Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-05-12
2001-06-19
Beatty, Robert (Department: 2852)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S118000
Reexamination Certificate
active
06249305
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus.
Heretofore, there has been a color image forming apparatus wherein a laser beam scanning unit is housed, and an image carrier is caused to make several turns to form thereon toner images respectively for Y, M, C and K and these toner images are superposed to form a color image. This color image forming apparatus has been inexpensive because it contains only one laser beam scanning unit, but it has been time-consuming for forming a color image because it has been necessary for the image carrier to make several turns. Under this situation, there is available an image forming apparatus which houses therein plural laser beam scanning units for shortening a period of time for forming a color image. In this image forming apparatus, a color image can be formed in a short period of time because toner images respectively for Y, M, C and K are formed simultaneously in the same time zone through scanning of plural laser beams conducted by plural laser beam scanning units, and these toner images are superposed on an image carrier or on a recording medium.
In an image forming apparatus having therein plural laser beam scanning optical units, when a position of a latent image formed by the laser beam scanning optical unit is relatively deviated, image quality troubles such as shear in colors and shade variation are caused. Though there is considered a device wherein the position deviation mentioned above is automatically adjusted through bending, tilting and parallel movement conducted by a position changing unit utilizing a mirror, a lens and a motor in the laser beam scanning optical unit or by a position changing unit utilizing a dimensional change caused by thermal expansion, there are caused problems that an apparatus has to be made larger or the cost therefor has to be high. Further, there are several types for the position deviation, and even the direction thereof is roughly divided into two types including the primary scanning direction and the sub-scanning direction, and each of them is further subdivided into total magnification and partial magnification. Among these, the magnification in the primary scanning direction is relatively easy to control because it can be controlled electrically as is corrected by changing a dot clock. However, for the curved scanning line and relative deviation of parallelism, it has been necessary to make the complicated control mentioned above.
The first object of the invention, therefore, is to provide a scanning optical unit and an image forming apparatus wherein plural color images formed by plural laser beams emitted from plural laser scanning optical units are not deviated in the sub-scanning direction when they are superposed on an image carrier or on a recording medium, and thereby an appropriate color image with high quality can be obtained.
In the internal arrangement of a color image forming apparatus, it is common that a drum-shaped photoreceptor representing an image carrier is arranged at the central portion, an exposure system and a developing unit both representing an image forming means are arranged to surround the photoreceptor, a transfer means is arranged to be directly under the photoreceptor, and a sheet-feeding cassette is arranged at the lowermost portion in the color image forming apparatus.
Further, it has been attempted to increase a degree of freedom for layout inside a color image forming apparatus by using a belt-shaped photoreceptor (hereinafter referred to also as a belt-shaped image carrier) wherein a photoreceptor layer is provided on a belt-shaped base body trained about driving rollers, in place of the drum-shaped photoreceptor.
For example, there has been known a color image forming apparatus wherein each of plural developing units is provided with different color toner, and a latent image for each color is formed on a belt-shaped image carrier by each of plural exposure systems, and toner images each being for each color are developed to be superposed on the belt-shaped image carrier while it makes one turn, thus the toner images are collectively transferred onto a transfer sheet taken out of a sheet-feeding cassette arranged under the belt-shaped image carrier for obtaining a color image. The image forming system employed in the image forming apparatus mentioned above is called a single-rotation superposing system.
For example, TOKKAIHEI 3-80286 discloses a color image forming apparatus of a single-rotation superposing system, wherein a belt-shaped image carrier is arranged to be long sideways, and plural developing units and plural exposure systems representing image forming means are arranged under the belt-shaped image carrier. In the exposure system in this example, light emitted from a light-emitting diode is converged by a SELFOC lens so that an image is formed on the belt-shaped image carrier.
TOKKAIHEI 4-102874 discloses a color image forming apparatus of a single-rotation superposing system, wherein a belt-shaped image carrier is arranged to be long sideways, plural developing units are arranged under the belt-shaped image carrier, and plural exposure systems representing image forming means are arranged under the developing units. In this example, the exposure system is a scanning exposure system which deflects a laser beam by the use of a rotary polygon mirror.
TOKKAIHEI 5-158319 discloses a color image forming apparatus of a single-rotation superposing system, wherein a belt-shaped image carrier is arranged to be long lengthwise, and plural developing units and plural exposure systems are arranged on both sides of the belt-shaped image carrier. The exposure system in this example is a scanning exposure system.
In the color image forming apparatus described in TOKKAIHEI 4-102874, scanning exposure systems are arranged under the belt-shaped image carrier which is long sideways, and a mirror is arranged to change temporarily a path for the laser beam reflected on the polygon mirror. The mirror is sometimes deformed depending on temperature and humidity to cause distortion. When the mirror is distorted, an electrostatic latent image formed on the belt-shaped image carrier is distorted, and quality of outputted images is sometimes deteriorated, which is a problem. Further, since the scanning exposure systems are arranged under the developing units in this color image forming apparatus, toner sticks to the scanning exposure systems including the mirror, making the accurate exposure to be impossible, and quality of outputted images is deteriorated, which is a problem.
When an exposure system is arranged under a belt-shaped image carrier as in the color image forming apparatus described in TOKKAIHEI 3-80286, it results in the arrangement wherein toner falls and lies on the SELFOC lens due to the exposure direction. If toner falls and lies to interfere with an optical path of a laser beam, there is caused a problem that accurate exposure can be performed and quality of an outputted image is deteriorated. In addition, when comparing an exposure system employing a light-emitting diode array with a scanning exposure system, the exposure system employing a light-emitting diode array has a problem that it is not suitable for high quality outputting, because of the reason that a shape, a size and a position of a light spot forming an image on the surface of an exposure system photoreceptor can not be controlled accurately to the extent of the scanning exposure system.
When a belt-shaped image carrier is arranged to be long sideways as those in the color image forming apparatus described in TOKKAIHEI 4-102874 and that described in TOKKAIHEI 3-80286, there is caused a problem that a large floor space is needed for installation of the color image forming apparatus.
In the color image forming apparatus described in TOKKAIHEI 5-158319, a belt-shaped image carrier is arranged to be long lengthwise, and thereby a space occupied sideways by the belt-shaped image carrier is reduced. However, a floor space needed for substantial ins
Ikeda Masaaki
Miyamoto Takayuki
Okugawa Yuji
Shigetomi Masahiro
Tajima Naoki
Beatty Robert
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Konica Corporation
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