Raster output scanner with a field replaceable collimator...

Details Raster output scanner with a field replaceable collimator... Raster output scanner with a field replaceable collimator...

1997-11-25

2001-01-02

Phan, James (Department: 2872)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S216100, C359S217200, C359S641000, C359S829000

Utility Patent

active

06169623

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to raster scanning systems and more particularly, to a raster output scanner which utilizes a collimator assembly which can be replaced in the field at a customer location without disassembling the raster output scanner and sending it back to the manufacturer for replacement.
Typically, a laser printer utilizes a raster output scanner. Referring to
FIG. 1
, there is shown a tangential (fast-scan) view of the raster output scanner
10
of a printing system. The raster output
10
utilizes a laser light source
12
, a collimator
14
, mirrors
16
and
18
, pre-polygon optics
20
and
22
, mirror
24
a multi-faceted rotating polygon mirror
26
as the scanning element, post polygon optics
28
, mirror
30
and a photosensitive medium (photoreceptor)
32
.
The laser light source
12
sends a light beam
34
to the rotating polygon mirror
26
through the collimator
14
and the pre-polygon optics
20
and
22
. Mirrors
16
,
18
and
24
fold and redirect the light beam
34
prior to the scanning polygon
26
and mirror
30
folds and redirects the light beam
34
after the scanning polygon
26
. Mirror
30
is slanted to redirect the light beam
34
outside of the ROS housing onto the photoreceptor
22
to scan a line S.
The collimator
14
collimates the light beam
34
and the pre-polygon optics
20
focuses the light beam
34
in the sagittal or cross-scan plane onto the rotating polygon mirror
26
. However, since this system is an overfilled system, the light beam stays collimated in the tangential plane while striking the polygon mirror
26
. The facets
36
of the rotating polygon mirror
26
reflect the light beam
34
and also cause the reflected light beam
34
to revolve about an axis near the reflection point of the facet
36
. The reflected light beam
34
is utilized through the post polygon optics
28
to scan the photoreceptor
32
.
Typically, all the above optical elements except the laser light source
12
and the collimator
14
are placed in a Raster Output Scanner (ROS) housing
38
. The laser light source
12
and the collimator
14
are placed in a collimator assembly
40
which is mounted onto the ROS housing
38
.
Referring to
FIG. 2
, there is shown an isometric view of the collimator assembly
40
and a portion of the ROS housing
38
of FIG.
1
. Referring to Both
FIGS. 1 and 2
, ROS housings
38
is usually made of plastic or metal and has an opening
42
for receiving a light beam from the laser light source
12
. The collimator assembly
40
holds the laser diode
12
and the collimator
14
. The base
46
of the collimator assembly
40
is mounted on wall
44
of the housing
38
in such a manner that the axis
48
of the collimator assembly coincides with optical path
35
. The optical path
35
is the optical axis of the optical elements within the ROS housing
38
. The laser diode
12
emits a light beam
34
and collimator
14
collimates and sends the light beam
34
into the ROS housing
38
through the opening
42
. Within the ROS housing
38
, the light beam
34
travels along the optical path
35
.
During manufacturing, after the collimator assembly
40
is mounted on the ROS housing
38
, the position of the light beam
34
from the laser diode has to be adjusted to overlap the optical path
35
and the intensity of the light beam
34
has to be adjusted to match a required discharge level of the photoreceptor used in that specific printer. Adjusting the position and the intensity of the light beam
34
are very critical in the print quality. For example, if the light beam
34
does not travel on the optical path
35
, the light beam striking the photoreceptor might be out of focus which causes the print to be blurred. In addition, if the intensity level of the light beam happens to be over or under the required level, the print will be darker or blank respectively.
The above adjustments are done based on the location and the characteristics of the laser diode. The pointing of a laser diode with respect to the optical path
35
depends on the mounting of the collimator assembly to the ROS housing. Furthermore, characteristics of each individual laser diode is different from characteristics of other laser diodes. Therefore, in order to adjust the intensity of a laser diode, the laser driving current has to be adjusted. As a result, if a laser diode of a printer needs to be replaced, the whole ROS housing is used to readjust a new replacement collimator assembly.
Therefore, in order to replace a laser diode, the ROS housing, including the collimator assembly, has to be dismounted from the printer and sent back to the manufacturing. Since the ROS housing holds expensive optical elements, it is desirable not to transfer it back to manufacturing to prevent any damage to the optical elements. Furthermore, transferring the ROS housing to the manufacturing for repair or replacement can be very costly to the user in terms of loss of productivity. Therefore, it is advantageous to replace the collimator assembly in the field instead of sending the ROS housing back to the manufacturer.
It is an object of this invention to design a collimator assembly which can be replaced, aligned and adjusted in the field.
SUMMARY OF THE INVENTION
The present invention is directed to a design implementation of raster output scanner with a field replaceable collimator assembly containing a laser diode. The collimator assembly of this invention, which acts as a pointing device, is removeably mounted on a raster output housing. The design of the collimator assembly and the raster output housing both have aligning means and securing means designed in such a manner that once the aligning means are engaged, the collimator assembly can be slightly moved in the tangential plane to align the securing means. Once the securing means are engaged, the light beam from the collimator is in alignment with an optical path within the raster output housing.


REFERENCES:
patent: 5255115 (1993-10-01), Kikuchi
patent: 5381438 (1995-01-01), Guo et al.
patent: 5400133 (1995-03-01), Hinton et al.
patent: 5684524 (1997-11-01), Hokamura
patent: 5701191 (1997-12-01), Iwasaki
patent: 5969843 (1999-10-01), Naiki et al.
patent: 0 608 901 A2 (1994-08-01), None
patent: 04285976 (1992-10-01), None
patent: 04328515 (1992-11-01), None
patent: 07261115 (1995-10-01), None

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