Recorders – Writers – Receiver and marker movable
Reexamination Certificate
2000-11-28
2002-06-11
Pendegrass, Joan (Department: 2852)
Recorders
Writers
Receiver and marker movable
C347S234000
Reexamination Certificate
active
06404448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color-image forming apparatus, and relates, more particularly, to a color-image forming apparatus of an electronic photographing system such as a laser printer and a laser-copying machine.
2. Description of the Related Art
Along with the progress of digitalization and coloring of images in recent years, there has been an increasing trend to utilize a color-image forming apparatus, like a laser printer and a laser-copying machine, which expose a photosensitive member by scanning it with laser beams. Particularly, in the case of forming a color image, the four colors black, yellow, magenta and cyan are superimposed. Therefore, this type of color-image forming apparatus has lower productivity than that of the conventional black and white image forming apparatus. In order to solve this problem, a tandem color-image forming apparatus that simultaneously forms four color images has been devised.
The tandem color-image forming apparatus has a plurality of photosensitive members. This color-image forming apparatus exposes each photosensitive member with each laser beam that has been modulated according to image data which has divided image into each of the color component. The color-image forming apparatus then develops these photosensitive members, and superimposes the developed color images on the same transfer medium, to thereby form a color-combined colored image. Therefore, the tandem color-image forming apparatus has a substantially improved productivity.
However, on the other hand, unless image positions of the colors are matched correctly, there occurs a shift in the position of the colors due to variations in the optical characteristics of the laser beams emitted from an exposure apparatus. Thus, it becomes impossible to maintain the quality of a printed image. There are five items that are necessary for the positioning. They are a write start position of a scanning line in a main scanning direction (hereinafter to be referred to as side registration), a write start position of a scanning line in a sub-scanning direction (hereinafter to be referred to as lead registration), a write ending position of the scanning line in the main-scanning direction, or a print width (hereinafter to be referred to as a scale factor), a curve of the scanning line itself (hereinafter to be referred to as a scanning line curve), and an inclination of the scanning line (hereinafter to be referred to as a scanning line inclination). A high-quality image can be formed only when conditions relating to these five items are satisfied.
Further, according to the tandem color-image forming apparatus, the type of the exposure apparatus is broadly classified into two types.
FIG. 16
shows an apparatus having four scan exposure devices
300
arranged therein, each device having one laser beam (hereinafter to be referred to as a four-series tandem system). The four-tandem system has four scan rotation motors
302
for the four exposure devices respectively. Therefore, a feature of this system is that independent laser beam scanning positions exist.
An apparatus for scanning four light beams with one motor is disposed in Japanese Patent Application Laid-Open Publication (JP-A) No. 3-142412 (This system will hereinafter be referred to as a spray paint system). As the spray paint system has one scan rotation motor as a deflector, this system is characterized by the laser beam positions being related to each other.
First, the four-series tandem color-image forming apparatus will be described in detail. As shown in
FIG. 16
, the color-image forming apparatus of the four-series tandem system has four separate scan exposure devices
301
. These scan exposure devices
300
expose color images of K (black), Y (yellow), M (magenta), and C (cyan) respectively. Each scan exposure device
300
carries out an image exposure for each color on a photosensitive member
304
provided for each color, to thereby form an electrostatic latent image. After completing the exposure, each electrostatic latent image on each photosensitive member
304
is developed by each developer
306
. Each developed image is transferred onto a transfer belt
308
as a single transfer member. At the time of this image transfer, the respective colors are sequentially superimposed to form a color image. This system combines the colors (that is, the positioning of scan beams) by taking the above-mentioned five items into consideration. According to this color-image forming apparatus of the four-series tandem system, it is necessary to provide a special mechanism for controlling the phases of the rotation of the four motors, as these motors operate independently of each other.
On the other hand, according to the color-image forming apparatus of the spray paint system, generally, the scan exposure device itself is relatively compact, as the laser beams corresponding to the respective colors are scanned by one motor. A color image is formed in a similar manner to that of the above-described color-image forming apparatus of the four-series tandem system. However, a feature of the spray paint system is that it is not necessary to provide a special control mechanism for the motor, as the scan laser beams of the respective colors are linked with each other and scanned. A difference between these characteristics can be considered as the degree of freedom in positioning in the sub-scanning direction.
In the case of the four-series tandem system, there is a large amount of freedom in the timing of the positioning, as the motors are independent of each other. In other words, it becomes possible to position the colors at substantially the same position. It is possible to achieve this by controlling the rotation phases of the motors. On the other hand, in the case of the spray paint system, the positioning is carried out in the scan line unit, as the laser beams are based on one motor and thus related to each other. It is also possible to control the rotation phases in a unit smaller than the scan line unit based on other techniques. It has been known that according to a high-resolution image forming apparatus developed in recent years, a color deviation is not so noticeable even when the positioning is carried out in a scan line unit. In control based on a scan line unit using two laser beams, a maximum amount of deviation is one half line.
The color matching in the above-described color-image forming apparatuses will be described next. According to the tandem color-image forming apparatus, it is necessary to carry out the positioning by correcting the side registration, the lead registration, the scale factor, the scan line curve, and the scan line inclination. Among these items to be corrected, the correction of the lead registration that is a feature of the present invention will be described. Prior-art techniques will be described, with a detecting system and a control system being described in that order.
According to an apparatus described in JP-A No. 2-105169 as a first prior-art technique, for detecting a color deviation, at first, each photosensitive member is exposed and an image is developed using pattern images for measuring each color at a predetermined timing. Each pattern image of each color formed by this operation is transferred onto a transfer belt. Information on a position of color deviation is obtained by detecting position information of each pattern image with a reading sensor. According to this invention, a reflection-type phototransistor is used as a reading sensor. Therefore, in actual practice, a gap between pattern images of each color is obtained as color deviation information. It is possible to determine a deviation in the position of each color by measuring an output corresponding to the interval of the gap between the colors. Based on a result of the color deviation obtained in this way, the lead registration which is the write start position in the sub-scanning direction is corrected. There is also a similar method using a CCD sensor as a re
Fuji 'Xerox Co., Ltd.
Morgan & Lewis & Bockius, LLP
Pendegrass Joan
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