Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-11-04
2001-07-03
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S116000, C347S248000
Reexamination Certificate
active
06256054
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color image formation apparatus which exposes a photo receptor belt to light from a plurality of exposure light sources to form a color image of a plurality of colors superposed with each other, and more particularly to a photo receptor belt edge detection apparatus for use with a color image formation apparatus of the type mentioned which detects the position of an edge of the photo receptor belt and eliminates a displacement of a light exposure scanning start position on the semiconductor belt to correct the light exposure scanning start position.
2. Description of the Related Art
Conventionally, an image formation apparatus which employs an electrophotographic system is used in printers, copying machines, facsimile apparatus and other like apparatus. A photo receptor member principally with which an image formation process is performed is formed either as a drum type photo receptor member or as a belt type photosensitive member. A color image formation apparatus which prints in multiple colors frequently uses a photosensitive member in the form of a belt, that is, a photo receptor belt in order to facilitate superposition of a plurality of images of different colors on the photosensitive member.
In a color image formation apparatus which employs a photo receptor belt, it is important to adjust the timing of the writing operation so the start positions on the photo receptor belt in the scanning direction is the same for each color image. Otherwise, there will be misalignment of the color images, and the ultimate printed composite color image will be degraded. One way to adjust the timing is to use belt edge position detectors for detecting starting of scanning of laser beams for exposure. The detectors are disposed on the rear face side in the proximity of an edge of the photo receptor belt on the laser scanning starting side such that signals for providing timings at which scanning of image signals are to be started on the photo receptor belt at timings at which the exposure laser beams are intercepted by the photo receptor belt after the exposure laser beams pass the belt edge position detector are outputted from the belt edge position detectors. A color image formation apparatus of the type described is disclosed, for example, in Japanese Patent Laid-Open No. Hei 4-274467.
In the conventional color image formation apparatus, however, the laser beams must be irradiated upon locations outside an image writing range on the photo receptor belt. Therefore, where the color image formation apparatus has such a large size that it handles a paper sheet of the A3 size or the like, it is very difficult to form the laser units for it.
In order to allow a laser beam to be irradiated upon a location outside an image writing range, some color image formation apparatus employs an additional mirror.
However, in order to allow a laser beam to be irradiated directly upon a location outside an image writing range without using an additional mirror, a special lens must be provided. In order to irradiate a laser beam directly upon a location outside an image writing range, a corner portion M of a reflecting surface of a polygon mirror as indicated in
FIG. 7
is used. However, reflected light from the corner portion of the polygon mirror is liable to have a low intensity. The special lens mentioned above is a lens designed to restrict the diameter of the laser beam and direct the laser beam so as to be irradiated upon the belt edge position detector at a sufficiently high intensity.
The conventional color image formation apparatus described above is disadvantageous in that it is complicated in structure, difficult to produce and high in production cost because it employs a special lens.
Further, even if it is tried to start writing at a fixed position from an edge of the photo receptor belt after the edge is detected on the basis of timing signals from a clock generator, the writing start positions for the different colors may be displaced from each other by an amount corresponding to one clock pulse unless video clock signals for the different colors are synchronized with each other. Consequently, the conventional color image formation apparatus described above is disadvantageous also in that out-of-alignment of color images may not be eliminated and a color image of a high quality cannot be obtained.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photo receptor belt edge detection apparatus by which out-of-alignment of color images which arises from displacement of scanning start positions for different colors on a photo receptor belt can be eliminated with a simple construction to allow superposition of color images to be performed with a high degree of accuracy.
The present invention provides a photo receptor belt edge detection apparatus for a color image formation apparatus wherein a traveling photo receptor belt is exposed to scanning light beams from a plurality of exposure light sources of different image formation units for different colors in a direction perpendicular to the traveling direction of the belt to form color separation images which are superposed on the photo receptor belt to form a composite color image. The invention employs a plurality of belt edge detecting light sources for each of the color separation image formation units, and a plurality of belt edge detecting light sensor sections for detecting positions of an edge of the photo receptor belt as light beams emitted from the respective belt edge detecting light sources are intercepted by the photo receptor belt. The resulting edge detection signals, are used to start the riding of the image data for the respective color separation images after a fixed interval of time following receipt of the corresponding belt edge detection signal.
Preferably, each of the image formation units for the different colors includes clock synchronization means for synchronizing a video clock signal to be used to output image data with the detection signal from a corresponding one of the belt edge detecting light sensor sections.
Preferably, the belt edge detecting light sources and the belt edge detecting light sensor elements are disposed in an opposing relationship to each other on extension lines of scanning lines of the scanning light beams of the exposure light sources in the image formation units for the different colors. Further preferably, the belt edge detecting light sources and the belt edge detecting light sensor sections are disposed in an opposing relationship to each other across the photo receptor belt such that opposing faces thereof extend over both of an inner region on the inner side with respect to the edge of the photo receptor belt and an outer region on the outer side with respect to the edge of the photo receptor belt. Further, each of the belt edge detecting light sources may include a plurality of light emitting diodes disposed in a main scanning direction which is an exposure light scanning direction of a corresponding one of the exposure light sources, and the light emitting diodes in each of the belt edge detecting light sources successively emit light. Furthermore, each of the belt edge detecting light sensor sections may include a photodiode which receives the light successively emitted from the plurality light emitting diodes to detect the position of the edge of the photo receptor belt. Alternatively, each of the belt edge detecting light sensor sections may include a CCD sensor including a plurality of CCD sensors and receives, by means of the plurality of CCD sensors, the light successively emitted from the plurality of light emitting diodes to detect the position of the edge of the photo receptor belt.
With the photo receptor belt edge detection apparatus, even if the photo receptor belt inadvertently moves in the laterally leftward or rightward direction, writing of video signals for the different colors on the photo receptor belt is started normally at the same distance from t
Le N.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Pham Hai C.
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