Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~(:973715
This invention relates to an optical system for
multiple imaging of a linear object whereby a linear object is
imaged to yrovide a number of sections arranged side-by-side.
In imaging systems in which an image is to be
scanned electronically, such as in facsimile readers for
electronic transmission of printed matter, the object, usually
a line across a page of print, is imaged on to a solid state
detector device, such as a charge-coupled device (CCD) array.
The difficulty and cost of making a solid state,
10 or other type, o~ imager usually increases with size. In
scanning or making apparatus, imaging a thin linear section of
a page~ it is a practice to image on an axray having 1728
elements, for an 8 1/2" wide page and with 200 lines per inch
resolution. The length of such an array is close to one inch
and the width about one hundredth of an inch. Such dimensions
result in expensive manufactures. If the imager is of silicon,
for example, the material uniformity, distribution of defects,
processing and reliability in general place severe limits on the
f fabrication yield of imager chips which are long and thin. An
20 improvement in fabrication yield would be possible if the imager
chips need not be as long as one inch, and also if they are f;
increased in width. This would reduce cost and improve handling
ability.
The present invention provides an optical system
which provides for an imager array which has less disparity ~ `
between width and length than would occur if a linear object is
imaged as a continuous line. Multiple images are produced and
rearranged such that the images are in side-by-side and over-
lapping relationship, with different segments of the object
30 in adjacent proximity. An imager can detect and reconstruct an
entire image of the object from the different imaged segments.
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This is obtained by a serles of mirrors situated side~by-side,
inclined and rotated relative -to each other.
The invention will be readily understood by the
following description of an embodiment, by way of example, in
conjunction with the accompanying drawings, in which:-
Figure l diagrammatically illustrates thepositional relationship between an object, a mirror, an image
reflected by the mirror and the vertical image of the object
as apparently seen by an observer;
Figure 2 illustrates diagrammatically the
B positioning of ~u~ images, with an inclined mirror and a
non-inclined mirror;
Figure 3 illustrates diagrammatically a three
mirror arrangement for producing three imagas (and three virtual
images);
Figure 4 illustrates diagrammatically how the
positioning of the three virtual images produced by a three mirror
system of Figure 3 is used to position a lens and associated
imaging device;
Figure 5 illustrates diagrammatically the system
of Figure 4, with the mirrors also rotated relative to each other !~
as well as inclined relative to each other.
As illustrated in Figure 1, if an object 10 is
placed in front of a mirror ll, an observer at 12, will see an
image of the object 10 which is apparently bahind the mirror -
at 13. The image 13 i5 called the virtual image. The rays 14
and 15 from the top of the object lO, after reflection, appear
to come from the top of the virtual image 13, as indicated by
the dotted lines 14a and 15a. This diagrammatic arrangement
can be used to design other imaging systems.
Consideriny Figure 2, this illustrates how
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virtual images can be displaced. In this figure ray 20 from the
top of object 10 is reflected by the mirror 11~ To an observer
of this ray at position 21 the top of the object 10 will appear
to be at 22 of the virtual image 13. If the mirror is inclined
to lla, at an angle ~ relative to the original position at 11,
then the ray 20 from the top of the object 10 will he reflected
and observed by an observer at 21a and the top of the object 10
will appear to be at 22a of the virtual image 13a. The virtual
image 13a has a different orientation with respect to virtual
image 13. However the lower portion of virtual image 13 is
adjacent to an intermediate portion of virtual image 13a. Thus
two portions of an object are now in juxtaposition. It is
possible to increase the number of portions of the object in
such juxtaposition by having a series of mirrors inclined with
respect to each other.
Considering Figures 3 and 4, rays 25, 26 and 27 are -
rays from different parts of object 10. Three mirrors 11, lla
and llb are provided, mirror lla inclined relative to mirror 11 ;
and mirror llb inclined slightly farther, relative to mirrors 11
` 20 and lla~. With both mirrors lla and llb, the front planes, that
is the reflective planes, are coincident on the same axis on the ,
plane of mirror 11, as indicated by -the line 28. Figure 3
shows the mirrors to a much larger scale than in Figure 4, to
illustrate the relative angular inclination of the mirrors.
The rays 25, 26 and 27 are reflected ~rom the
mirrors. The virtual images formed are seen in Figure 4 at
13, 13a and 13b. It will be seen that the virtual images overlap ~-~
~` with different portions or segments of the object in juxtoposition -
they will in fa-ct be substantially imposed on one another in
Figure 4. Each mirror 11, lla and llb is small, needing to be
only wide enough to reflect or "image" only that part of the
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object which corresponds to the po~tion overlapping at the virtual
images. Thus each mirror th~n reflects only the associated part
of khe object. A lens system 29 receives these reflections and
focusses them on to a detector device 30. Again, at this time,
the image portions are substantially superimposed.
Figure 5 illustrates the final feature which will
provide a rearranged image suitable for scanning or reading.
In Figure 5 the x-y plane corresponds to the plane of the drawing
of Figure ~. As shown, the mirrors 11, lla and llb are inclined
relative to each other, as in Figure 4, but the mirrors are now
also rotated relative to each other, as indicated by angles 31
and 32. This rotation separates the three parts of the images.
The object 10, as an example a line of print on page 33, is
shown divided into three sections numbered 1, 2 and 3. The
corresponding sections are shown on an imager 34. It will be
appreciated that, owing to the small width of each mirror, rays
from only a section or portion of the object 10 are reflected to
the lens by each mirror and due to the relative inclination it
is rays from a different section of portion that are reflected ~ `~
by each mirror. Depending upon the number of sections or
portions it is desired to divide an object into, so the number
of mirrors, and their width, is selected. Each mirror is
normally inclined and rotated progressively relative to a
previous mirror, although by varying this arrangement, the
various images of the sections or portions of the object can be
arranged in differing relationships.
As an example of one form of optical system as
illustrated in Figure 5, object 10 is assumed to be a printed
line 127 mm wide and 215 mm lony on a page, as represented by
33. The lens system 29 is assumed to have a focal length of
75 mm. The detector on the images 34 is composed of three ~;~
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576 - element photosensor arrays. The inter element spaciny is
13 microns giving the array a total length of 7.49 mm. The
arrays are separated by 50 microns. 200 lines per inch
resolution requires the object distance represente~ by, for
example, the length of the light ray 35 from page 33 to the lens
system 29, to be 792.5 mm. To enable construction of the system
illustrated in Figure 5, page 33 is 750 mm from mirror lla and
lens system 29 is 42.5 mm from the mirror lla. Angle 31 is
calculated to be 0.067 and angle 32 is 0.13. The relative
inclination of the mirrors, particularly as illustrated in
Figure 4, is such that mirror lla is inclined at 2.5 with
respect to mirror 11 and mirror llb is inclined at 5 relative to
mirror 11. ~s seen in Figure 4, the virtual objects 13, 13a
and 13b have segments, the particular segments of interest, which
lie at slightly different distances from the lens system 29.
The final imager focussed by the lens system will also be
located at slightly different distances. It has been found, in
a system as detailed above, that the maximum depth separation
between these image segments is 0.07 mm. By stopping the lens
2~ system 29 to a f number of 8 there is sufficient focal depth to
give clear details on all three segments on the detector.
Thus, with the present in~ention, the angular
field of row of the imaging system is narrowed and the size of
the photosensor arrays can be reduced. Both of these yield
substantial cost savings.
The arrang~ment as illustrated in Figure 5 is a
particular example of the basic idea. In Figures 2 to 5 there
can be more than one pivot axis 28 tFigure 3). The location
of pivot axes, size of mirror planes, the o~iect distance
exemplified by the separation between object 10 and mirror 13
in Figure 2, the inclination of the mirrors and the angles (31
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and 32 of Figure 5) can be arbirtary and would be optimized ~or
particular applications and for different detector array
geometries.
Also, although more convenient from imaging
considerations it is not essential that mirror 11 be parallel
to the plane of the object, (that is normal to ~he axis of the
light path from the object), with th~ mirrors lla and llb
sequentially tilted. For example mirror llb could be normal
with mirrors 11 and llc diff~rentially tilted. This would
result in the different portions of the object not being in a
direct sequence and would require modification to the scanning
system.
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