Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-09-20
2003-04-29
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S235000, C250S236000, C359S197100, C359S201100, C359S206100, C359S216100
Reexamination Certificate
active
06555810
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an optical scanning device employed in an optical writing unit of a laser printer, a laser copier or the like, and deflecting a laser light emitted from a laser light source and thus scanning a surface to be scanned while forming a beam spot on the surface to be scanned, and, in particular, an optical scanning device employing a plurality of optical scanning units each including a light source, a first optical system, a deflector and a second optical system, and continuously scanning one surface to be scanned through coordinated movements of the respective optical scanning units.
2. Description of the Related Art
Recently, high density writing, high-speed writing and miniaturization are demanded for laser printers, laser copiers and so forth. Accordingly, for optical scanning devices which occupy a large space from a laser light source to a surface to be scanned, it is demanded to deal with high density writing, high-speed writing and miniaturization.
However, an optical scanning device, such as for example including a single laser light source which emits a light flux and a single deflector which deflects the light flux a surface to be scanned is scanned (raster-scanned) by means of a beam spot, and the optical scanning device needs to deflect the light flux extending from a deflector to the surface to be scanned through a wide range of the surface to be scanned. Because there is a limit to the angle by which the light flux extending from the deflector to the surface to be scanned is deflected for scanning, long distance is needed between the deflect and surface to be scanned. Thus, a large is needed in the optical scanning device. Accordingly, it is difficult to miniaturize the optical scanning device.
Further, it is necessary to reduce the diameter of a beam spot to deal with high-density writing. For this purpose, it is necessary to design the optical system subsequent to the deflector to have a small focal length. Also from this point, it is difficult to achieve high-density writing using a single laser light source and a single deflector.
An optical scanning device in the related art will now be described with reference to a figure.
FIG. 1
shows a configuration of the optical scanning device in the related art.
As shown in the figure, the optical scanning device
100
includes a light source
1
such as for example a semiconductor laser which emits a divergent laser light flux, a coupling lens
2
which is for example a collimator lens to transform the divergent light flux emitted from the light source
1
into an approximately parallel light flux, a stop
3
which reduces the diameter of the light flux made to be approximately parallel by the coupling lens
2
and cuts an unnecessary flux portion, a line-image forming optical system
4
which, as a cylindrical lens for example, has a refracting power in sub-scanning direction, and a mirror
5
which bends the light path of the light flux exiting from the line-image forming optical system
4
by reflecting it and thereby directs it to a deflection reflective surface
6
a
of a deflector
6
. The deflector
6
deflects in a main scanning direction the light flux so as to become like a line, long in the main scanning direction by the line-image forming optical system
4
and incident on the deflection reflective surface
6
a
by rotating the deflector at a uniform angular velocity. An f&thgr; lens
7
corrects the light path of the light flux deflected by the deflector
6
for linearly scanning a photosensitive body
9
. A long-dimensional lens
8
corrects the surface inclination of the light flux occurring from the deflection reflective surface
6
a
. For example, when photosensitive body
9
, which is a surface to be scanned, is scanned by a beam spot formed of the deflected light flux, a synchronization detecting sensor
12
is used for establishing synchronization between the light flux emitted from the light source
1
and the rotation angle of the deflector
6
based on the incident light flux.
The light source
1
, coupling lens
2
, stop
3
, line-image forming optical system
4
and mirror
5
constitute a scanning input optical system
15
. Further, the f&thgr; lens
7
and long-dimensional lens
8
constitute a scanning and imaging optical system
18
.
The optical scanning device
100
shown in
FIG. 1
operates as follows:
A divergent light flux
20
emitted from the light source
1
is transformed into an approximately parallel light flux
20
a
by the coupling lens
2
, has an unnecessary light flux portion thereof cut by the stop
3
, is condensed in sub-scanning direction by the line-image forming optical system
4
, is reflected by the mirror
5
, and, thus, is incident on the deflection reflective surface
6
a
of the deflector
6
becoming like a line long in.main scanning direction.
The deflector
6
rotates at the uniform angular velocity in direction of arrow
30
, and the entrance angle and exit angle of the incident light flux
20
a
with respect to the deflection reflective surface
6
a
change with the rotation of the deflector
6
. Accordingly, the incident light flux
20
a
exits therefrom as the light flux
20
b
→
20
c
→
20
d
in the stated order as a result of being deflected by the deflection reflective surface
6
a
in main scanning direction according to the rotation of the deflector
6
.
Each light flux
20
b
,
20
c
,
20
d
exiting from the deflector
6
has the light path thereof corrected by the f&thgr; lens
7
so as to scan the photosensitive body
9
linearly in direction indicated by arrow
50
, and has the surface inclination of the deflection reflective surface
6
a
corrected by the long-dimensional lens
8
.
Each light flux
20
b
,
20
c
,
20
d
corrected by the f&thgr; lens
7
and the long-dimensional lens
8
forms a beam spot on the-photosensitive body
9
.
The synchronization detecting sensor
12
detects, for example, the light flux
20
e
exiting from the deflector
6
, compares the timing of the thus detected light flux with the timing of the predetermined light flux emitted from the light source
1
, and eliminates the difference therebetween. Thereby, synchronizes the rotational angle of the deflector
6
with the light flux emitted from the light source
1
.
In order to miniaturize an optical scanning device such as that
100
shown in
FIG. 1
, for example, as disclosed in Japanese Laid-Open Patent Application No. 61-11720, two deflectors are used, thereby a scanning length to be scanned by each deflector is reduced, and miniaturization is achieved.
However, in such a method, as a result of two deflectors being employed, it is important to secure continuity between light fluxes (scanning laser beams) exiting from the respective deflectors, precisely. However, Japanese Laid-Open Patent Application No. 61-11720 does not clearly disclose how to secure continuity between the light fluxes precisely.
On the other hand, Japanese Laid-Open Patent Application No. 10-68899, for example, discloses a method in that two sets of deflectors and optical components for the respective deflectors are disposed stepwise, and, also, light fluxes from the respective deflators are made to be continuos by a beam splitter, and, thereby, continuity between the light fluxes is precisely secured.
However, in such a method, a beam splitter is needed as an extra component, and, also, a high level of position adjustment technology and so forth are needed for securing continuity between light fluxes from respective sets of deflectors and optical components disposed stepwise through the beam splitter.
Accordingly, it is difficult to actually manufacture it.
Further, in order to further miniaturize an optical scanning device, it is necessary to secure continuity between light fluxes from respective ones of more than two sets of deflectors and optical components through a beam splitter. However, it is further difficult to actually manufacture it because a further high level of position adjust
Allen Stephone B.
Glass Christopher W.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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