Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2001-10-02
2004-08-03
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S234000, C347S249000
Reexamination Certificate
active
06771296
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an optical scanning device and an image-forming device, and particularly relates to a multicolor image-forming device applicable to color laser printers, color digital copiers and color facsimile devices.
2. Description of the Related Art
One of the optical scanning devices applicable to multicolor image-forming devices is a so-called multi-beam scanning device which includes a plurality of light sources, a drive circuit for driving the light sources individually in a modulating manner, a deflector for deflecting rays emitted from the light sources and a scan-imaging optical system directing the deflected rays towards different surfaces. Surfaces to be scanned are hereinafter referred to as scan surfaces. The multi-beam scanning device is capable of optically scanning the plurality of scan surfaces individually. Therefore, the multi-beam scanning device may serve as an optical scanning device applicable to a multicolor image-forming device. Also, in contrast to a single-beam scanning device, images can be formed without having to rotate a photo-sensitive drum through a plurality of revolution. Thus, multicolor images can be formed at an increased speed and with improved productivity.
One of the image-forming devices of the prior art utilizing a multi-beam scanning device is known from Japanese Laid-Open Patent Application No. 10-148775. A galvano-mirror is used as an optical deflector. Two rays are deflected on one side of the galvano-mirror and two rays are deflected on other side of the galvano-mirror, such that the deflected rays scan corresponding image carrier surfaces respectively in order to record images.
The images recorded on the image carrier surfaces are transferred and superimposed on a single transfer belt or on a single sheet of transfer paper. Thus, the image recorded on one of the image carrier surfaces and the image recorded on another one of the image carrier surfaces need to be formed with high positioning accuracy. Also, each image must have high image magnification accuracy. If the positioning accuracy and the magnification accuracy of each image are not sufficiently high, the resulting image obtained by transferring and superimposing the images will not become sharp and a color offset occurs. Accordingly, the prior art technology cited above includes the steps of arranging two light-receiving elements along a main scan direction, determining a modulation start timing of the light sources based on detection signals of the deflected lights supplied by the two light-receiving elements and correcting the image magnification based on a difference of the timings between the deflected lights detected by the two light-receiving elements.
Another example of the color image-forming device utilizing a multi-beam scanning device is known from Japanese Laid-Open Patent Application No. 11-326804. There are four sets of image-forming devices corresponding to colors required for forming a color image, e.g., four colors such as cyan, magenta, yellow and black. Each set includes a light source, an optical deflector, a scan-imaging optical system and an image carrier. A displaceable diffraction is provided for each set of image-forming device. The magnification factor in the main scan direction of the image to be formed is corrected by displacing each diffracting optical element in a longitudinal direction.
However, with a multi-beam type multi-color image-forming device, there is a need for reducing an offset between images formed on different scan surfaces corresponding to each of the colors in order to reduce the resulting color offset produced when the images are superimposed. Recently, there is a need for a multi-color image-forming device with higher accuracy.
With the prior art multi-color image-forming device, it is particularly difficult to correct the color offset in the main scan direction and thus the accuracy of correction was not sufficient. Therefore, there is a need for a multi-color image-forming device with improved accuracy of correction.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the invention to provide an optical scanning device and an image-forming device which can satisfy the needs described above.
It is another and more specific object of the present invention to provide an optical scanning device which can correct relative dot position offset in the main scan direction for each scan surface.
According to the present invention, an optical scanning device includes:
a plurality of light sources;
a drive circuit connected to the light sources to drive the light sources independently with from each other in a modulating manner;
a deflector having a plurality of deflecting surfaces to deflect rays emitted from the light sources;
scan imaging optical systems directing the deflected rays onto different scan surfaces, respectively;
synchronization detection means for receiving the rays before start writing onto the scan surface and outputting synchronization detection signals;
delay time adjusting means for adjusting delay time, the delay time being a time period after outputting the synchronization detecting signal until starting the writing operation; and
frequency adjustment means for adjusting driving frequencies of the light sources.
With the optical scanning device described above, since the position offsets of dots formed on one scan surface and dots formed on the other scan surface are adjusted to be in an opposite sense at both ends of an effective write-in width, relative position offsets in the main scan direction of the dots formed on different scan surfaces can be corrected.
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Hayashi Yoshinori
Ueda Takeshi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pendegrass Joan
Ricoh & Company, Ltd.
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