Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-03-16
2001-03-20
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S235000, C358S501000
Reexamination Certificate
active
06204866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image forming apparatus such as a digital color copier, printer or the like, and, in particular, to a color-image forming apparatus in which color displacement does not occur, and, thereby, it is possible to form high-quality color images.
2. Description of the Related Art
Recently, in order to improve the image-formation efficiency, as disclosed in Japanese Laid-Open Patent Application No.
4-175774
, in an image forming apparatus for forming multi-color images from image information obtained through an image reading device or sent from a host apparatus, two color images, each having a standard size, such as A-4 size, are formed on a photosensitive belt having a length more than twice that of the standard size, and two toner images formed on the photosensitive belt are transferred to transfer paper sheets which are fed successively. Alternatively, as disclosed in Japanese Laid-Open Patent Application No.
5-227386
, a color image is formed on a first transfer paper sheet held by a transfer drum, which can hold a plurality of transfer paper sheets at a time, based on image data transmitted from an image reading device, and, then, color images are formed on second and following transfer paper sheets based on image data stored in an image memory.
However, when a color image is formed in a manner in which an image, the color of which is a first color (for example, black), is formed using image data transmitted from an image reading apparatus, and, then, images, colors of which are second, third and fourth colors (for example, cyan, magenta and yellow), are formed using image data stored in and read out from an image memory, so that these images are overlaid with each other, timing of a reference signal for positioning an image may be different between the first-color image and the second, third and fourth-color images. Thereby, color displacement may occur.
SUMMARY OF THE INVENTION
The present invention has been devised to solve such a problem, and, an object of the present invention is to provide a color-image forming apparatus in which images, colors of which are respective colors, are overlaid on each other with high accuracy so that color displacement is prevented, and, thereby, it is possible to form high-quality color images.
An image forming apparatus according to the present invention comprises:
a photosensitive drum turning at a uniform angular velocity;
means for writing an electrostatic latent image on the photosensitive drum using a laser beam having an intensity in accordance with image data output by an original reading unit which reads an original and outputs the image data thus obtained from the original;
means for developing the electrostatic latent image formed on the photosensitive drum into a toner image; and
an intermediate transfer belt running at a uniform speed, onto which the toner image is transferred from the photosensitive drum, a reference mark being provided on the intermediate transfer belt;
a memory for storing the image data output by the original reading unit;
means for detecting the reference mark;
means for counting pulses of a motor driving signal and outputting a count value, the pulses being used for driving a scanner motor provided in the original reading unit at different speeds so as to enable the original to be read in different speeds; and
means for determining, based on the count value, a time period between a time the detecting means detects the reference mark and a time the writing means starts writing the electrostatic latent image on the photosensitive drum, when the electrostatic latent image is formed using the image data output by the original reading unit directly and the electrostatic latent image is formed using the image data stored and read out from the memory.
An image forming apparatus according to another aspect of the present invention comprises:
a photosensitive drum turning at a uniform angular velocity;
means for writing an electrostatic latent image on the photosensitive drum using a laser beam having an intensity in accordance with image data output by an original reading unit which reads an original and outputs the image data thus obtained from the original;
means for developing the electrostatic latent image formed on the photosensitive drum into a toner image; and
an intermediate transfer belt running at a uniform velocity, onto which the toner image is transferred from the photosensitive drum, a reference mark being provided on the intermediate transfer belt;
a memory for storing the image data output by the original reading unit;
means for detecting the reference mark;
means for selecting, depending on an arbitrarily set magnification, either pulses of a line synchronization signal or pulses of a motor driving signal, each of the pulses of the line synchronization signal being generated when the laser beam scans the photosensitive drum in a main scan direction and the pulses of the motor driving signal being used for driving a scanner motor provided in the original reading unit at different speeds so as to enable the original to be read at different speeds so as to enable the magnification to be set to different values;
means for counting the pulses of the signal selected by the selecting means and outputting a count value; and
means for determining, based on the count value, a time period between a time the detecting means detects the reference mark and a time the writing means starts writing the electrostatic latent image on the photosensitive drum, when the electrostatic latent image is formed using the image data output by the original reading unit directly and the electrostatic latent image is formed using the image data stored and read out from the memory.
When a color image is formed, the electrostatic latent image is formed using the image data output by the original reading unit directly for a first color, and the electrostatic latent image is formed using the image data stored and read out from the image memory for each of second and following colors.
The selecting means may select pulses of one of the line synchronization signal and the motor driving signal, which one is a signal, the distance moved by a carriage of the original reading unit per pulse of the signal being smaller than the distance moved by the carriage of the original reading unit per pulse of the other signal, the carriage being driven by the scanner motor and used for reading the original by moving in a sub-scan direction.
Thereby, as a result of positioning a range in which an electrostatic latent image formed on the photosensitive drum using pulses of one selected between the line synchronization signal (Lsync) and motor driving signal, the thus-selected signal being such that the moving amount of the carriage per pulse of the signal is smaller than the moving amount of the carriage per pulse of the other signal, it is possible to make the range on the intermediate transfer belt in which the toner image is transferred from the photosensitive drum to be the same when the image data obtained from reading the original through the original reading unit is directly used for image formation and image data read out from the memory is used for image formation, with higher accuracy. As a result, it is possible to prevent shift of position and color displacement, and, thereby, to form images on transfer paper sheets at the same position and to form high-quality color images on transfer paper sheets.
REFERENCES:
patent: 5631691 (1997-05-01), Furuta et al.
patent: 5646749 (1997-07-01), Omi et al.
patent: 4-175774 (1992-06-01), None
patent: 5-227386 (1993-09-01), None
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pendegrass Joan
Ricoh & Company, Ltd.
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