Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2002-03-08
2004-09-07
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S132000
Reexamination Certificate
active
06788330
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a clock-generating circuit and an image-forming apparatus employing f&thgr; lens in an optical writing section, and specifically relates to a combination of an image-forming apparatus and a clock-generating circuit, which makes it possible to reduce influence to the image quality caused by property errors of the f&thgr; lens.
In conventional image-forming apparatus, an image is formed on an image-bearing member rotating in a sub-scanning direction by scanning a laser beam, modulated in response to image data, in a main-scanning direction. In this operation, the laser beam is modulated in response to the image data in reference to reference signals called as dot clock pulses.
Incidentally,
FIG. 7
shows perspective view of a configuration of the optical writing section employing a laser beam in the image-forming apparatus as described in the above. As shown in
FIG. 7
, laser diode
470
(LD) emits the laser beam based on the laser driving signals generated by circuit section
400
.
Further, the laser beam, emitted by laser diode
470
and having been passed through collimator lens
491
and cylindrical lens
492
, is deflected for scanning by polygon mirror
493
, and scans image-bearing member
1
for writing, after passing through f&thgr; lens
494
so as to adjust the scanning velocity at constant and cylindrical lens
495
. In addition, a part of the laser beam deflected by polygon mirror
493
is led to index sensor
412
for detecting the timing.
First Problem
In case of the image-forming apparatus, which employs the laser beam as writing means, the expansion of the casing mainframe caused by increase of its temperature influences various kinds of optical elements. For instance, a certain optical property would be varied by the change of a length between lenses.
Further, since general f&thgr; lenses are made of plastic material with mold by employing the plastic molding process, refractive indexes of them are apt to vary with the change of ambient temperature. When the ambient temperature changes under the normal operating conditions of the apparatus, f&thgr; property change (f&thgr; property error) of around ±0.8% (a uniformity of scanning velocity of the laser beam on the surface of the image-bearing member) would occur as shown in FIG.
8
.
Second Problem
To attain the f&thgr; property, which sufficiently makes the scanning velocity of the laser beam on the surface of image-bearing member uniform, f&thgr; lens should be shape in a complicated spherical or aspherical lens. It is impossible, however, to design such f&thgr; lens that has completely no f&thgr; property error. Accordingly, f&thgr; property error of around ±0.1% still remains even in the design stage of f&thgr; lens, as shown in FIG.
9
.
Further, since the f&thgr; property error has dependability on wavelength of the laser beam, the f&thgr; property is attained by reducing various kinds of aberrations at a predetermined wavelength of the laser beam. Accordingly, since the wavelengths of the laser beams emitted by laser diodes of the same kind would slightly vary relative to each other due to the slight differences between individualities of the laser diodes, the deviation from the predetermined wavelength in each of the laser diodes would result in the f&thgr; property error. In order to strictly control the wavelengths of the laser beams emitted by laser diodes, however, it is necessary to select usable laser diodes out of a large amount of laser diodes, resulting in increase of the production cost of the apparatus concerned, which has been one of problems. For instance, in a color image-forming apparatus, which provides four stages of image-writing units corresponding to four primary colors, there happens a problem that images corresponding to four primary colors deviate relative to each other due to occurrence of the f&thgr; property error in each of the four image-writing units, unless the wavelengths of the laser beams, emitted by the laser diodes employed in the four image-writing units, are completely coincided each other.
Third Problem
When the f&thgr; lenses are manufactured through the plastic molding process, which employs molds, refractive indexes of the manufactured f&thgr; lenses vary with the variations of the molds. The molds would vary one by one, when the f&thgr; lenses are simultaneously manufactured in parallel by employing a plurality of molds, or when an old mold is replaced by a new mold every predetermined period of time, etc. Generally speaking, as shown in
FIG. 10
, a variation between molds would result in f&thgr; property change (f&thgr; property error) of around ±0.1% (a uniformity of scanning velocity of the laser beam on the surface of the image-bearing member). In order to suppress the f&thgr; property error, the variations between the molds should be strictly controlled, resulting in increase of manufacturing cost of the molds as well as increase of the production cost of the apparatus concerned, which has been another one of problems.
Forth Problem
In the f&thgr; lens-manufacturing site, sometimes, variations of refractive indexes of the f&thgr; lenses are caused by the variations of manufacturing processes corresponding to differences of manufacturing dates of them, etc. In order to suppress the f&thgr; property error, the variations between the manufacturing processes should be strictly controlled, resulting in increase of manufacturing cost of the f&thgr; lens as well as increase of the production cost of the apparatus concerned, which has been another one of problems.
SUMMARY OF THE INVENTION
To overcome the abovementioned drawbacks in conventional image-forming apparatus, it is an object of the present invention to provide a clock-generating circuit and an image-forming apparatus employing the polygon mirror as writing means, which make it possible to reduce the influence to the image quality, caused by the f&thgr; property error.
Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by clock-generating circuits and image-forming apparatus described as follow.
(1) A circuit for generating dot clock pulses for driving a light-emitting element employed in an optical-writing section of an image-forming apparatus, comprising: a digital-delay dot clock adjusting section to adjust timings of rising-edges or falling-edges of the dot clock pulses generated by changing a selection for a plurality of delayed-clock pulses, which are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; and a controlling section to control a selecting operation for the plurality of delayed clock pulses, performed in the digital-delay dot clock adjusting section, so as to compensate for a f&thgr; property error of a f&thgr; lens employed in the optical-writing section.
(2) A circuit for generating dot clock pulses for driving a light-emitting element employed in an optical-writing section of an image-forming apparatus, comprising: an index sensor to detect a light-beam, which is emitted from the light-emitting element and is deflected for scanning by a light-scanning device employed in the optical-writing section, and to output an index signal when the index sensor detects the light-beam at an end portion of a main-scanning region scanned by the light-beam; a delay-chain section to generate a plurality of delayed-clock pulses by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; a synchronized clock pulse detecting section to select synchronized delayed-clock pulses, which are synchronized with the index signal, out of the plurality of delayed clock pulses generated in the delay-chain section, and to output a number of delay-stages, which is derived from the synchronized delayed-clock pulses, as synchronizing information; a table memory to store f&thgr; property error information, which represents a f&thgr; property error of a f&thgr; lens employed in t
Morita Shinji
Takaki Kouichi
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
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