Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-12-06
2002-01-29
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S216100, C347S235000, C250S234000
Reexamination Certificate
active
06342963
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an optical scanning apparatus. More specifically, the present invention is directed to such an optical scanning apparatus capable of correcting positional shifts contained in plural images to be synthesized, which is used in an image forming apparatus in which a plurality of optical beams are separately scanned over a photosensitive member, and a plurality of images formed on this photosensitive member are synthesized with each other to output a single synthesized image.
2. Description of the Related Art
Conventionally, images forming apparatuses are used in printers and copying machines. In these image forming apparatuses, optical beams which are modulated in response to images to be formed are scanned over photosensitive members so as to form electrostatic latent images on these photosensitive members, so that desirable images are formed on the photosensitive members. Very recently, since these electronic appliances are manufactured in digital modes and also color modes, the image forming apparatuses with employment of the above-explained structures are widely employed in these digital/color electronic appliances. A color image may be formed in such a manner that, for example, images having different four colors (e.g., C, M, Y, K) are sequentially formed on a photosensitive member, while these four color images are overlapped with each other on a single photosensitive member. However, this color image forming operation would own such a problem that a lengthy time is required until the desirable image is finally formed.
To avoid this problem, a so-called “tandem” type image forming apparatus has been proposed. In this tandem type image forming apparatus, a plurality of photosensitive members are provided, the respective photosensitive members are scanned/exposed at the same time by a plurality of optical beams to form images having different colors from each other on the respective photosensitive members, and then these images having the different colors are overlapped with each other on the same transfer member. As a result, a desirable color image can be formed. Since this tandem type image forming apparatus simultaneously forms the images having the respective colors at the same time, the time required to form the color image can be largely shortened.
However, in this tandem type image forming apparatus, when the images having the different colors are overlapped with each other, these are certain possibilities that the positional shifts are easily produced due to the fluctuations in the optical characteristic of the optical beams corresponding to the respective color images. Also, these positional shifts of these images may be apparently and visually recognized in the color image. Accordingly, the color shifts must be corrected in order to obtain a high grade image. While the image forming apparatus is manufactured, even when the respective components of this image forming apparatus are adjusted so as to cancel the color shifts, if the peripheral environments such as temperatures are varied, then the color shifts are produced due to some reason, for instance, the arranging positions of the optical components.
Japanese Patent No. 2748971 describes the following color shift corrections employed in the tandem type image forming apparatus. That is, the sensor for sensing the positional shifts of the beams are provided in the vicinity of the respective photosensitive drums. The sensor sense the beam positions along the sub-scanning direction so as to control the write timing along the sub-scanning direction, so that the color shifts along the sub-scanning direction can be corrected.
As another color shift correcting method, the following correcting method is known. That is, while the patterns (for example, mark “+”) capable of easily being sensed the color shifts are formed on the photosensitive members, these patterns are read out by the image reading apparatus to be sensed the color shifts. Then, the color shifts are corrected by changing the positions of the beams entered into the photosensitive drums by moving the reflection mirrors, or by controlling the write timing along the sub-scanning direction.
However, the conventional color shift correcting method described in Japanese Patent No. 2748971 owns the following drawback. That is, since the sensor for sensing the positional shift amounts along the sub-scanning direction are provided in correspondence with the photosensitive drums, a positional relationship between a newly replaced photosensitive drum and the relevant positional shift-amount sensor must be adjusted when the old photosensitive drum is replaced by this new photosensitive drum. As a result, the replacing work of the photosensitive drum unit becomes cumbersome. Also, since the positional shift-amount sensor are arranged in the vicinity of the photosensitive drums, there is another problem that these positional shift-amount sensors are contaminated by dust and the like.
Also, in the case that the color shifts are sensed based upon the color shift sensing patterns, since the color shift sensing patterns must be formed on the photosensitive drums, the complex control operation is required. Also, the image reading apparatus for reading the color shift sensing patterns is expensive. The image forming apparatus is made in high cost, and furthermore, the overall dimension of this image forming apparatus is increased so as to secure the space for arranging this image reading apparatus.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-explained problems. This invention provides such an optical scanning apparatus capable of correcting a positional shift contained in a plurality of images with employment of a simple and low-cost arrangement, while these plural images are synthesized with each other to thereby output a synthesized image as a single image.
To achieve the above-explained advantages, an optical scanning apparatus, according to the present invention, is featured by that an optical scanning apparatus used in an image forming apparatus for scanning a plurality of optical beams on photosensitive members and for synthesizing a plurality of images formed on the photosensitive members to output a synthesized image as a single image, the optical scanning apparatus comprising: a light source for projecting the plurality of optical beams; deflector for deflecting the optical beams; first beam sensor for sensing positions of the respective optical beams along an optical beam scanning direction; second beam sensor for sensing positions of the respective optical beams along a direction intersected with the scanning direction; and modulation controller for controlling a modulation of each of the plural optical beams projected from the light source based upon the sense results obtained from the first beam sensor and the second beam sensor in such a manner that a positional shift occurred when a plurality of images formed by the respective optical beams are synthesized with each other is suppressed.
In an image forming apparatus in which the optical scanning apparatus according to the present invention, while a plurality of optical beams may be scanned over the photosensitive members to form a plurality of images, these plural images are synthesized with each other to output the synthesized image as a single image. As a consequence, for example, when these plural images are such image having different colors from each other, these plural images may be synthesized with each other and then the synthesized image becomes a multi-color image (when colors of plural images are K, Y, M, C, a full color image is outputted). It should be noted that a total number of photosensitive members might be basically selected from 1, or plural number. However, when an image forming apparatus is arranged in such a way that a plurality of photosensitive members are provided and images are formed on the respective photosensitive members at the same time by way of
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
Schuberg Darren
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