Patent Application
20050105938
The disclosure of Japanese Patent Application No. 2003-345991 filed Oct. 3, 2003 including specification, drawings and claims is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an image forming apparatus and method, wherein a color image or a monochromatic image is formed on an intermediate transfer medium and then, the image on the intermediate transfer medium is secondarily transferred to a recording medium such as a copy sheet, transfer sheet, paper sheet, or transparent sheet for OHP. In this apparatus, the color image is formed by superimposing a plurality of toner images in different colors on top of each other on the intermediate transfer medium such as a transfer belt, a transfer drum or a transfer sheet. Further, the monochromatic image is formed by transferring a monochromatic toner image to the intermediate transfer medium.
2. Description of the Related Art
In the image forming apparatus of this type, an electrostatic latent image is formed by irradiating a light beam on a latent image carrier such as a photosensitive member and a toner image is formed by developing the electrostatic latent image with toner. The toner image thus formed is primarily transferred to the intermediate transfer medium. Subsequently, the toner image is secondarily transferred to the recording medium at a suitable timing. In order to carry out the secondary transfer, a secondary transfer device, such as a secondary transfer roller, is provided being free to abut on or to be cleared from the intermediate transfer medium. And a timing on when the secondary transfer device abuts on the intermediate transfer medium is properly controlled (see, for example, Japanese Unexamined Patent Publication No. 2001-92267).
According to the apparatus disclosed in this Japanese Unexamined Patent Publication No. 2001-92267, a charging process by a charger roller is started at a proper timing and is followed by an exposure process, whereby the electrostatic latent image is formed on the photosensitive member. The electrostatic latent image is developed by a developing device containing a yellow toner, thereby forming a yellow toner image, which is primarily transferred to the intermediate transfer medium. Such an image forming process (exposure process—development process—primary transfer process) is repeatedly performed in the order of yellow, magenta, cyan and black, whereby a color image is formed on the intermediate transfer medium. The color image on the intermediate transfer medium is secondarily transferred to the recording medium by making the secondary transfer roller abut on the intermediate transfer medium in the course of performing the image forming process for the black toner.
The image forming apparatus operative to form the color image in the aforementioned manner is adapted to perform not only a color print mode to form the color image but also a monochromatic print mode to form a monochromatic image by executing the image forming process using the black toner alone. The image forming apparatus performs a secondary transfer process by making the secondary transfer roller abut on the intermediate transfer medium at a predetermined timing regardless of whether the operation is in the color print mode or in the monochromatic print mode. Therefore, the apparatus can only provide a control suited for either one of the color print mode and the monochromatic print mode. Hence, there still exists some points to be improved in this respect.
A primary object of the present invention is that in the image forming apparatus and method capable of selectively executing the color print mode and the monochromatic print mode, a timing on when the secondary transfer device abuts on the intermediate transfer medium is optimized in both of the print modes.
According to an aspect of the present invention, there is provided an image forming apparatus, comprising: a toner image forming section which performs an image forming process in which a toner image is formed by developing a latent image by means of one of plural developing devices that is selected to move to a predetermined development position, the plural developing devices containing toner of which toner colors different from each other respectively, the latent image formed by irradiating a light beam on a latent image carrier, and the toner image is primarily transferred to an intermediate transfer medium revolving in a fixed direction; a secondary transfer device which is free to be abutting on or cleared from the intermediate transfer medium and which secondarily transfers the toner image on the intermediate transfer medium to a recording medium in abutting on the intermediate transfer medium; and a controller which selectively executes a monochromatic print mode and a color print mode; the monochromatic print mode being a print mode to form a monochromatic image by making the toner image forming section perform the image forming process using toner of a specific color, and to secondarily transfer the monochromatic image to the recording medium by making the secondary transfer device abut on the intermediate transfer medium; the color print mode being a print mode to form a color image by making the toner image forming section perform the image forming process each time one of the plural developing devices is selected to form plural toner images and then superimposing the plural toner images on top of each other on the intermediate transfer medium, and to secondarily transfer the color image to the recording medium by making the secondary transfer device abut on the intermediate transfer medium, wherein a timing on when the secondary transfer device abuts on the intermediate transfer medium in the color print mode is different from the timing in the monochromatic print mode.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention.
The engine EG is provided with a photosensitive member 22 rotatable along a direction of an arrow D1 as seen in
In the photosensitive member cartridge 2 mounted to the main body of the apparatus 1 in the aforementioned manner, an exposure unit 6 irradiates a light beam L onto the outer periphery of the photosensitive member 22 charged by the charger unit 23. The exposure unit 6 irradiates the light beam L on the photosensitive member 22 according to a control command applied from an exposure controller 102 so as to form an electrostatic latent image corresponding to the image signal. When the external apparatus such as a host computer applies the image signal to the CPU 111 of the main controller 11 via an interface (I/F) 112, a CPU 101 of the engine controller 10 outputs a control signal corresponding to the image signal to the exposure controller 102 at a predetermined timing. In response to the control signal, the exposure unit 6 irradiates the light beam L on the photosensitive member 22 so that the electrostatic latent image corresponding to the image signal is formed on the photosensitive member 22. Thus, according to the preferred embodiment, the photosensitive member 22 corresponds to a “latent image carrier” of the present invention.
The electrostatic latent image thus formed is developed into a toner image by means of the developing unit 4. In this embodiment, the developing unit 4 includes a support frame 40 adapted to rotate about an axis, a yellow developing device 4Y, a magenta developing device 4M, a cyan developing device 4C and a black developing device 4K. These developing devices 4Y, 4C, 4M, 4K are each designed to be removably mounted to the support frame 40 and each contain toner of respective color.
Based on a control command from a developing device controller 104 in the engine controller 10, the developing unit 4 is driven into rotation and when one of the developing devices 4Y, 4C, 4M, 4K is selectively positioned at a predetermined development position abutting against the photosensitive member 22 or facing the photosensitive member 22 via a predetermined gap therebetween, one of developing rollers 41Y, 41C, 41M, 41K of the developer positioned at the development position carrying thereon toner of selected color supplies the toner to the photosensitive member 22. Thus, the electrostatic latent image on the photosensitive member 22 is developed in a selected toner color.
The toner image developed by the developing unit 4 in the aforementioned manner is primarily transferred onto an intermediate transfer belt 71 of a transfer unit 7 in a primary transfer region TR1. The transfer unit 7 includes the intermediate transfer belt 71 entrained about a plurality of rollers 72-75, and a driver (not shown) operative to drive the roller 73 into rotation thereby driving the intermediate transfer belt 71 in revolution in a predetermined moving direction D2.
A transfer belt cleaner (not shown) and a vertical synchronous sensor 77 are disposed near the roller 75. The vertical synchronous sensor 77 is to detect a reference position of the intermediate transfer belt 71 and functions as a vertical synchronous sensor which acquires a synchronous signal outputted in relation to a revolution in sub scanning direction of the intermediate transfer belt 71, the synchronous signal being a vertical synchronous signal Vsync. In this apparatus, the operation of the individual parts is controlled based on the vertical synchronous signal Vsync for synchronizing the operation timing of the individual sections and for superposing the toner images of each color correctly. That is, the individual parts of the engine EG operate in synchronization with the vertical synchronous signal whereby an image forming process is carried out. The “image forming process” means a process to form the toner image by developing the latent image on the photosensitive member 22 by means of one of the developing devices 4Y, 4M, 4C, 4K that is selected to move to the development position and to transfer the toner image onto the intermediate transfer belt 71 that moves in the fixed moving direction D2. Thus, the image forming process is performed each time one of the developing devices 4Y, 4M, 4C, 4K is selected and toner images of four colors are superimposed on top of each other on the intermediate transfer belt 71 whereby a color image is formed (color print mode). The color image is formed in this manner and is secondarily transferred to the recording medium S taken out from a cassette 8 one by one and transported along a transportation path F to a secondary transfer region TR2.
In a case where a monochromatic image is secondarily transferred to the recording medium S, on the other hand, the monochromatic image is formed by performing the image forming process for black color (monochromatic print mode). Subsequently, the same procedure as that for the color image is taken to transfer the resultant monochromatic image to the recording medium S transported to the secondary transfer region TR2. Thus is obtained a print of the monochromatic image.
In this performance, a timing on when to feed the recording medium S to the secondary transfer region TR2 is controlled in order to ensure that the image on the intermediate transfer belt 71 is transferred exactly to a predetermined place on the recording medium S. Specifically, a gate roller 81 is provided on the transportation path F at a place upstream from the secondary transfer region TR2. The gate roller 81 is rotated in exact timing to the revolution of the intermediate transfer belt 71, thereby feeding the recording medium S to the secondary transfer region TR2 at a predetermined timing.
Referring back to
In
(a) Color Print Mode
When the aforesaid color print command is applied from the external apparatus, the main controller 11 converts the color print command into job data in a format suited for directing the operations of the engine EG and then, sends the job data to the engine controller 10. The engine controller 10, in turn, controls the individual parts of the engine EG based on the job data sent from the CPU 111, so that a color image is formed on the intermediate transfer belt 71. Specifically, the color image is formed by performing: (a-1) an image forming process to form a black toner image; (a-2) an image forming process to form a cyan toner image; (a-3) an image forming process to form a magenta toner image; and (a-4) an image forming process to form a yellow toner image.
(a-1) Image Forming Process to Form Black Toner Image
In this process, the black developing device 4K is selected to move to the development position. Further, an electrostatic latent image for black color is formed on the photosensitive member 22 and then is developed by the developing device 4K thereby forming a toner image, which is transferred onto the intermediate transfer belt 71 moving in the moving direction D2. Thus, the black toner image is carried on the intermediate transfer belt 71. In the latter half of this image forming process, movement of a switch to the developing device 4C of the next toner color is started.
(a-2) Image Forming Process to Form Cyan Toner Image
When the cyan developing device 4C is selected to move to the development position, the rotational driving of the developing unit 4 stops. Further, an electrostatic latent image for cyan color is formed on the photosensitive member 22 and then is developed by the developing device 4C thereby forming a toner image, which is transferred onto the intermediate transfer belt 71 in a manner to be superimposed on the black toner image formed in the preceding process (a-1). In the latter half of this image forming process, movement of a switch to the developing device 4M of the next toner color is started.
(a-3) Image Forming Process to Form Magenta Toner Image
When the magenta developing device 4M is moved to the development position, the rotational driving of the developing unit 4 is stopped. Further, an electrostatic latent image for magenta color is formed on the photosensitive member 22 and then is developed by the developing device 4M thereby forming a toner image, which is transferred onto the intermediate transfer belt 71 in a manner to be superimposed on the toner images formed in the preceding processes (a-1), (a-2). In the latter half of this image forming process, movement of a switch to the developing device 4Y of the next toner color is started.
(a-4) Image Forming Process to Form Yellow Toner Image
When the yellow developing device 4Y is moved to the development position, the rotational driving of the developing unit 4 is stopped. Further, the light beam L is irradiated on the photosensitive member 22 at a predetermined exposure start time T1, so as to form an electrostatic latent image corresponding to an image signal Y The resultant latent image is developed by the developing device 4Y thereby forming a toner image, which is transferred onto the intermediate transfer belt 71 in a manner to be superimposed on the toner images formed in the preceding processes (a-1) through (a-3). These four image forming processes are repeated so as to superimpose the toner images of the four colors on top of each other on the intermediate transfer belt 71, whereby the color image is formed.
(a-5) Secondary Transfer Process
In the color print mode, the secondary transfer roller 78 is positioned at a separating position (indicated by a broken line in
According to the preferred embodiment, the secondary transfer roller 78 is moved to the intermediate transfer belt 71 to abut on the intermediate transfer belt 71 in the course of performing the last image forming process (a-4), in other words, in the course of irradiating the light beam on the photosensitive member 22. Therefore, it is impossible to eliminate the adverse effect of the abutting of the secondary transfer roller 78 on the intermediate transfer belt 71 completely.
The “effect of the abutting of the secondary transfer roller 78 (secondary transfer device) on the intermediate transfer belt 71 (intermediate transfer medium)” includes displacement of an exposure position of the light beam (hereinafter, referred to as “banding”). The followings are thought to be causative factors of the banding. When the secondary transfer roller 78 abuts on the intermediate transfer belt 71, for example, load on the intermediate transfer belt 71 is varied so that the moving speed of the intermediate transfer belt 71 is varied. The varied moving speed of the intermediate transfer belt 71 affects the photosensitive member 22 (latent image carrier) via the primary transfer region TR1 where the primary transfer of the toner image is carried out. Thus, the moving speed of the photosensitive member 22 is also varied.
Furthermore, when the secondary transfer roller 78 abuts on the intermediate transfer belt 71, a frame retaining individual parts of the apparatus encounters vibrations, which may affect to vary the moving speed of the photosensitive member 22. Thus, if the secondary transfer roller 78 abuts on the intermediate transfer belt 71 during the irradiation of the light beam (exposure process) to cause the variation of the moving speed of the photosensitive member 22, the banding occurs.
As described above, according to the preferred embodiment, the secondary transfer roller 78 abuts on the intermediate transfer belt 71 in the course of irradiating the light beam on the photosensitive member 22. Therefore, it is impossible to eliminate the adverse effect of the banding completely. On this account, the embodiment specifies the yellow toner as the toner to be used in the last image forming process (a-4), the yellow toner the least perceptible to the human eyes among the four toner colors (Y, M, C, K). Thus, the adverse effect of the banding may be minimized even if a part of the yellow toner image should suffer density variations because of the banding.
(b) Monochromatic Print Mode
When the aforesaid monochromatic print command is applied from the external apparatus, the main controller 11 converts the monochromatic print command into job data in a format suited for directing the operations of the engine EG and then, sends the job data to the engine controller 10. The engine controller 10, in turn, controls the individual parts of the engine EG based on the job data sent from the CPU 111, so that a monochromatic image is formed on the intermediate transfer belt 71. Specifically, with the black developing device 4K moved to the development position, an image forming process to be described below is repeated five times for successively forming five monochromatic images.
Each of the image forming processes forms a single monochromatic image. More specifically, the image forming process of the first time is performed the same way as the aforementioned image forming process (a-1) so as to form a monochromatic image. That is, an electrostatic latent image for black color is formed on the photosensitive member 22 and then is developed by the developing device 4K thereby forming a toner image, which is transferred to the intermediate transfer belt 71 moving in the moving direction D2. Thus, the black toner image is formed as the first monochromatic image on the intermediate transfer belt 71. The subsequent image forming processes are performed the same way, thereby forming monochromatic images, respectively.
According to the embodiment, the timing on when the secondary transfer roller 78 abuts on the intermediate transfer belt 71 is different from the timing in the color print mode (a). Namely, in the monochromatic print mode, as shown in
According to the preferred embodiment, as described above, the image forming apparatus capable of selectively executing the color print mode and the monochromatic print mode is arranged such that the timing on when the secondary transfer device abuts on the intermediate transfer medium is varied depending upon the print mode. Hence, the apparatus is capable of making the secondary transfer roller 78 abut on the intermediate transfer belt 71 at an abutting time suited for each print mode. Accordingly, the effect of the abutting of the secondary transfer roller 78 on the intermediate transfer belt 71 may be optimized in each print mode, thereby ensuring that a good image is formed.
According to the preferred embodiment, in particular, the secondary transfer roller 78 is disposed such that a tangential direction of the trajectory 793 is oriented downward with respect to a rotational center of the roller 73 when the secondary transfer roller 78 abuts on the intermediate transfer belt 71. Thus, the embodiment adopts an arrangement in which the roller 73 is moved upward when the secondary transfer roller 78 abuts on the intermediate transfer belt 71, so that the intermediate transfer belt 71 is prone to speed variations. Hence, a significant merit is afforded by adopting the arrangement of the present invention.
It is to be noted that the invention is not limited to the foregoing embodiment and various other changes than the above may be made so long as such changes do not depart from the scope of the present invention. For example, while a plurality of images are successively printed in the foregoing embodiment, it goes without saying that a similar effect may be obtained in a case where the printing operation is performed one by one. Further, while the foregoing embodiment forms a single image on the intermediate transfer belt 71, the present invention is also applicable to an image forming apparatus adapted to form a plurality of images on the intermediate transfer belt 71.
Further, although the foregoing embodiment employs the intermediate transfer belt 71 as the intermediate transfer medium, the intermediate transfer medium is not limited to this. The present invention is also applicable to an image forming apparatus which employs, for example, an intermediate transfer drum or intermediate transfer sheet as the intermediate transfer medium.
Further, although the foregoing embodiment employs the secondary transfer roller 78 as the secondary transfer device, the secondary transfer device is not limited to this. The present invention is also applicable to an image forming apparatus which employs, for example, a belt-type secondary transfer device.
Further, while the foregoing embodiment adopts the rotary drive system for selectively moving any one of the four developing devices 4Y, 4M, 4C, 4K to the predetermined development position, the number of developing devices is not limited to “four”. The present invention may be applied to all kinds of image forming apparatuses adapted for the movement of two or more developing devices. Furthermore, the drive system of the developing unit is not limited to the rotary system. The present invention is also applicable to an image forming apparatus in which the movement of the developing devices is accomplished by selectively transporting any one of the developing devices to the development position.
Further, in the foregoing embodiment, the monochromatic image is formed using the black toner specified as the toner of a “specific color” of the present invention. However, the present invention is also applicable to an image forming apparatus in which a monochromatic image is formed using toner of another color specified as the “specific color” of the present invention. Furthermore, the image forming apparatus includes all types of image forming apparatuses such as copiers and facsimile machines.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as other embodiments of the present invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-345991 | Oct 2003 | JP | national |
