Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2000-11-06
2002-06-25
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S134000, C347S137000, C347S258000, C359S819000
Reexamination Certificate
active
06411325
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to optical systems, and more particularly to an optical unit that scans a beam radiated from a light source in a predetermined direction. The present invention lends itself, for example, to a scanning optical system for an electrophotographic recording device, and optical disk unit.
The “electrophotographic recording device” by which we mean is a recording device employing the Carlson process as described in U.S. Pat. No. 2,297,691, and denotes a nonimpact image-forming device that provides a recording by depositing a developing agent as a recording material on a recordable medium (e.g., printing paper, and OHP film). The electrophotographic recording device is typified by a laser printer, and is broadly applicable not only to a discrete printer, but also generally to an apparatus having a printing function such as a photocopier and a facsimile unit. The scanning optical system is typically a unit that includes a variety of light sources (e.g., a semiconductor laser, a He—Ne gas laser, a Ar gas laser, and a He—Cd gas laser), a collimating lens, a rotating mirror, an f-è lens, a cylinder lens, etc., serving to form a desired latent image on a photosensitive body.
A laser printer as an example of the electrophotographic recording device has characteristics such as an excellent operability and cost efficiency, and high-quality image formation. In addition, due to a reduced vibration and noise during printing, the use of the laser printer for computer's output devices, facsimile units, photocopiers, etc. has spread steadily, with the recent development of office automation.
The laser printer generally includes a pre-charger, a photosensitive body (e.g., drum and belt), an optical unit, a development device, a transfer device, and a fixing device. The pre-charger electrifies the photosensitive body uniformly (e.g., at −600V). The optical unit forms a latent image by exposure to light on the photosensitive body charged by the pre-charger. To be more specific, the optical unit irradiates a light from the light source on an area, and varies a potential on the irradiated area, for example, to −50V or so, to form an electrostatic latent image on the photosensitive body. The latent image is thereafter visualized into a toner image by the development device. The transfer device, which employs a corona charger for example, transfers the toner image onto the recordable medium or printing paper. The fixing device fixes the toner image that has been transferred on the printing paper, and the printing paper is then ejected.
The optical unit typically includes a light source section, a polygon mirror (rotating mirror), a lens system comprised of an f-è lens and a cylinder lens, a print start detector section (hereinafter referred to as BD sensor), and other necessary mirrors. These components are secured with a mounting part on a bottom surface of a housing, which is sometimes called optical box or optical base.
The light source section includes a light source, a collimating lens, and optionally a cylindrical lens. As the light source, for example, a semiconductor laser is used. The semiconductor laser irradiates a laser beam at a spreading angle from a point light source, so that the longer the radiating distance is, the wider the laser beam spreads out from the light source as a vertex of cone. The collimating lens, which is located near the light source, collimates the laser beam to make a parallel beam. The cylindrical lens subsequently forms the beam that has passed through the collimating lens into a beam converging in one direction. In order to achieve a large exposure area, high quality and fast writing action onto the photosensitive body, the number of semiconductor lasers to be provided is plural, and the equal number of collimating lenses, etc. is provided accordingly.
The polygon mirror, which is a deflector taking on a rotary polyhedron mirror, changes a laser beam traveling direction, and lets the laser beam scan. The lens system is provided to correct curvature, and to ensure constant velocity. The BD sensor detects a laser beam through a mirror, and provides timing for a print start.
In operation of the optical unit, the laser beam irradiated from the light source is collimated via the collimating lens. Thereafter, the laser beam is reflected by the rapidly rotating polygon mirror, and passes through the lens system, to correct curvature. The laser beam that has passed through the f-è lens passes through the cylinder lens while being detected by the BD sensor to provide print timing, scans the photosensitive body for a desired area to be exposed, and forms a latent image.
In order to securely form a high-quality latent image on the photosensitive body, the laser beam needs aligning with each optical axis of the collimating lens, the f-è lens, and the cylinder lens. A misalignment between the beam and each optical axis would lead to a shift of the beam in a sub-scanning direction. The shift of the beam in the sub-scanning direction would make the BD sensor unable to detect the beam, and result in varied pitches between the beams when the light source is made up of two beams. If the BD sensor cannot detect the beam, the print timing cannot be provided, and thus printing operations become impossible. Moreover, the varied pitches between the beams would, for example, thicken contours of the latent image, and deteriorate a print quality.
However, a conventional optical unit disadvantageously undergoes a thermal expansion by heat produced in the optical unit and other printer components during continuous operations of a light source, a lens system, or the like, and causes a misalignment between the beam and each optical axis. The heat is derived from heat sources such as a fixing device, a motor used for conveying a recordable medium, heat producing printed boards of various kinds, and a motor used for rotating a polygon mirror. Resultantly, temperature in the optical unit rises from room temperature (approximately 20° C.) to approximately 60° C., and the components in the optical unit thermally expand. Since the light source section and the lens system are different from each other in thermal expansion amounts due to differences in materials and shapes, the beam and each optical axis in the optical unit, which are properly aligned with each other in an initial state, would become misaligned as operations proceed. The present inventors and other colleagues, having assiduously considered a method of correcting the misalignment between the beam and each optical axis, have consequently put a focus on a method of mounting components in the conventional optical unit.
Referring now to
FIG. 13
, a description will be given more specifically of a structure of the conventional optical unit.
FIG. 13
is a schematic perspective view showing main components in the optical unit
100
B. As shown in the drawing, the optical unit
100
B includes a light source section
10
B, a polygon mirror
20
B, an f-è lens
30
B, and a cylinder lens
40
B. The optical unit
100
B is optically connected with a photosensitive drum
202
. These components
10
B,
30
B, and
40
B are respectively mounted on a base or housing
70
B via mounting parts
102
B through
106
B. The optical unit
100
B has a two-beam structure in which two light sources are provided.
A description will now be given of how the components
10
B,
30
B, and
40
B are mounted with reference to
FIGS. 14 through 16
.
FIG. 14
is a front view, side view, and exploded side view of the light source section
10
B as viewed from a direction C in FIG.
13
.
FIG. 15
is a front view of the f-è lens
30
B as viewed from a direction A in FIG.
13
.
FIG. 16
is a front view of the cylinder lens
40
B as viewed from the direction A in
FIG. 13. A
dash-dot line in each figure represents the optical axes.
As shown in
FIG. 14
, the light source section
10
B includes a semiconductor laser
12
B as a light source, a collimating lens
11
B that collimates a laser light
Matsushita Yukihiro
Sugano Takao
Armstrong Westerman & Hattori, LLP.
Fujitsu Limited Kawasaki
Lee Susan S. Y.
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