Optical scanning unit with rotatable hologram disc

Details Optical scanning unit with rotatable hologram disc Optical scanning unit with rotatable hologram disc

2001-09-21

2003-10-28

Juba, John (Department: 2872)

Optical: systems and elements

Holographic system or element

Using a hologram as an optical element

C359S015000, C359S017000, C359S209100, C235S462340

Reexamination Certificate

active

06639698

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2000-57513, filed on Sep. 29, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical scanning unit, and more particularly, to an optical scanning unit with a rotatable hologram disc having a plurality of concentric holograms formed in a radial direction.
2. Description of the Related Art
Generally, in electrophotographic image forming devices, an optical scanning unit is provided to scan a light beam to a photoreceptive medium to form an electrostatic latent image.
Conventionally, optical scanning units include a light source, a rotary polygonal mirror, and an f-&thgr; lens.
However, more recently it has been suggested that the optical scanning unit could alternatively be implemented with a rotatable hologram disc, for diffractively deflecting a beam emitted from a light source, with its schematic configuration being shown in FIG.
1
.
Referring to
FIG. 1
, the optical scanning unit includes an in-scan corrector hologram
3
, a rotatable hologram disc
4
, a curved mirror
6
, and a cross corrector hologram
7
on a path of a beam emitted from a light source
1
.
The beam emitted from the light source
1
is focused, by the in-scan corrector hologram
3
, to fall on the rotatable hologram disc
4
. The beam incident on the rotatable hologram disc
4
is thereby diffracted, with its bow and aberration being eliminated by the curved mirror
6
and the cross corrector hologram
7
. The beam is then scanned to a photoreceptive medium
8
.
Another example of an optical scanning unit is shown in FIG.
2
. As illustrated in
FIG. 2
, the optical scanning unit includes a rotatable hologram disc
10
and a fixed hologram
20
. A beam
11
emitted from a light source (not shown) is diffracted by the rotatable hologram disc
10
to generate a diffractive beam
12
. The diffractive beam
12
is diffracted again by the fixed hologram
20
to generate a diffractive beam
13
. The diffractive beam
13
is scanned to an image formation region
15
.
In the aforementioned optical scanning units using rotatable hologram discs, the sector size of the disc and the number of sectors are based upon the scan width.
Likewise, in the optical scanning unit using a rotatable polygonal mirror, the mirror size of the rotatable polygonal mirror and the number of its surfaces are also based upon the scan width.
Typically, the optical scanning units have been designed to scan across A4 sized paper (210×297 mm). However, due to recent demands of the market, it is desirable to have an optical scanning unit for A3 sized paper (297×420 mm).
However, to provide the scan width corresponding to the A3 sized paper, the optical scanning unit requires a hologram disc having an increased sector size. That is, as shown in
FIG. 3
, if one sector
4
a
or
10
a
, corresponding to respective discs
4
and
10
of
FIGS. 1 and 2
, provides a scan angle of &thgr;a, an increased sector size is required to extend the scan angle. However, if the sector size is increased, a problem arises in that the number of sectors is reduced, thereby reducing a scan speed. Further, even in the case of a rotatable polygonal mirror (not shown), if the mirror size is increased, the scan speed is reduced. Thus, the scan width cannot be extended while uniformly maintaining the scan speed.
Furthermore, to increase the scan speed, it has been suggested to increase the rotation speed of a motor rotating the rotatable polygonal mirror or the discs
4
and
10
, of respective
FIGS. 1 and 2
. However, with this solution, there exists a technical limitation in increasing the rotation speed of the motor. Moreover, a high speed rotatable motor provided with a high speed fluid/gas bearing is expensive.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an optical scanning unit with a rotatable hologram disc in which a scan width can be extended without reducing a scan speed.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
In order to achieve the above and other objects of the present invention, there is provided an optical scanning unit with a rotatable hologram disc in accordance with the present invention including a light source, a rotatable hologram disc provided with a plurality of holograms, the holograms being formed concentrically along a radial direction to diffract a beam emitted from the light source, a reflecting member that reflects the beam emitted from the light source and diffracted by one of the holograms into another hologram, and a fixed hologram correcting the diffracted beam incident through the rotatable hologram disc to focus it on a scanning object.
Preferably, the rotatable hologram disc includes an inner hologram and an outer hologram which are sequentially formed along a radial direction from the center.
In accordance with one aspect of the present invention, the inner hologram is a transmittance type that transmits and diffracts the beam emitted from the light source while the outer hologram is a reflecting type that reflects and diffracts the beam incident from the inner hologram as reflected by the reflecting member.
In accordance with another aspect of the present invention, the inner hologram and the outer hologram respectively are of a transmittance type to transmit and diffract an incident beam. Also, the optical scanning unit in accordance with another aspect of the present invention further includes a reflecting member reflecting the beam transmitted by the outer hologram into the fixed hologram.
In accordance with still another aspect of the present invention, the inner hologram and the outer hologram, respectively, are of a transmittance type to transmit and diffract the incident beam. Also, the optical scanning unit in accordance with still another aspect of the present invention further includes a reflecting layer formed on a surface of the rotatable hologram disc that is opposite to another surface of the rotatable hologram disc where the outer hologram is formed, to reflect the beam, which is transmitted through the outer hologram, back through the outer hologram.
Further, the inner hologram and the outer hologram may have the same diffractive pattern or different diffractive patterns.


REFERENCES:
patent: 4678263 (1987-07-01), Funato
patent: 5309272 (1994-05-01), Harris
patent: 6046831 (2000-04-01), Eum

Affiliated with

Also associated with

Rating

Optical scanning unit with rotatable hologram disc does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical scanning unit with rotatable hologram disc, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical scanning unit with rotatable hologram disc will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3159113