forming apparatus in which a toner image is transferred onto a sheet with use of an intermediate transferring belt.
2. Description of the Related Art
A conventional technology related to this kind of image forming apparatus has been a technology disclosed in, for example, Japanese Patent Unexamined Publication H11-288188 (referred to as a patent document 1, hereinafter). The patent document 1 discloses image forming of primarily transferring a toner image onto an intermediate transferring belt and then secondarily transferring the toner image onto a sheet. According to the patent document 1, an electrostatic latent image is formed on a surface of a photoconductive member based on image data, and the latent image is developed by a multi-color developing device for each color and primarily transferred to the intermediate transferring belt. Then, the toner images of all colors are synthesized into one color toner image, and then the color toner image is secondarily transferred from the intermediate transferring belt onto a sheet.
Further, according to the patent document 1, there is provided a guide plate at an upstream position of the transferring roller for guiding the sheet along the surface of the intermediate transferring belt. A sheet sent from a pair of registration rollers is guided by the guide plate and conveyed in a direction along the surface of the intermediate transferring belt. The guide plate ends at an upstream position upstream of the transferring roller, and the sheet is taken over by a guide of another member (a member which is integrally formed with a holder of the transferring roller) from the end (downstream) of the guide plate. Then, the sheet is guided by the guide and sent to a nip portion between the intermediate transferring belt and the transferring roller, and then the toner image is secondarily transferred onto the sheet while the sheet passes through the nip portion.
The intermediate transferring belt used in the above-described patent document 1 is normally driven (rotationally running) in a state where a tension is given to some extent. Therefore, it is likely that an oscillation (movement) with a flexure in a thickness direction on a rotational path of the belt. Such flexural oscillation of the intermediate transferring belt changes a distance between the sheet and the intermediate transferring belt in an area immediately before a nip portion between the transferring roller and the intermediate transferring belt (an upstream position in the conveying direction).
On the other hand, in the case where a sheet is conveyed in a direction along a surface of the intermediate transferring belt like the patent document 1, the sheet and the intermediate transferring belt are extremely close to each other immediately before the nip portion. At this time, if a distance between the intermediate transferring belt and the sheet becomes so small because of deformation of the intermediate transferring belt, the sheet may rub a toner image on the belt before it enters the nip portion, and a part of the toner image stuck to the belt may be dispersed on the sheet. In particular, since a rear end portion of a sheet can be freely moved after the rear end of the sheet goes out from the nip portion of the pair of registration rollers, the intermediate transferring belt is likely to come in contact with the sheet if the sheet slightly hops when the flexure occurs in the intermediate transferring belt. In this case, even if a toner image is correctly formed, a quality of an image outputted after the secondary transfer is negatively affected.
In view of the above, an object of the present invention is to get rid of an effect to an image quality due to a flexure which occurs in an intermediate transferring belt to output a high-quality image.
In order to achieve the above-described object, an image forming apparatus according to the present invention comprises: an image forming unit for forming a toner image by developing a latent image formed on an image bearing member with toners; an intermediate transferring belt which runs in a state where the toner image formed by the image forming unit is transferred onto its surface; a transferring roller which is arranged close to the surface of the intermediate transferring belt; a sheet conveying section for conveying a sheet through a conveying path along the surface of the intermediate transferring belt and allowing the toner image to transfer onto a transfer surface of the sheet through a nip portion formed between the intermediate transferring belt and the transferring roller; and a clearance retaining section for guiding the sheet along a conveying surface provided at an upstream position of the transfer nip portion in the conveying path and retaining a clearance between the conveying surface and the intermediate transferring belt to be greater than a predetermined clearance.
Accordingly, even if flexural oscillation occurs in the intermediate transferring belt, the surface of the intermediate transferring belt does not come too close to the sheet conveyed on the conveying surface. Therefore, it can prevent rubbing of the sheet with respect to a surface of the transferring belt at an upstream position of the transfer nip portion and spreading of toners on the sheet.
These and other objects, features and advantages of the present invention will become apparent upon reading of the following detailed description along with the accompanied drawings.
Hereinafter, a first embodiment of an image forming apparatus will be described.
The image forming apparatus 1 includes an image forming section 2 in its main body. The image forming section 2 mainly has a photoconductive drum 4, a charging device 6, a laser scanning unit 8 and a developing unit 10.
The photoconductive drum 4 has a main body which includes a drum-like member of a rotation type, and a photoconductive member layer of, for example, an amorphous silicon is formed on an outer peripheral surface of the photoconductive drum 4. The photoconductive drum 4 is rotated in a counter-clockwise direction in
In a periphery of the photoconductive drum 4, the charging device 6 is provided close to an upper position of the photoconductive drum 4. The charging device 6 charges the outer peripheral surface of the photoconductive drum 4. In a state where the photoconductive drum 4 is charged, a scanning light as an image signal is irradiated from the laser scanning unit 8 toward the outer peripheral surface. At this time, a position to which the scanning light is irradiated is at downstream of the charging device 6 in a rotational direction of the photoconductive drum 4.
The laser scanning unit 8 reflects the laser light while rotating, for example, a polygon mirror at a high speed, and reflects on a flat mirror the laser light (scanning light) scanned in an axial direction of the photoconductive drum 4 to allow the outer peripheral surface of the photoconductive drum 4 to be exposed to the laser light. This allows an electrostatic latent image to be formed on the outer peripheral surface of the photoconductive drum 4.
The developing unit 10 is arranged closely to the outer peripheral surface of the photoconductive drum 4 on downstream of the irradiating position of the scanning light in the rotational direction of the photoconductive drum 4. The developing unit 10 develops an electrostatic latent image in a rotary method with use of toners of four colors (for example, magenta, cyan, yellow, black). Therefore, the developing unit 10 is also configured as to be rotatable and has four developing equipments 10a, 10b, 10c, 10d which are sectionalized for respective colors in a rotational direction. Each of the developing equipments 10a through 10d accommodates toners. Further, the developing equipments 10a through 10d have developing rollers 11a through 11d, respectively, each of which rotates while bearing toners on a respective outer peripheral surface.
Further, a toner container 9 is provided in the image forming apparatus 1, and toners for respective colors are supplied to the developing equipments 10a through 10d through a feed pipe 13. In the present embodiment, an unillustrated toner amount sensor detects toner amount of each of the developing equipments 10a through 10d, and toners are fed to retain a constant toner amount.
The developing unit 10 of a rotary type rotates and stops in such a manner that one of the developing equipments 10a through 10d which corresponds to a color to be developed faces the outer peripheral surface of the photoconductive drum 4. In a corresponding one of the developing equipments 10a through 10d, a respective one of the developing rollers 11a through 11d rotates while bearing a thin layer of toners on its outer peripheral surface, and a developing bias voltage including an AC-component and a DC-component is applied to one of the developing rollers 11a through 11d. This developing bias allows toners bore on the developing rollers 11a through 11d to be moved to an electrostatic latent image formed on the photoconductive drum 4 so that the electrostatic latent image is developed with toners of respective colors, and then a toner image as a visible image is formed on the outer peripheral surface of the photoconductive drum 4.
At a position under the photoconductive drum 4, an endless intermediate transferring belt 12 is arranged. The intermediate transferring belt 12 may be configured by, for example, a belt which is formed by superimposing and joining respective end portions of sheet members made of a dielectric resin, or a belt having no joints (seamless). The intermediate transferring belt 12 passes through a position in contact with the outer peripheral surface and runs in a rotational direction while being in synchronization with rotation of the photoconductive drum 4. The toner image formed on the photoconductive drum 4 is primarily transferred from the outer peripheral surface to the surface of the intermediate transferring belt 12 in accordance with rotation of the photoconductive drum 4.
In a periphery of the photoconductive drum 4, a slide-rubbing member 14 and a cleaning member 16 are arranged along the outer peripheral surface. The slide-rubbing member 14 and the cleaning member 16 are positioned on downstream of a position where the photoconductive drum 4 is in contact with the intermediate transferring belt 12 and on upstream of the charging device 6 in a rotational direction of the photoconductive drum 4. The slide-rubbing member 14 polishes the outer peripheral surface of the photoconductive drum 4 onto which the toner image is primarily transferred, so that an oxidized product attached to a layer of an amorphous silicon photoconductive member is removed. Further, the cleaning member 16 removes toners remaining on the outer peripheral surface of the photoconductive drum 4 and cleans the outer peripheral surface before next image forming is performed.
At a time of forming a full color image, electrostatic latent images for respective colors are formed on the photoconductive drum 4, and toner images developed by the developing unit 10 for respective colors are primarily transferred onto the intermediate transferring belt 12 in superimposition with each other, so that a color image for one page is synthesized.
The intermediate transferring belt 12 is wound around a driving roller 18a and a tension roller 12a, and a primary transfer position close to the photoconductive drum 4 is provided therebetween. The driving roller 18a is arranged en-upstream of the primary transfer position in a rotational direction of the intermediate transferring belt 12, and the tension roller 12a is arranged en-downstream. Further, the tension roller 12a applies an appropriate amount of tension to the intermediate transferring belt 12 with use of a repulsive force of, for example, an unillustrated spring.
At one end portion of the intermediate transferring belt 12, a transferring section 18 is provided. The transferring section 18 is provided with a transferring roller 18b. The transferring roller 18b is rotated in pair with the above-described driving roller 18a over the intermediate transferring belt 12. Therefore, in the transferring section 18, there is formed a transfer nip portion between the intermediate transferring belt 12 and the transferring roller 18b. A sheet passes through the transfer nip portion, so that a full-color toner image for one page is secondarily transferred from the intermediate transferring belt 12 to the sheet.
In a case of forming images on both sides of a sheet, a part of the sheet which passes through the fixing section 20 once projects outward from the apparatus through the sheet-discharging roller 21. Thereafter, the sheet is taken into the apparatus again by a reverse rotation of the sheet-discharging roller 21, and then conveyed to the front surface side through a sheet reversing passage 23. Then, the sheet is conveyed to the transferring section 18 again, and a toner image corresponding to the other surface is secondarily transferred to the sheet. Thereafter, the toner image is fixed on the other surface of the sheet at the fixing section 20, and then discharged to the sheet-discharging tray 22.
The sheet onto which the toner image is transferred is accommodated in the sheet-supplying cassette 24 in a lower portion of the apparatus in a stacked state. The sheet is taken one after another from an upper most position of the stack and then conveyed to the transferring section 18 through the sheet-feeding roller 26 and the registration roller 28. The registration roller 28 once stops in a state of retaining the sheet, corrects inclination and skew of the sheet, and then sends out the sheet at a timing in synchronization with running of the intermediate transferring belt 12. This allows the toner image for one page to be accurately transferred to a prescribed position of the sheet. There is provided a cleaning unit 29 near the transferring section 18, and the cleaning unit 29 removes remaining toners attached to the intermediate transferring belt 12 after the toner image is transferred.
The basic configuration of the image forming apparatus 1 and its image forming operation are described above. In
The image input section 30 is configured as a receiving section for receiving image data (a group of image data for all pages) transmitted from, for example, an personal computer. In a case where the image forming apparatus 1 is a copying machine or a complex machine, the image input section 30 is configured by a scanning optical system which includes a scanner lamp for illuminating a document at a time of copying and a mirror for changing a light path of a light reflected from a document, a collective lens for collecting the reflected light from the document and forming an image, and a CCD for converting the formed image light to an electric signal. The image signal inputted to the image input section 30 is applied with a signal processing (P/S conversion, A/D conversion, or the like) when necessary, and thereafter transferred to an image memory 40 in the storage section 33.
The storage section 33 is provided with the image memory 40, a RAM 41, and a ROM 42. Among those, the image memory 40 is a buffer which is adapted to store an image signal transferred from the image input section 30 and transfer the same to the controller 32. The RAM 41 and the ROM 42 stores a processing program and a processing content of the control section, and further stores a set value and the like for a developing bias applied to the developing unit 10.
The operation panel 34 includes an operating section having a plurality of operation keys and a display portion for displaying settings and a status of the apparatus (any of those are not shown). It is favorable that a display portion be a liquid crystal display, and the display portion may be a touch panel which receives an operation through its display screen. Such operation panel 34 is provided on an exterior cover surface of the image forming apparatus 1 to receive settings such as a print setting inputted by a user through the operation keys. Further, for example, in a case where the image forming apparatus 1 has a facsimile function, the operation panel 34 may be used for registering facsimile addressees to the storage section 33, and further used for conducting various settings such reading and re-writing the registered addressees.
Driving sections including the photoconductive drum 4, the developing unit 10, the intermediate transferring belt 12, the transferring roller 18b, and the fixing section 20 are driven by a main motor which is not illustrated. The controller 32 has a function of controlling rotation of the main motor to allow the various driving portions to be operated appropriately. In a case of driving or stopping only any one of the driving portions, a clutch mechanism (not shown) provided between the main motor and a respective driving portion is connected or disconnected. It may be so configured that a motor for exclusive use is connected to each of the driving portions so that each unit is driven independently from other units.
Further, the controller 32 is connected with an image density sensor 15 (not shown in
Furthermore, the controller 32 is connected with a drive motor (not shown) for performing feeding of a sheet and conveying and discharging of a sheet onto which an image is transferred, and the controller 32 sends a control signal to the drive motor. The controller 32 controls a rotational state of the drive motor, so that respective rotations of the sheet-feeding roller 26, the registration roller 28, and the sheet-discharging roller 21 (not shown in
Furthermore, the controller 32 generally controls the image input section 30, the image forming section 2, and the fixing section 20 in accordance with a set program, and it converts an image signal inputted from the image input section 30 to image data and executes a magnification processing or a gradation processing when necessary. The converted image data includes four image signals for respective colors of magenta, cyan, yellow, and black to form a color image. The image signal for respective colors are transmitted in a certain order to a laser scanning unit 8 of the image forming section 2. The laser scanning unit 8 generates a pulse laser light in accordance with the image signal transmitted from the controller 32 and irradiates the pulse laser light to the outer peripheral surface of the photoconductive drum 4 while reflecting the same on a polygon mirror.
On the other hand, the image forming section 2 sends synchronizing signals individually (for respective colors) to the controller 32. The synchronizing signals are used for synchronizing timings that the controller 32 transmits image signals for respective colors. When developing of an image is performed by each of the developing equipments 10a through 10d in the developing unit 10, the synchronizing signals are sent sequentially from an image forming controller. Then, when the controller 32 receives synchronizing signals for respective colors, image signals for respective colors are transmitted to the image forming section in the order of reception.
The image forming control executed in the image forming apparatus 1 is generally described above. In accordance with the image forming control of the present embodiment, forming of a high-quality toner image is performed based on image data. However, even if an appropriate control is performed to form a toner image, a belt surface may be rubbed with a sheet to affect a quality of an outputted image as described above when a flexural oscillation (movement) occurs in the intermediate transferring belt 12 immediately before a transfer nip portion of the transferring section 18. Therefore, in the present embodiment, the following configuration is applied to maintain a high quality image.
In the present embodiment, a pre-transfer guide 50 (guide member) according to a first embodiment is provided immediately before a transfer nip portion between the intermediate transferring belt 12 and the transferring roller 18b, so that a distance (clearance) between the intermediate transferring belt 12 and a sheet (identified by a reference sign P) conveying is retained to be greater than a predetermined amount at a position immediately before the transfer nip portion. Hereinafter, the pre-transfer guide 50 according to the first embodiment will be described in detail.
As shown in
In a lower portion of the pre-transfer guide 50, four hooking claws 50c are formed in a longitudinal direction at intervals. Each of the hooking claws 50c has a base end portion which slightly hangs downwardly from the pre-transfer guide 50 and bends in a longitudinal direction toward a leading end, so that it has an L-shape. The pre-transfer guide 50 is detachably supported by hooking the hooking claws 50c to the conveying unit 52.
In a part of the conveying unit 52, there is formed a plate-like supporting plate 54. The supporting plate 54 extends in a width direction of the conveying path like the pre-transfer guide 50, and its upper surface is so formed as to be a flat surface. Further, in the supporting plate 54, there are formed four hooking holes 56 which are open on the upper surface. The hooking holes 56 are formed through the supporting plate 54 in a thickness direction, and each of those has a shape which is elongated in a width direction of the conveying path when viewed from the upper surface.
Next,
As shown in
Next, as shown in
Then, as shown in
Further, for example, in the case of replacing the pre-transfer guide 50 as a wear-out part, the pre-transfer guide 50 can be detached in the reverse procedure. The supporting plate 54 and the hooking claws 50c should be referred to
Next, a function of the intermediate transferring belt 12 will be described in detail.
Even in this case, since the projections 50b of the pre-transfer guide 50 are formed on the outer side of the area on which the sheet is conveyed as shown in
According to the pre-transfer guide 150 of the second embodiment, when the intermediate transferring belt 12 bows downward greatly, and its surface comes in contact with the guide roller 152, the guide roller 152 is rotated by running of the intermediate transferring belt 12. This softens a friction with respect to the intermediate transferring belt 12.
The present invention is not limited to the first embodiment described above, and it may be changed variously and practiced.
In the pre-transfer guides 50, 150 of the first and second embodiments, the projections 50b or the guide rollers 152 are provided on opposite sides of the conveying surface 50a. However, it may be provided only on one side. Alternatively, the projection 50b shown in the first embodiment may be provided on one side, and the guide roller 152 may be provided on the other side.
In the first embodiment, an example is shown where an angle between the sheet conveying path and the intermediate transferring belt 12 is relatively small. However, for example, the present invention may be applied to the configuration where the sheet conveying path extends in a lengthwise direction and the intermediate transferring belt extends in a widthwise direction.
In the first embodiment, the developing unit of a rotary type is shown as an example. However, a developing unit may be of a tandem type. Further, an image forming apparatus of a full-color type is shown in the first embodiment. However, the image forming apparatus may be of a monochromatic type.
In summary, an image forming apparatus according to the present invention has a configuration of primarily transferring a toner formed by the image forming unit to the intermediate transferring belt and secondarily transferring the toner image from the intermediate transferring belt to a sheet. The image forming unit is adapted to form a toner image by developing a latent image formed on an image bearing member with toners. The intermediate transferring belt runs in a state where the toner image formed by the image forming unit is transferred on its surface.
A transferring roller is arranged close to the surface of the intermediate transferring belt, and a transfer nip portion is formed between the transferring roller and the intermediate transferring belt. The sheet is conveyed through a conveying path along the surface of the intermediate transferring belt, and passes through the transfer nip so that the toner image is secondarily transferred on the sheet.
In particular, the present invention is provided with a function of retaining a clearance between a conveying surface, which is adapted to guide a sheet at an upstream position before a sheet conveyed through the conveying path reaches the transfer nip portion, and the surface of the intermediate transferring belt to be greater than a predetermined clearance. This prevents the surface of the intermediate transferring belt from coming too close to the sheet guided on the conveying surface even if a flexural oscillation occurs in the intermediate transferring belt, so that rubbing of a sheet with respect to the surface of the transfer belt at an upstream position of the transfer nip and dispersing of toners on the sheet can be prevented.
As a configuration for realizing the function of retaining the clearance to be greater than the predetermined clearance as described above, the present invention is provided with a projection on an outer side of a passing area of the sheet in a width direction of the conveying path. This projection is so configured as to project toward the surface of the intermediate transferring belt from the conveying surface of the conveying path.
In this case, a clearance between the conveying surface and the surface of the intermediate transferring belt can be retained to be greater than a predetermined clearance through the above-described projection, so that a contact between the conveying surface and the surface of the intermediate transferring belt can be prevented by the projection even if the flexure causes the surface of the intermediate transferring belt to come close to the sheet on the conveying surface.
Alternatively, as a more practical configuration, a guide member is provided at an upstream position of the transfer nip portion in the sheet conveying. This guide member has a conveying surface which extends in a width direction of the conveying path at an upstream position of the transfer nip portion to guide the sheet along the conveying surface. The guide member is integrally formed with the above-described projection. In this case, the projection is so configured as to project toward a surface of the intermediate transferring belt from the conveying surface at a position outer than a sheet passing area on the conveying surface.
In this case, the guide member can retain the clearance between the conveying surface and the surface of the intermediate transferring belt to be greater than a predetermined clearance through the projection, so that a contact between the surfaces can be prevented by the projection even if the flexure causes the surface of the intermediate transferring belt to come close to the sheet on the conveying surface.
Further, the present invention may be further provided with an attaching and detaching structure for detachably supporting the guide member with respect to the conveying path. In this case, even if the guide member is used up due to abrasion or the like, it can be easily replaced.
Further, according to the present invention, a guide roller can be used in place of the above-described projection. The guide roller is provided on an outer side of a passage area of the sheet in a width direction of the conveying path and rotatably supported at such a position that the summit of the circumference surface of the guide roller is closer to the surface of the intermediate transferring belt than the conveying path (conveying surface). Further, the guide roller may be provided on the guide member in place of the above-described projection.
In this case, a clearance between the conveying surface and the surface of the intermediate transferring belt can be retained to be greater than a predetermined clearance through the guide roller, so that a contact between the sheet on the conveying surface and the intermediate transferring belt can be assuredly prevented. Further, even if the peripheral surface of the guide roller comes in contact with the surface of the intermediate transferring belt, the guide roller is drivenly rotated by running of the intermediate transferring belt, so that abrasion of the belt can be reduced.
According to the present invention, a distance between the sheet and the surface of the intermediate transferring belt can be retained to be greater than a predetermined distance regardless of changes in a state of conveying the sheet and largeness of flexure on a rotational path of the intermediate transferring belt. Accordingly, rubbing of a sheet with respect to toner image formed on the intermediate transferring belt before the secondary transfer and dispersing of the toner image on the belt to the sheet are prevented, so that a stable and high-quality image can be transferred onto the sheet.
This application is based on Japanese Patent Application Serial No. 2007-066374 filed in Japan Patent Office on Mar. 15, 2007, the contents of which are hereby incorporated by reference.
Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-066374 | Mar 2007 | JP | national |
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| 7424257 | Yoo et al. | Sep 2008 | B2 |
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| 20070025786 | Yasuhara et al. | Feb 2007 | A1 |
| Number | Date | Country |
|---|---|---|
| 11-288188 | Oct 1999 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20080226362 A1 | Sep 2008 | US |
