Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1998-07-14
2001-03-20
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S248000
Reexamination Certificate
active
06204865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for forming a color image for one frame by superposing a plurality of frame images.
2. Related Background Art
Conventionally, a color image forming apparatus for printing out color image data, e.g., a laser beam printer (LBP), forms a latent image in units of lines on a photosensitive body by a main scanning means (e.g., by irradiating a laser beam onto the photosensitive body by a rotary polygon), forms images in units of color components using developing agents of individual color components such as magenta (M), cyan (C), yellow (Y), black (BK), and the like, and transfers and superposes the images in units of color components onto a paper sheet fixed on a transfer drum, thus forming a color image.
Another image forming apparatus temporarily superposes images in units of color components formed on the photosensitive body onto an intermediate transfer body, and simultaneously transfers a color image on the intermediate transfer body onto a paper sheet.
In such conventional image forming apparatuses, the photosensitive body and transfer drum or intermediate transfer body are driven at given velocities in a direction (sub-scanning direction) perpendicular to the main scanning direction, and every time the transfer drum or intermediate transfer body completes one rotation, each color image is superposed on the paper sheet on the transfer drum or the intermediate transfer body. Also, in still another image forming apparatus, images in units of recording color components are formed on the photosensitive body to overlap each other, and the formed color image is simultaneously transferred onto a recording paper sheet.
In the conventional color image forming apparatus, the image quality of a color image often deteriorates due to offsets of the superposing positions of individual color images. In order to prevent the superposing positions of the individual color images from offsetting, a method of controlling the position upon superposing each color image is important.
For this purpose, for example, the following technique has been proposed. That is, a main scanning start signal (BD signal) is frequency-divided to obtain an integer number of BD signals during one rotation of the photosensitive body or intermediate transfer body, and these BD signals are used as reference clocks for a motor for driving the photosensitive body or intermediate transfer body. In this way, the laser scanning line is always scanned at an identical position independently of the number of rotations of the photosensitive body or intermediate transfer body, thus allowing easy color registration.
However, a BD signal is generated by scanning a laser beam onto the photosensitive body by a rotary polygon, and detecting it by a BD sensor located in the vicinity of the main scanning start position of one line of the photosensitive body or the corresponding position in the optical path. Hence, with the above-mentioned technique, since the photosensitive body or intermediate transfer body cannot be driven before the BD signal is detected, a time loss is produced from when a laser is turned on to detect a BD signal after the beginning of image formation until the BD signal is detected, thus prolonging the image formation time.
The laser beam, for BD signal detection, repetitively scans an identical position on the photosensitive body before the photosensitive body begins to rotate, Thus, photosensitive body unwantedly develops a so-called drum memory, and cannot be uniformly charged even via the charge removal and charging processes of the photosensitive body later, resulting in a short service life of the photosensitive body.
Furthermore, the laser must always be ON to detect the BD signal so as to drive the photosensitive body or intermediate transfer body, thus shortening the service life of the laser.
SUMMARY OF THE INVENTION
The present invention has been made to solve the conventional problems, and has as its principal object to provide an apparatus which can form a high-quality image by reliably adjusting the superposing positions of frame images to each other when a single image is formed by superposing a plurality of frame images. In order to achieve this object, according to the present invention, a rotary polygonal mirror and image carrier are controlled to operate in association with each other to reliably adjust the superposing positions of frame images, thus forming a high-quality image.
Especially, it is an object of the present invention to provide a specific technique for controlling the rotary polygonal mirror and image carrier in association with each other.
In order to achieve the above objects, according to one preferred embodiment of the present invention, there is provided an image forming apparatus comprising:
a rotary polygon for forming a latent image on an image carrier by scanning the image carrier, which moves in a sub-scanning direction, in a main scanning direction using a light beam modulated based on image data;
first generation means for generating a first timing signal by detecting the light beam that has scanned a predetermined position;
second generation means for generating a second timing signal independently of the detection; and
driving means for moving the image carrier in the sub-scanning direction by selectively using the first and second timing signals.
According to another preferred embodiment of the present invention, there is provided an image forming apparatus comprising:
a rotary polygon for forming a latent image on an image carrier by scanning the image carrier, which moves in a sub-scanning direction, in a main scanning direction using a light beam modulated based on image data;
first generation means for generating a detection signal which indicates that the light beam that has scanned a predetermined position; and
driving means for rotating the image carrier once in the sub-scanning direction by rotating N times (N: a natural number) on the basis of a reference signal obtained by frequency-dividing the detection signal, the image carrier completing one rotation while M detection signals (M: a natural number) are generated,
wherein the driving means generates X signals (X: a natural number) indicating the rotation timing while the driving means completes one rotation, and
a frequency division ratio is given by n=N×X/M.
Other objects and features of the present invention will become apparent from the following detailed description of the embodiments taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4704698 (1987-11-01), Reiniger
patent: 5083140 (1992-01-01), Peterson et al.
patent: 5233402 (1993-08-01), Yagi et al.
patent: 5291222 (1994-03-01), Ohashi
patent: 5570195 (1996-10-01), Hondo
Honbo Tsunao
Noguchi Junichi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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