Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an optical system
for imaging an elongate object in rearranged sections, and
particularly relates to the imaging of a line across a page
by rearranging the image into a plurality of sections in a
stacked or side-by-side arrangement.
The difficulty and cost of making a solid state
or any other type of imager usually increase with the size,
either the length or the area, of the imager. If the spatial
extention of the image and hence the imager length can be
reduced, advantages can be gained in the materials reliability
and manufacture of the imager.
Imagers are frequently used in scanning or
reading apparatus such as copiers and facsimile machines.
In those applications it is sometimes necessary to image a
thin linear section of the page, either along the width or the
length, onto an imager array. For example, a thin section
across the 8~" width of an ordinary page is imaged onto a
solid state imager array having 1728 elements. The lengths
of the imager arrays are close to one inch and their widths
about one hundreth of an inch. If the imager is made of
silicon for instance, the material uniformity, distribution
of defects, processing and reliability in general place severe
limits on the fabrication yield of imager chips that are
long and thin. An improvement in fabrication yield would be
-possible if the imager chips need not be as long as one inch.
The present invention can be used to design an
imager array having less disparity between the width and the
length in the detector area. At the same time, such an imager
would retain all functions of a longer imager array.
The invention uses prisms, or other light
"bending" devices, to deflect the light rays and to cause lateral
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displacement of sections of a linear object. The number of
prisms and/or other devices used can vary according to the
number of sections the object is to be divided into, and the
particular relative displacement and final image form.
The invention will be readily understood by the
following description of various embodiments, by way of example,
in conjunction with the accompanying diagrammatic drawings,
in which:-
Figure 1 is a p~an view of two prisms producing
a set of imagers inverted and laterally displaced with respectto each other;
Figure 2 illustrates displacement of an image
by a glass plate;
Figure 3 is a perspective view of a system
combining the features of Figures 1 and 2 to give inversion,
lateral displacement and height displacement of an image;
Figure 4 illustrates the use of prisms to give
displac~ment;
Figure 5 illustrates a modification of Figure 4;
Figure 6 is a perspective view of a system for
obtaining quadruple folding of an image;
Figure 7 diagrammatically illustrates the
related positions of the various sections of a linear object
as produced by the system of Figure 6.
- In Figure 1 are illustrated two prisms 10 and 11,
their base surfaces forming a common interface 12. Prism 10
has sides 13 and 14 at right angles to each other and at 45
to the interface 12, and prism 11 has sides 15 and 16 at right
angles to each other and at 45 to the interface 12. The
prisms can be cemented together or merely in contact at the
interface. One of the prism base surfaces at the interface
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is half-silvered, or coated with a 50% reflection coating.
The object 17 is represented by the two arrows 17a and 17b.
Rays 20 and 21 from 17a pass through the prisms
10 and 11 with a displacement in the same direction as that
indicated by the object arrow 17a. The image of 17a appears
as 22a. The rays 23 and 24 from 17b are partially reflected
at the interface 12 when passing through prism 11. The image -
of 17b is inverted and appears as 22b. In practice a lens,
indicated in dotted outline at 25, can be used to collect all
the rays from the object 17, not only the parallel rays shown.
The focussed images can be read at an imager.
In the arrangement of Figure 1, if the object
17 is aligned on a line perpendicular to the plane o~ the
interface 12 and equally spaced about the interface, images
22a and 22b will be superimposed. Actually, the combination
of prisms and interface, as illustrated in Figure 1, will
produce double images as a viewer at the imager position can
observe objects through faces 13 and 15 simultaneously.
Therefore, a further image, composed of two superimposed
images of 17a and 17b will be produced, displaced from that
illustrated in Figure 1 at 22a and 22b. In this second image,
, indicated in dotted outline at 26a and 26b, the image is
reversed compared to 22a and 22b.
An image can be displaced laterally, in a
- direction normal to the longitudinal axis of the object, by a
~ parallel sided glass plate, as illustrated in Figure 2. Glass
-f plate 30 is inclined relative to the object 17a and the lateral
;~ displacement of the image 22 is related to the inclination of
the plate relative to the plane of the object 17.
The lateral displacement obtained by a glass
plate can be combined with the subdivision obtained by two
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prisms to give both division and separation. This is
illustrated in Figure 3. For clarity, only a ray representing
the centre of each section 17a and 17b of the object 17 is
illustrated, at 35 and 36 respectively. It will be seen that
instead of the images of the two object sections being super-
imposed, one section, 22b, is displaced laterally relative to
the other, 22a. This is obtained by the displacement of the
rays from object section 17b prior to entering the prism 11,
by the glass plate 30. Two sets of images are again formed,
as described with respect to Figure 1, and the second set of
images are indicated at 26a and 26b.
For use as a reader, or scanner, either set of
images, 22a and 22b or 26a and 26b, can be used. The detector,
or imager, length is halved in the example of Figure 3 as only
the overlapping section of the images are used. By repeating the
prism arrangement, it is possible to further subdivide, giving
a length one quarter of what would otherwise be required.
Displacement of an image can also be obtained
by tilting the prisms, as illustrated in Figure 4. The image
22 is displaced, the displacement of image 22 in Figure 4,
relative to the object 17, is shown related to a normal
undisplaced position which would occur at the image plane at the -
end of dotted line 40.
By tilting and rotation of the prisms, both
- division and displacement can be obtained. This is illustrated
in Figure 5. Prism 10 is rotated relative to prism 11, on the
interface 12. The images are overlapped and also displaced,
in the same manner as in Figure 3. Two sets of images are
again produced, 22a and 22b, and 26a and 26b. Repetition of
the prism arrangement of Figure 5 will also give further
overlapping of the images.
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The above arrangements for subdlvision of a
linear object into separate sections, and displacement of
these sections, t~ provide what can be termed an "area image"
rather than a linear image, is illustrated in relation to a
line scanning device in Figure 6. Two sets of prisms are
provided, 10 and 11 and 45 and 46, to give quadruple folding.
The prisms 10 and 11 separate the image sections by a larger
amount than prisms 45 and 46. A lens 47 is used to focus the
images on a detector 48. A sheet of paper, or other planar
member, is indicated at 49 with a linear object, such as
a line of print, indicated at 50. The line 50 is shown divided
into four sections 50a, 50b, 50c and 50d. One set of images is
shown on the detector 48, at 51a, 51b, 51c and 51d. While
image sections 51a and 51b, representing object sections 50a
and 50b respectively, are sequential, image sections 51c and
51d, representing object sections 50c and 50d respectively, are
transposed, with 51d between 51b and 51c.
It should be appreciated that actually four
complete images are formed, each image a complete reproduction
of the entire object. However, the images are displaced, in
the direction of the longitudinal axis of the object, but
' overlapping in such a way, that a section extending across all
the images will contain a different part of the object, thus
giving the effect of a divided, or sectioned image. The
-actual extent of all the images is indicated, by way of example
only, by dotted lines 52 in Figure 6.
The amount of rotation, and the sense of
rotation, of one prism relative to another in a pair of prisms,
will determine the image arrangement provided.
Figure 7 illustrates, very diagrammatically,
the detailed line rearrangement of a system as in Figur~ 6.
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In Figure 7, the prisms are shown in outline and their tilt
and relative rotation are not indicated, this being
illustrated in Figure 6. A line 55, representative of a linear
object such as a line of printing, is indicated, divided
into eight sections, the ends of the section numbered 1 to 9.
One set of images only is shown, and only the overlapping
sections of this set. Thus, after the rays from line 55 have
passed through the prisms 10 and 11, a first image 56 could
be observed by an observer at this position. The image would
be as indicated at 57. After the rays have passed through the
further prisms 45 and 46, a second image could be observed at
58 by an observer at this position. The image would have the
form as indicated at 59, bearing in mind that four complete
images are actually formed staggered laterally, with one section
in each image overlapping - as indicated in Figure 6. The
numbers at the section ends of the line 55 are shown as they
would be, that is reversed where this is so. It will be
appreciated that a second set of images could be observed if
an ob~erver was looking at the right hand side of Figure 7,
instead of the left hand side, ie., as indicated at 60. The
image at 60 has been displaced slightly in Figure 7, for
clarity, but would be in alignment with 58.
In practice, one of the images produced in the
various arrangements would be imaged on some form of detector,
for example a charge coupled device (CCD) array. By suitable
electronic control, the image would be scanned so that the
sections of the image would be read in the correct sequence.
Alternatively, additional optical devices could be used to
provide sequential imaging, and even to overcome the reversal
of some sections, but it should be noted that some loss of
power could occur if additional optical devices were incorporated.
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While the prisms 10 and 11 and 45 and 46 have
been shown as right-angle prisms, with the other angles at 45,
these angles can vary. However, selection of the angle is
desirably such as will reduce a stygmatism, and 45 for the
base angle is a good compromise.
The positioning of the prisms relative to the
object~ is not critical but rotation of the prisms relative
to each other, and alignment of the prisms relative to each
other, is more critical. As described, rotation of the prisms
is not essential as glass slices can be used to provide
displacement.
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