Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1997-08-28
2001-06-05
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S250000
Reexamination Certificate
active
06243123
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a light beam scanning apparatus for simultaneously scanning and exposing a single photosensitive drum with a plurality of laser beams, thereby to form a single electrostatic latent image on the photosensitive drum, and an image forming apparatus such as a digital copying machine or a laser printer using the light beam scanning apparatus.
In recent years, various digital copying machines have been developed in which image formation is performed by scanning and exposing with a laser beam and electronic photographing processing.
More recently, in order to obtain higher image forming speed, developments have been made to a digital copying machine adopting a multi-beam method in which a plurality of laser beams are generated and scanning is simultaneously carried out for a plurality of scanning lines with use of a plurality of beams.
This kind of digital copying machine which adopts such a multi-beam method comprises a plurality of laser oscillators for generating laser beams, a multi-face rotation mirror such as a polygon mirror for reflecting the laser beams generated by the plurality of laser oscillator toward a photosensitive drum to scan the photosensitive drum with the laser beams, and an optical unit serving as a light beam scanning device consisting mainly of a collimator lens and an f-&thgr; lens.
However, in the structure of a conventional optical unit, it is very difficult to obtain an ideal positional relationship between a plurality of light beams on a photosensitive drum (or a surface to be scanned). In order to obtain an ideal positional relationship, respective components as well as assembling thereof require high accuracy, and hence the cost of the device is increased.
Even if an ideal positional relationship is obtained, the shape of a lens may vary slightly or the positional relationship between respective components may vary slightly due to circumferential changes, such as changes in temperature and humidity or time-based changes. Consequently, the positional relationship between light beams varies, and as a result a high quality image cannot be formed. Therefore, to construct this kind of optical system, it is necessary to adopt a structure and components which are strong against changes as described above. In particular, as for lenses, a glass lens which is strong against circumferential changes and time-based changes is expensive so that the cost of the device is increased.
In the following, defects in the multi-beam method, which are caused when an image is formed with light beams whose passing positions are erroneously dislocated, will be explained with reference to
FIGS. 32A and 32B
and
FIGS. 33A and 33B
.
For example, in a case where character “T” shown in
FIG. 32A
is formed, an image as shown in
FIG. 32B
is formed when a passing position of a light beam is erroneously dislocated from a predetermined position. In the example of this figure, the passing position of a light beam b is shifted from its predetermined position so that the distance between light beam a and b is reduced while the distance between light beam b and c is increased, among four light beams a and d used. In other words, the dot interval changes in the sub-scanning direction.
FIG. 33A
shows an example of an image in which emission timings of respective light beams are not controlled correctly. As is apparent from this figure, the image forming position in the main scanning direction is dislocated so that a longitudinal line cannot be formed straight. That is, the dots are shifted from each other in the main scanning direction.
FIG. 33B
shows an image in which neither the passing positions of light beams not the emission timings are controlled correctly, defects in an image appear both in the sub-scanning direction and in the main scanning direction.
Thus, when an image is formed in a multi-beam method, light beam passing positions in the sub-scanning direction must be controlled so as to be arranged at predetermined intervals, and the emission timings of respective light beams must be controlled so as to align the image forming position in the main scanning direction.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a light beam scanning apparatus and an image forming apparatus using the light beam scanning apparatus, wherein the passing position of the beam can be precisely detected with no special precision in assembling a optical system, and the position of the beam can be controlled at a predetermined position, even if some change occurs in the structure of the optical system due to a variation in ambience or a variation with the passing of time.
Another object of the invention is to provide a light beam scanning apparatus and an image forming apparatus using the light beam scanning apparatus, wherein even in a case where plural light beams are used, the passing positions of the beams can be precisely detected with no special precision in assembling a optical system, and the positional relationship among the beams on a scan surface to be scanned can be controlled in an ideal condition at all times.
In order to achieve the above object, according to one aspect of the present invention, there is provided a light beam scan apparatus comprising: light beam generating means for generating a light beam; scan means for reflecting the light beam, generated by the light beam generating means, to a scan surface to be scanned, and for scanning the scan surface in a main scan direction and a sub-scan direction by means of the light beam; a plurality of light detection means (SB to SF), arranged near the scan surface in the sub-scan direction, for receiving the light beam and outputting a corresponding signal; position determination means for determining, on the basis of the signal output from the light detection means, the position in the sub-scan direction of the light beam scanned by the scan means; and control means for controlling the position in the sub-scan direction of the light beam scanned by the scan means on the scan surface at a predetermined position, on the basis of the determination result of the position determination means.
In general, a plurality of light detection means, provided in a light beam scanning apparatus, for confirming a beam scan position are arranged at an angle to a sub-scan direction. In the present invention, however, the plural light detection means are linearly arranged in the sub-scan direction at intervals of, e.g. 42.3 &mgr;m. Thus, the light detection means can be assembled in such an apparatus with a beam scanning apparatus, as an image forming apparatus, with no special precision. The passing position of the beam can be precisely detected, and the position of the beam can be controlled at a predetermined position, even if some change occurs in the structure of the optical system due to a variation in ambience or a variation with the passing of time.
Besides, the plurality of light detection means comprise a plurality of first light detection means arranged at regular intervals in the sub-scan direction of the light beam, and two second light detection means arranged outside both ends of the first light detection means in the sub-scan direction. Each of the second light detection means is much greater in size than each of the first light detection means. The second light detection means is provided to detect the beam position, even when the position of the beam in the sub-scan direction deviates greatly from its normal position.
According to another aspect of the present invention, there is provided a light beam scanning apparatus according wherein a plurality of the light beam generating means are provided, and the scan means includes means for reflecting the light beams, generated by the plural light beam generating means, to the scan surface, and for scanning the scan surface in the main scan direction and sub-scan direction by means of the light beams. Middle positions between adjacent two of the light detection means coincide with target positions
Ide Naoaki
Komiya Kenichi
Miura Kunihiko
Sakakibara Jun
Tanimoto Koji
Foley & Lardner
Kabushiki Kaisha Toshiba
Le N.
Nguyen Lamson D.
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