Note: Descriptions are shown in the official language in which they were submitted.
~1~5~46
BACKGROUND OF THE I~VE~TIO~
. _ .
This invention relates to optical systems and in
particular to a strip scanning optical system for scanning an
object and progressively projecting a composite image of the
same at an image surface, such as a xerographic or other
photosensitive surface in a photocopying proces3.
There are three general types of strip scanning
arrangements known to the prior art. In one~ the optical
system is fixed and the object and photorecptor move relative
to the optics, In the second, the object is fixed and the
optical system and photoreceptor move at appropriate speeds
( relative to the object. In the third, the object is fixed and
i5 scanned by a rotating mirror to relay an image of the object
onto a moving photoreceptor.
Typically, these prior art systems have in common
the fact that they are capable o projecting a usable image
only in one direction o~ scan motionO The return motion,
whether it be return o~ the object, the optics, or the mirror,
projects an image onto the moving photoreceptor which is
disoriented (wrong reading~ and thexefore useless. Accordingly,
- the prior art has variously resorted to flyback arrangements
to minimize the "lost time" involved in the return motion of
the scan mechanism. one system by which to accomplish scanning
in both directions of object reciprocation is shown in U~ S.
Patent No~ 3,574,459 to Hartwig an~ Schnell, in which a single
optical axis is rotated 180 between successive scans by a
^`~ prism~
:' :
' ; ' ''
~. .
, :
~ ~ - 2 - ~
., .
.'.', ' ~.
3~a~6
SIIMM~RY OF THE INVENTION
_
In accordance with one aspect o~ this invention there
is provided an optical scanning system for projecting an
image of an object from an object plane to an image plane
and having first and second optical.axes extending be~ween
said object plane and said image plane, s;aid image being in
a fir~t orientation at said image plane when projected along
said first optical axis and in a second orientation, rotated
180 about the axis of propa~ation from saia first orientation,
when projected along said second optical axis, said system
including: . ~
a lens to project an image from said object plane
.
.
to said image plane,
a photoreceptor disposed for uni-directional motion
~ .. . .
at said image plane,
. drive means for.effecting relative reciprocatory :-
1 scanning motion of said object and said optical axis, ..
J . optical axis arive means to place said object plane
.' and saia image plane in optical communica~ion successi~ely
20 along said first and said secona optical axis, and to swi~ch
between one to the othar of said optical axes at the end of
said reciprocatoxy motion in each airection, . -
whereby said optical scanning system is effective to
pxoject an image ~f said object onto said moving photoreceptor .~.
~i . . during both directions o~ reciprocatory scannin~ motion.
~ ~ .
'I
`I , . .
*
3 ~
i
:
, .
~'`
~Q5~6
For a better understanding of this invention,
reerence is made to the following detailed description given
in connection with the accompanying drawings.
DRAWINGS
Figure 1 is a plan view of an optical system accord-
ing to the present in~ention and illustrat:ing an image orienta-
tion in one direction of object scan.
Figure lA is a partial view o the system of Flgure
1 lllustrating an image orientatiQn in the reverse object scan
direction.
Figure 2 is a front view taken along the line II-II
of Figure 1.
, Figure 3 is a front view taken along the line III-III
of Figure 1.
Figure 4 is a view from the left side taken along the
line IV-IV of Figure 1.
. ~ .
i~ , '
1:
:1 .
`' , : .
:, :
`1 :
, . . .
~: : . ' ' '
,.,;, ~ , ~ . :
3~
,;,; - ::,
~ -3a~
'1 , "" . ' . ;
: ,~
~L~5399~6
Figure 5 is a view from the left side taken along
the line V-V of Figure 1
DESCRIPTION
Referring now to Figures 1 and 2, the optical
scanning system of this invention is generally indicated at 2
and extends between an object plane or surface 4 and an lmage
plane or surface 6. The optical axis 8 of the system, includes
parallel or alternate optical paths 8A and 8B and extends from
object plane 4 to image plane 6.
Figure 2 is a front elevation view of the first
optical axis 8A and along with Figure 1, shows a first
reflector 12 and a second reflector 14, both of which fold : :
the optical axis 8, and a projection lens 10 all disposed in
optical al.ignment along the fir~t optical axis 8A between the
object plane 4 and the image plane 6. An object 0 on the
object plane 4 is imaged at I by means o~ the pro~ection lens 10
on the image plane 6. The object 0 is represenked in Figure 1 .
by the chara~ters FR placed face down on khe object plane 4. .:~:~
,
These character~ project along the first optical axis 8A and
.)20 . onto the image plane 60 The image characters FR projected ..
along optical axis 8A in Figure 1 are rotated 180 relative
to the orientation of the object characters FR.
In a typical photocopying apparatus, the image is
pro~ectea onto a photoreceptor, located at the image plane 67
and mo~ing in a continual uni-directional movement as indicated :
:~ - by the arrow 7~
'I In a scanning mode o~ operation, the object o is
~:i : reciprocated on the object plane 4, relative to the optical
axis 8A along a path of travel ind.icated by the arrow 5.
During this scanning, only a narrow band o the object is
... .
:. .
~ . -4-
' :
:
... . ..
1053g~6
exposed at any time This continual and progressive exposure
results in a composite image of the scanned object. When
the object o is moving in the scan direction 5A, its image
is projected along first optical axis 8A and laid down on
the moving photoreceptor as shown in Figure 1. ~ow if the
system geometry were maintained in the r~eturn direction of
scan 5B, the image projected along optlcal axis 8A onto the : ~
image plane would be a wrong reading image. It is for this ~.
reason that the prior art typically does not expose the object ..
on the return motion, but instead uses quick return devices to ~ ~ :
minimize the time lost during the return motion.
Second optical axis 8B lS provided for use during
the reverse scanning motion in the direction 5B and is shown ~.
in plan view in Figure 1 and in various elevations in Figures ..
. .
3, 4, and 5O Optical axis 8B includes, in optical alignment
I between the object plane 4 and the image plane 6, the first
reflector 12, a third reflector 16, a proiection lens 20,
a fourth reflector.l8, and the second reflector 14. All of
. the mirrors 12, 14, 16, and 18 are shown as oriented at 45
relative to.the optical axis so as to fold the same by 90,
:.;- These angles are.convenient for illustration of the present
, invention, but the concept of this invention is not limited . - ... . . .
to such geometry.
First~reflector 12 and second reflector 14 are mounted
for~rotation on axes coincident with the optical.axis 8. In
the geometry illustrated, reflectors 12 and 14 are rotatable
in:90 arcs :about~these axes 80 between ~uccessive reciprocal
s~an movements O ~ In Figure 2, the reflectors 12 and 14 are in
pOSitiQn 90 that ob~ect plane 4 and lmage plane 6~are in
30 ~ ~ optical communication along the first optical axis 8A.
, ~ . .
~ 5-
:,
: :i
~(9S3~
In Figures 3, 4, 5, reflectors 12 and l4 have been shifted
90 so ~hat object plane 4 and image plane 6 are in op-tical
communication along the second optical axis 8B. When the object
o is imaged at I by means of the projectLon lens 20 along optical
axis 8B, the characters FR are rotated 180 (-Figure lA) relative
to their orientation when projected along optical axis 8A
(Figure 1~. During scanning, when the object o with its
characters FR is moving in the scan direction 5B, its image is
propagated along the second optical axis 8B, and laid down on
the moving photoreceptor as shown in Figure lA~ As viewed
from the opposite side of the paper looking up at Figure 1,
it wil~ be appreciated that the object is, of course, right-
reading, the only difference being that these successive
images are rotated 180 relative to each other.
To summarize, when the object with ltS charaters
FR is moved in the scan direction 5A its image is projected
along optical axis 8A onto the image plane at I as shown in
... ..
Figure lo When the object characters FR are moved in the
.
scan direction 5B, the image is projected along optical
~! ) axis 8B onto the image plane at I as shown in Figure lA.
The rotatable reflectors 12 and 14 are operatively
connected to the document reciprocal drive, as represented
in he drawings by the ~otted lines. The details of the
.
reciprocating ~ri~e and of the re~lector drive are not necessary
~o an understanding o~ the present invention. Indeed, such
mechanism may take ~e~eral forms. The essential thing is
~ that the reflectors 12 and 14 are in synchronism with the
;`'!: reciprocating motion of the object O. Thus, when the object O
is moving in scan direction 5~, reflectors 12 and :L4 are in
.' ~ ' ' .
~ 30 position to project an image along optical axis 8A. At the
.. . .
, ~
., : :
:~ .
:,, , ' ~''
; ~ .
. . . . . .. . . . ...
~L~53~6
end of the stroke in direction 5A, and be~ore the return
stroke in direction 5B, reflectors 12 and 14 are shifted so
as to project along optical axis 8B.
It will be appreciated that the invention described
herein provides a strip scanning optical system capable of
projecting images during both directions of reciprocal scan
movement~ This has been done by optically rotating the
optical axis or in effect, optically reversing the photo-
receptor between successive scans. By projecting useful images
in both directions o~ scan movement, clearly the ratio of
useful time to lost time in the operation of a photocopy.ing
.) machine employing this invention is greatly increased.
~he description given above has been with xeerence
to a system in which the optics are stationary and the object ..
is reciprocated... While this is presently preferred, it will
be appreciated that the concept of the invention is not limited ~ .:
to such an arrangement~ It is, of course, possible to have
. the object remain stationary and have the optical system
reciprocate relative to it.
Reduced to its basics, the invention involves
rotating a plane 180 about each of the coordinate axes lying
. in the plane. The effect of this is to rotate the plane 180
about th~ thira coorainate axis, the axis normal to the plane. : -
. : .
. . In terms of an image projection system as is invo~ved
here, the propa~ating image wavefront is taken as a plane for
~. the purpose of a rame of reference in describing and defining ~:
; ~ the geometry. The axis of propagation of the image is the ~.
: ~ axis normal to the plane and is the axis about which it is .
,; ~ ..
~ desired to rotate the image by 180. In view of the foregoing, : .
-
...
.j 7
.1 . :
. . .
.. . ~'; ,
~, , .
~53~
it will be clear that such concepts in the claims as imagewavefront, planar wavefront, and coordinate axes lying in the
wavefront, are not limited to an actual plane wavefront en-
vironment. The planar wavefront image propagation is simply
a useful aid to understanding the invention~
. The foregoing description of an embodiment of this
invention is given by way of illustration and not of limitation.
The concept and scope of the inven~ion are limited only by the
following claims and equivalents thereof which may occur to
others skilled in the art.
') ~
'.
~,
, I
.1 .
i:
~,
. I .
,L . ~ . ~ .
`; ' ~ .
~ ' . . .
' `I . ' " '~ ' '
i .
'', ', . ~ '
'; .
` ~ -8-
,
.~, . . .
' ' ,: :
, . , . ~.
