The present document incorporates by reference the entire contents of Japanese priority document, 2005-265663 filed in Japan on Sep. 13, 2005.
1. Field of the Invention
The present invention relates to a technology for superimposing a plurality of different single-color images to obtain a color image.
2. Description of the Related Art
An image forming apparatus, in which a latent image is written on a photoconductor serving as an image carrier by an optical beam such as a laser beam, visualized by a developing device, and transferred onto a recording medium such as transfer paper, is widely used for a copier, a printer, a facsimile machine, a multifunction product, and the like. A color image forming apparatus capable of color image processing is in widespread use in response to growing market demand. As the color image forming apparatus, a so-called tandem type color image forming apparatus is widely used because high-speed image forming can be easily achieved. In the tandem type color image forming apparatus, a plurality of photoconductors each including a developing device are arranged in parallel, and single-color toner images formed on the respective photoconductors are sequentially transferred onto transfer paper to form a full-color image thereon.
In the color image forming apparatus, at the time of superimposing colors, color unevenness sometimes occurs in an image due to deviation of a color-superimposing position from a target position. Such a deviation is caused by, for example, rotational fluctuation generated cyclically for each one rotation of the photoconductors. The rotational fluctuation is corrected by a method in which a rotation detector including four slits is arranged on a shaft of the photoconductor, and a reference clock cycle of a motor serving as a rotation drive source for the photoconductor is adjusted to remove a fluctuation component. However, the rotational fluctuation of the photoconductor cannot be sufficiently removed by the method, thereby causing out-of-color registration.
For example, Japanese Patent Application Laid-Open No. 2002-268315 discloses an imaging device, in which one encoder is coupled with a plurality of photoconductors to detect fluctuations in one rotation of the respective photoconductors to adjust phases of the rotational fluctuation. Japanese Patent Application Laid-Open No. H9-127755 discloses a color image forming device, in which an encoder is attached to a photoconductor for a reference color, and rotational fluctuation of a photoconductor motor is detected based on an output signal from the encoder and deviation between resist marks transferred onto a transfer member as toner images.
In the imaging device, however, because of the belt-coupling, it is difficult to accurately detect fluctuations in one rotation cycle by the encoder due to environmental changes or belt characteristics. In addition, the respective photoconductors are coupled with one encoder, and therefore, the mechanism is complicated and large.
In the color image forming device, rotational fluctuation of the transfer member appears in between the resist marks of toner images. Therefore, it is difficult to accurately detect fluctuation of the photoconductor. When belt transfer is used, the fluctuation is also affected by belt expansion and contraction.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to an aspect of the present invention, an image forming apparatus includes a plurality of image carriers, a driving unit that rotationally drives the image carriers in an individual manner, and a phase adjusting unit that adjusts, based on a reference rotation position on one of the image carriers, phase of rotational fluctuation of the other image carrier per one rotation.
According to another aspect of the present invention, a method for controlling an image forming apparatus, includes rotationally-driving a plurality of image carriers in an individual manner, setting a reference rotation position on one of the image carriers, and adjusting, based on the reference rotation position, phase of rotational fluctuation of the other image carrier per one rotation.
According to still another aspect of the present invention, an image forming apparatus includes a plurality of image carrier means, driving means for rotationally driving the image carrier means in an individual manner, and phase adjusting means for adjusting, based on a reference rotation position on one of the image carrier means, phase of rotational fluctuation of the other image carrier means per one rotation.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments of the present invention will be explained below. In the following description, like reference numerals or letters refer to corresponding parts throughout the drawings, and the similar description is not repeated.
After being evenly charged by the charger 6, a surface of the photosensitive drum 1Y is exposed with a laser beam corresponding to a yellow image by the laser write unit 9 to be formed with an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 2Y, so that a toner image is formed on the photosensitive drum 1Y. The toner image is transferred onto the intermediate transfer belt 5 at a position (transfer position) in which the photosensitive drum 1Y and the intermediate transfer belt 5 contact with each other by the transfer roller 3Y to form a single-color image of yellow on the intermediate transfer belt 5. After the transfer is finished, unnecessary toner remaining on the surface of the photosensitive drum 1Y is removed by the cleaning device 7 to prepare for a next image formation.
A second image forming unit forms a magenta image on the intermediate transfer belt 5 thus transferred with a single-color (yellow) in a first image forming unit. The second image forming unit also includes a photosensitive drum 1M, a developing device 2M, a transfer roller 3M which is a transfer device, the charger 6, the cleaning device 7, the charge-remover 8, and the laser write unit 9 that are arranged about the photosensitive drum 1M like the first image forming unit. A magenta toner image formed on the photosensitive drum 1M is transferred onto the intermediate transfer belt 5 in superimposition with the yellow image as in the yellow image formation.
Thereafter, toner images formed similarly in a third image forming unit for cyan C and a fourth image forming unit for black B are transferred onto the intermediate transfer belt 5. Thus, a full color image is formed. The third and fourth image forming units have a configuration similar to that of the first and second image forming units. Therefore, a letter representing each color, for example, C for cyan and B for black, is attached to reference numerals denoting respective constituents, and detailed explanation for all these constituents is omitted. When color is not specified, the photosensitive drums and the developing devices are simply represented as photosensitive drums 1 and developing devices 2, respectively. A single-color toner image is formed on each photosensitive drum 1, a composite full-color image is formed by sequentially transferring the single-color toner images on the intermediate transfer belt 5 by contacting the toner images with the intermediate transfer belt 5, and the full-color image is collectively transferred onto a sheet of transfer paper P.
An endless conveyor belt 24 is spanned between a drive roller 27 rotationally driven by a motor 26 and a driven roller 28 on an opposite side of the intermediate transfer belt 5 from the four image forming units. The conveyor belt 24 is arranged to be pressed on the support roller 23 via the intermediate transfer belt 5 so that an image on the intermediate transfer belt 5 is transferred onto transfer paper P on the conveyor belt 24. A registration roller pair 29 rotates in time with the composite color image on the intermediate transfer belt 5 to feed the transfer paper P in between the intermediate transfer belt 5 and the conveyor belt 24.
Besides the tandem type image forming apparatus of the indirect transfer system, a tandem type image forming apparatus of a direct transfer system has been proposed, which directly transfers images on the photosensitive drums 1Y, 1C, 1M, and 1B to the transfer paper P.
Four image forming units for yellow, cyan, magenta, and black are of the same configuration as those in the image forming apparatus of the indirect transfer system described above. A transfer-conveyor belt 30 is spanned between a drive roller 32 and a driven roller 33 below the four image forming units, and rotationally driven in a clockwise direction in
In the tandem type image forming apparatus of the direct transfer system, sheets of transfer paper P are supplied one by one from the registration roller pair 29, and each sheet of transfer paper P is fed onto the transfer-conveyor belt 30 at appropriate timing by a timing roller 15. An image of yellow Y is first formed on the transfer paper P, and images of cyan C, magenta M, and black B are then superimposed on the image of yellow Y.
Besides the image forming apparatuses of the indirect transfer system and the direct transfer system described above, a tandem type image forming apparatus of another system has been proposed, in which the intermediate transfer member is divided into two members.
In the image forming apparatus of this system, four image forming units for yellow, cyan, magenta, and black are also of the same configuration as those in the image forming apparatus of the indirect transfer system described above. The image forming apparatus of this type includes two first intermediate transfer members 34A and 34B that rotate independently from each other. Respective images formed on two photosensitive drums 1Y and 1C of four photosensitive drums 1Y, 1C, 1M, and 1B in the image forming units are transferred onto the first intermediate transfer member 34A at first transfer positions P5 and P6 in superimposition with each other. Respective images formed on the remaining two photosensitive drums 1M and 1B are transferred onto the first intermediate transfer member 34B at first transfer positions P7 and P8 in superimposition with each other. The first intermediate transfer members 34A and 34B are rotationally driven by first intermediate transfer motors 35A and 35B. Single-color toner images are formed on the respective photosensitive drums 1, and, by activating contacting and separating mechanisms 4 so that the transfer rollers 3 contacts the first intermediate transfer members 34, sequentially transferred onto the first intermediate transfer members 34.
The image forming apparatus includes a drum-like second intermediate transfer member 36, onto which respective images transferred onto the two first intermediate transfer members 34A and 34B are superimposed one another and transferred at second transfer positions P9 and P10, and the second intermediate transfer member 36 is driven by a second intermediate transfer motor 37. The image forming apparatus also includes a transfer roller 38 that transfers an image, transferred onto the second intermediate transfer member 36, onto transfer paper P at a third transfer position P11, and a conveyor belt 39 that rotates in a direction of arrow in
The amplitude A and the initial phase α are obtained from the equation shown in
X=B−1Y (1)
The obtained matrix X is rearranged by equation (2) as follows:
Then, the amplitude A and the initial phase α can be obtained with equations (3) and (4), respectively, as follows:
A=√{square root over (S2+C2)} (3)
α=tan−1(C/S) (4)
Thus, the amplitude A and the initial phase α, i.e., fluctuation components corresponding to one rotation cycle of the photosensitive drum 1, can be obtained.
Reference PLL clocks (waveform 6) are generated to offset the calculated fluctuation components and pulse widths thereof can be stored in the memory 54 in the order from the home position. Next, the generated reference PLL clock is output to perform PLL control together with a signal (waveform 5) of the encoder 57 at the motor shaft, thereby rotationally driving the motor 13. Rotational fluctuation of the photosensitive drum 1 is calculated and written in the memory at the time of out-of-color registration measurement or at the time of factory shipment. The measurement at the time of factory shipment is stored in a non-volatile memory.
A waveform diagram in
For example, when phases of the photosensitive drums 1C, 1M, and 1B for respective colors are matched to one another based on the photosensitive drum 1Y for Y color, rotation speeds of the photosensitive drums 1C, 1M, and 1B are adjusted so that phases of the photosensitive drums 1C, 1M, and 1B match the phase of the photosensitive drum 1Y. Thus, the phases of the four photosensitive drums 1Y, 1C, 1M, and 1B match one another. When the four phases match one another, a clock is generated from data stored in the memory unit 72 and the generated clock is output. When the motor controllers 55Y, 55C, 55M, and 55B of the respective photosensitive drums 1Y, 1C, 1M, and 1B output LOCK signals from the PLL circuits 73, image formation becomes possible.
Time that elapses with rotation from an exposure point at which each of the photosensitive drums 1Y, 1C, 1M, and 1B is exposed to a transfer point is calculated by a measurement sensor 66, whose output varies according to adhering toner between the exposure point and the transfer point on optical design, and calculating the time taken from exposure through development to sensor output from the PLL reference clock width stored in the memory unit 72. Because the time elapsing from the position of the measurement sensor 66 to the transfer point is calculated based on design, the time from the exposure point to the transfer point can be determined consequently. However, high precision in an attaching position of the measurement sensor 66 and high sensor precision are required.
Phase matching in the embodiment is performed at the time of correcting out-of-color registration. That is, the out-of-color registration can be reduced by adjusting the rotation speeds of the photosensitive drums 1Y, 1C, 1M, and 1B for respective colors such that the time, from an exposure point at which an image of each color is exposed to a transfer point at which the image is transferred, is the same for respective colors. Regarding rotation target speeds of the photosensitive drums 1Y, 1C, 1M, and 1B, speed ratios are defined by the set target speeds, and clock widths multiplied by the speed ratios are obtained when reference PLL clock width data stored in the memory unit 72 is read to obtain speed set values.
When a second detection pattern 86 is used, predetermined lines extending in a main scanning direction are transferred on belts for respective colors. The lines on the intermediate transfer belt 5 are irradiated with light from the light source 88. The photosensor 89 detects reflected light, and calculates a deviation amount of the line from a target position. Therefore, a light reflection type sensor is used herein.
As a method for detecting the out-of-color registration (position deviation), there is also a method that uses a color charge coupled device (CCD) to detect out-of-color registration (position deviation) of respective colors from red, green, and blue (RGB) output results of the color CCD. In either case, phase matching is performed simultaneously at the time of such out-of-color registration detection or at the time of correction.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
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