Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-06-03
2001-05-08
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S248000
Reexamination Certificate
active
06229559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for forming a latent image on a photo receptor belt.
2. Description of the Related Art
There have been developed devices for forming a color image using a photo receptor belt on which a latent image will be formed for each color. In such a color image forming device, there is a possibility of the photo receptor belt moving like a snake, resulting in displacements of the photo receptor belt in the primary scanning direction. Since such movements of the photo receptor belt cause displacements of a latent image for each color, it is very important to precisely keep the writing start positions for colors at the same position in the primary scanning direction on the photo receptor belt. To prevent color deviation, several image forming apparatuses have been proposed as described hereafter.
A conventional image forming apparatus is disclosed in Japanese Patent Unexamined Publication No. 4-181276. A photo-sensor is used to detect displacements of the photo receptor belt in the primary scanning direction. The photo-sensor is composed of a number of sensor elements arranged in a line and is placed in the inner side at an edge portion of the photo receptor belt such that the end portion of the photo-sensor protrudes from the edge line of the photo receptor belt. Therefore, the photo-sensor can detect the laser beam traversing only a range from the end thereof to the edge of the photo-receptor belt. The distance from the end thereof to the edge of the photo receptor belt is measured by counting the number of sensor elements therebetween. On a first turn of the photo receptor belt, a measured count value is stored. When the photo receptor belt is turned for a second time, a count difference between the first measured count value and the second measured count value is calculated. The count difference is used to determine the write start position on the photo receptor belt.
Another conventional image forming apparatus is disclosed in Japanese Patent Unexamined Publication No. 5-119574. A plurality of primary scanning laser units are provided to form latent images on the photo receptor belt, respectively. A photo-sensor for each primary scanning laser unit is placed to detect a pre-pattern formed on the edge portion of the photo receptor belt when the photo receptor belt is scanned with a laser beam by the primary scanning laser unit. The position detection signal of the photo-sensor is used to determine the write start timing.
However, in the case of the conventional apparatus using the count difference, a memory for storing the count difference is needed and further a controller is burdened with the distance measurement and displacement calculation.
On the other hand, in the case of the conventional apparatus using pre-pattern position detection signals, it is necessary to provide the photo receptor belt with the pre-patterns. Further, since the write start timing is determined using only the pre-pattern detection signal, the write start timing cannot be determined with sufficient precision.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an image forming apparatus and method, which can form an image on a photo receptor belt at a precise position with simplified circuit configuration.
It is another object of the present invention to provide an image forming apparatus and method, which prevent color deviation of an image formed on a photo receptor belt with reduced burden upon a controller.
According to the present invention, a latent image is formed on a photo receptor belt by scanning the photo receptor belt with a laser beam modulated in accordance with the image data. A clock signal controls the modulation process. After detecting an edge of the photo receptor belt to produce an edge detection signal, the clock signal is synchronized to the edge detection signal to produce a sync clock signal. The start time of modulating the laser beam according to the image data is determined based on the sync clock signal.
According to another aspect of the present invention, a first clock generator generates a clock signal and an edge detector detects an edge of the photo receptor belt to produce an edge detection signal. A second clock generator generates a sync clock signal by synchronizing the first clock signal to the edge detection signal. An image signal generator generates the image data beginning at a start time determined based on the sync clock signal.
Since the start time of the sync clock signal with respect to the edge of the photo receptor belt is kept constant, the write start position of the image data is at a constant distance from the edge of the photo receptor belt independently of displacements of the photo receptor belt.
Therefore, in the case of color image forming, color deviation of the image formed on the photo receptor belt can be eliminated, resulting in high-quality color image.
Further, since the sync clock signal is synchronized to the edge of the photo receptor belt, it is not necessary to use the reference signals of the laser units to determine the write start positions, respectively. The respective reference signals of the laser units would vary, resulting in variations in the write start positions. Therefore, by using the sync clock signal synchronized to the edge of the photo receptor belt, the precise write start position of the image data can be achieved.
REFERENCES:
patent: 5737003 (1998-04-01), Moe et al.
patent: 5760816 (1998-06-01), Morrison
patent: 5978003 (1999-11-01), Brenner, Jr.
patent: 4-9975 (1992-01-01), None
patent: 4-181276 (1992-06-01), None
patent: 5-119574 (1993-05-01), None
Le N.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Pham Hai C.
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