Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1998-08-17
2001-02-13
Brase, Sandra (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S115000, C347S232000, C399S038000
Reexamination Certificate
active
06188419
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color image-forming device, such as a color digital copy machine, which, based on color digital image signals, forms color images using a plurality of laser recording sections.
BACKGROUND OF THE INVENTION
In color image-forming devices such as color digital copy machines, generally, an image of a color original, inputted through a scanner, undergoes predetermined image processing to color separate and color convert the image into image data for each color, and a color printer section, which reproduces the image by image data for each color, outputs an image of the color original.
In addition, recently color digital copy machines have appeared on the market which, for high-speed reproduction of high-resolution color originals, include an image-forming device which uses laser recording scanning. In color digital copy machines of this type, by means of a laser deflection scanning section provided in each laser recording section, laser light modulated in accordance with digital image signals is guided to and performs scanning of a photoreceptor. The chief members of this laser deflection scanning unit are a rotating polygon mirror (hereinafter referred to as the “polygon mirror”) and a motor which rotates the polygon mirror at high speed.
Further, recently color digital copy machines have appeared on the market which, in order to improve repeatability of black and of the color image as a whole, are typically provided with a Bk (black) recording section in addition to Y (yellow), M (magenta), and C (cyan) recording sections. For this reason, a monochrome mode is provided in addition to color mode, and thus both color and monochrome copying are possible.
In this kind of color digital copy machine, monochrome copying is set to be performed faster than color copying. This is because, in the case of, for example, the multiple revolution process method, which uses a single photoreceptor, color copying is a four-color process and monochrome copying a one-color process, and thus monochrome copying is necessarily faster. It is also due to the much greater frequency of monochrome over color copying.
In the tandem method, which uses a plurality of photoreceptors, unlike the multiple revolution process method, color and monochrome copying are performed at the same speed, but in order to respond to the demand for faster monochrome than color copying, process speeds such as surface speed of the photoreceptor, transport speed of the recording paper, etc., and the operating speed of the laser recording section which includes the laser scanning unit for black, are set faster than in the color mode.
In this case, the rotation speed of the motor which rotates the polygon mirror of the laser scanning unit of the laser recording section for black is switched between two speeds, one for monochrome mode and one for color mode. Further, if, during waiting, the motor is rotated at a waiting speed slower than that during color mode copying, the motor must be controlled by switching among three speeds.
In contrast, Japanese Unexamined Patent Publication No. 4-247418/1992 (Tokukaihei 4-247418) discloses a structure, in a monochrome laser printer, for reducing scanning density by skipping certain surfaces of the polygon mirror.
However, with the foregoing color digital copy machines structured so as to switch the speed of the motor of the laser recording section, a problem arises due to switching the speed of the motor which rotates the polygon mirror. When switching between monochrome and color modes (especially from monochrome to color), it takes a long time to obtain the first copy.
In other words, in switching the motor speed of the laser recording section for black, when monochrome mode is switched to color mode, it is necessary to bring the motor speed of the laser recording section for black into conformity with the motor speed of the laser recording sections for color, and to synchronize their mirror surfaces, but it takes a long time to attain this synchronization.
This is because it is difficult to stabilize the motor speed of the polygon mirror when its speed is reduced from the high-speed monochrome mode to the low-speed color mode, and this stabilization requires a great amount of time. As a result, the start of copying immediately after switching the copy mode is delayed, and the time required to obtain the first copy is lengthened. Incidentally, with conventional technology, motor speed stabilizes relatively quickly when motor speed is increased.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide, in a color digital copy machine having a monochrome mode and a color mode, a color image-forming device able to improve the efficiency of copying operations by making switching between the two modes smoother.
In order to attain the foregoing object, an image-forming device according to the present invention includes an image-forming section, provided with a recording section for color image formation and a recording section for monochrome image formation, each of which performs optical scanning of a photoreceptor by using a rotating polygon having a reflective mirror on at least one surface thereof to guide to the photoreceptor light modulated in accordance with image information; the image-forming section forming an image based on image information formed on the photoreceptor; and process speed switching means, which switch process speed of the image-forming section such that process speed during forming of monochrome images is faster than during forming of color images; in which the recording section for monochrome image formation is provided with a first scanning mode, which corresponds to a high process speed, and a second scanning mode, which corresponds to a low process speed, and which performs scanning with a scanning density equivalent to that of the recording section for color image formation, without changing rotation speed of the rotating polygon having a reflective mirror on at least one surface thereof. In this structure, during forming of color images (in color mode), the process speed switching means switch to a process speed slower than that during forming of monochrome images (in monochrome mode), and the laser recording section for monochrome image formation uses the second scanning mode, which performs laser scanning with a scanning density equivalent to that of the recording section for color image formation, without changing the rotation speed of the rotating polygon having a reflective mirror on at least one surface thereof. Thus it is possible to switch instantaneously from monochrome to color mode. Further, in monochrome mode, the process speed switching means switch to the faster process speed, and the laser recording section for monochrome image formation uses the first scanning mode corresponding to a high process speed, without changing the rotation speed of the rotating polygon. Thus it is possible to switch instantaneously from color to monochrome mode.
Accordingly, when switching between monochrome and color mode, and in particular when switching from monochrome mode to color mode, the time required to obtain the first copy can be shortened, and the efficiency of copying operations can be improved.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.
REFERENCES:
patent: 4578689 (1986-03-01), Spencer et al.
patent: 4965749 (1990-10-01), Straayer
patent: 5208608 (1993-05-01), Okuyama et al.
patent: 5436647 (1995-07-01), Kasahara
patent: 0 356 238 (1990-02-01), None
patent: 2 267 195 (1993-11-01), None
patent: 4-247418 (1992-09-01), None
Fujimoto Osamu
Katamoto Koji
Oda Ayumu
Shimazawa Yoichi
Yoshiura Syoichiro
Brase Sandra
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Sharp Kabushiki Kaisha
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