Beam scanning system adopting deflection disc

Details Beam scanning system adopting deflection disc Beam scanning system adopting deflection disc

1999-11-09

2001-09-18

Henry, Jon (Department: 2872)

Optical: systems and elements

Holographic system or element

Using a hologram as an optical element

C359S016000

Reexamination Certificate

active

06292278

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to beam scanning systems for use in electrophotographic type image forming apparatuses, and more particularly, to a beam scanning system for diffracting and deflecting beams emitted from light sources using a diffractive deflection disc, in which the deflection disc has double-sided diffraction patterns to increase a deflection angle, and simultaneously to avoid bowing of the beams.
2. Description of the Related Art
In general, beam scanning systems are employed by electrophotographic image forming apparatuses for use in forming an electrostatic latent image on a photosensitive medium such as a photoreceptor web by, for example, scanning beams emitted from a laser scanning unit and a light source. Recently, a multi-beam scanning system which diffractingly deflects beams emitted from light sources by adopting a rotary deflection disc, instead of by adopting a rotary polygon used in a conventional beam scanning system, has been introduced.
FIG. 1
shows a schematic configuration thereof.
Referring to
FIG. 1
, the beam scanning system includes a light source
10
and a deflection disc
11
rotatably mounted over the light source
10
. The deflection disc
11
rotates rapidly by being coupled to a driving motor
12
, and a plurality of sectors having hologram patterns are formed on the surface thereof.
A beam emitted from the light source
10
is diffracted by the hologram patterns while passing through a rotating deflection disc
11
. Referring to
FIG. 2
, because hologram patterns
11
a
are formed to have different diffraction angles according to the rotation angle of the deflection disc
11
, beams that are emitted from the same light source
10
, are diffracted at different angles with the rotation of the deflection disc
11
, to create a single scanline of the beams. The beams diffracted by the diffraction disc
11
are deflected by a plurality of reflecting mirrors
13
and
14
, so that its traveling direction is changed.
The reflected beams come to pass through a beam correction means. In general, a condensing mirror
15
for condensing and reflecting the beam, and a hologram optical element
16
for diffractingly transmitting the beam to direct the beam toward a photosensitive medium (not shown) such as a photoreceptor web. Alternatively, the beam correction means may be replaced with an F-&thgr; lens (not shown) that corrects the focal position and scanwidth of the beam. The F-&thgr; lens corrects aberrations of the beam scanned in a primary scan direction and sets the form of the beam as the deflection disc
11
rotates.
Through the above operations, beams emitted from the light source
10
can form a scanline on the photoreceptor web in the primary scan direction, that is, in a direction perpendicular to the traveling direction of the photoreceptor web.
In the beam scanning system having the above configuration, there are many difficulties in manufacturing the deflection disc
11
. That is, due to a rapid rotation of the deflection disc
11
for operation, its operation becomes less stable with an increase in the size of the deflection disc
11
. However, because the deflection disc
11
needs such high-density hologram patterns
11
a
to diffract beams, there is a limit to reducing the size of the deflection disc
11
. As the size of the deflection disc
11
becomes smaller, a more precise processing technology is required to form the hologram pattern
11
a
thereon.
Another problem of the conventional beam scanning system adopting the deflection disc mentioned above is bowing of the scanline, where a straight scanline cannot be created because beams are diffracted by the rotation of the deflection disc
11
while the light source is fixed. Thus, the conventional beam scanning system needs an external optical device, that is, a bowing correction reflecting mirror, to correcting bowing. If a bowing generating source does not arise from the deflection disc or if the bowing can be corrected by the deflection disc itself, the number of parts for a scanning system can be reduced.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a beam scanning system adopting a diffractive reflection disc, in which the deflection disc has hologram patterns on both upper and lower surfaces thereof, providing an effect as if a high hologram pattern is formed thereon, and simultaneously the bowing of the scanline, which occurs with the rotation of the deflection disc, can be corrected by the hologram pattern.
To achieve the above object of the present invention, there is provided a beam scanning system comprising: a light source; a deflection disc rotatably installed over the light source, having a hologram pattern on each of the upper and lower surfaces thereof, for diffracting beams emitted from the light source; and a plurality of mirrors for reflecting beams that have been diffracted by the deflection disc, to change the paths of the beams. Preferably, beams emitted from the light source are primarily diffracted by the lower hologram pattern, and then diffracted again by the upper hologram pattern.


REFERENCES:
patent: 4923262 (1990-05-01), Clay
patent: 5182659 (1993-01-01), Clay et al.
patent: 5550655 (1996-08-01), Kayashima et al.
patent: 61-141418 (1986-06-01), None
patent: 3-198020 (1991-08-01), None
patent: 4-166908 (1992-06-01), None
patent: 4-289814 (1992-10-01), None
patent: 5-159316 (1993-06-01), None

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