Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to direct imaging
i apparatus for electronic transmitter for documents and the like,
such as for facsimile transmitting systems.
- In conventional imaging apparatus, an imaging of
the object, usually a line across a page, is obtained by a
lens system. Such a system is large, it being necessary to
provide the necessary light path length for the lens system.
The object - the document being copied is some distance from
the imaging device.
The present invention provides for positioning
the imaging device - the detector array - in close proximity
to the document. This requires a completely different arrange-
ment for illuminating the document. For a transparency it
; would be satisfactory to illuminate the document from the
back, that is from the side remote from the detector or
imaging device. However, for normal paper documents, the
paper is so opaque that the transmitted light level is too low
to give an acceptable signal from the detector. Also such a
way of lighting would prevent, or at least make very difficult,
~u copying a page of a book or similar document, particularly if
printed on both sidesO
With the present invention, light is passed
through the detector array onto the document, the light then
reflected from white, or light coloured, areas on to the
,~ detectors of the array. To prevent saturation of the detectors,
opaque areas are provided beneath detector elements, with gaps
between elements and associated opaque areas for light to pass
through to the document.
The invention will be readily understood by the
following description, in conjunction with the accompanying
drawings, in which:-
,,,4;` Figure 1 is a diagrammatic illustration of a
conventional form of apparatus;
Figure 2 is a diagrammatic illustration of aform of apparatus in accordance with the present invention,
- in perspective;
Figure 3 is a diagrammatic cross-section through
one form of apparatus in accordance with the present invention;
Figure 4 is a diagrammatic cross-section,
:-
similar to that of Figure 3, illustrating the relevant
dimensions;
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Figure 5 is a plan view of part of an imaging
apparatus, as in Figures 3 and 4.
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Figure 1 illustrates the basic arrangement ofmany conventional forms of images, or scanners. The document
is indicated at 10, the arrow 11 indicating an object on the
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`~` document, for example the line of print. The document is
illuminated by a light source 12 and light reflected from the
object is focussed by a lens system 13 onto an imager 14.
,:
One form of imager is a charge-coupled device (CCD) array. The
~0 arrangement of Figure 1 is quite bulky as the light path
` between object 11 and the imager 14 has a certain minimum to
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enable an acceptable lens system to be used.
Figure 2 illustrates the basic arrangement of the
present invention. The document 10, indicated in chain dotted
outline, is positioned on a detector head 20 which is composed
of a transparent substrate 21 on which are formed the detector
elements 22. Electrical connections to the detector elements
are indicated at 23. Over the substrate 21 and elements 22 is
placed a transparent spacer 24. A source of illumination is
indicated at 25. The object is indicated by the arrow 11, as
in Figure 1.
-- 2
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The apparatus of Fiyure 2 is seen in cross-
section in Figure 3, and in more detail in cross-section in
Figure 4. To prevent saturation of the detector elements 22
by the direct light from light source 25, through the substrate
21, opaque material 26 is positioned beneath the elements 22.
In the example illustrated in Figures 3 and 4 the
`~ elements 22 are annular and apertures or gaps 31 are formed in
the opaque material 26 coincident with the central aperture 30
; in each element 22.
;,; 10 The relevant geometry of the appararus is
illustrated in Figure 4. The substrate thickness is Ts; the
separation distance between document 10 and the photoconductor
elements 22, which is substantially the same as the thic]~ness
of the transparent spacer 24, is TF; the centre spacing between
detector elements is C; the detector diameter is D; and the
light aperture is A. For simplicity it is assumed that the
lamp is an isotropic source and the document is an isotropic
reflector. The angle of total internal reflection is ~ and is
'~ near 40 for glass. No light falls on the document for r - the
sideways displacement from the aperture centre - greater than
A/2 + .84 TF; (.84=tan 40). Illumination within this area is
substantially constant. Because the entrance angle within the
glass is 40 maximum, light cannot spill from the endmost
illuminated point beyond a distance A/2 + (.84 TF) X 2 in the
... .
'~ detecting plane. If a resolution of 200 lines per inch is
; required, [A~2 + (.84 TF) x 2] ' .005", that is
A + 3.36 TF ~ .005. If TF < .001,
i A ' .001.64.
In practice the dimensions for A and TF could
be slightly larger as the light intensity near the edges and at
. high angles is over estimated in the approximation. In practice
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A and TF would be optimized to take problems of manufacture and
sensitivity into account. Various light ray paths are indicated
by lines 35 in Figure 4. If, as is likely, the opacity of the
opaque material varies with thickness, a certain amount of
light will pass through the corners of the opaque material, as
indicated at 36.
In Figures 3 and 4, the opaque material 26
is shown as being in the transparent substrate. This can be
done, for example, by photolithographically etching the
substrate and then depositing suitable opaque material in the
etched holes. The elements 22 can be formed by conventional
; thin film techniques. Alternatively, it would be possible to
deposit the opaque material on top of the substrate, either
through a mask or by forming a continuous strip and then
photolithographically etching to form the desired pattern. The
elements 22 would then be formed on top of the opaque material.
` The transparent spacer 24 can be formed by depositing a suitable
material over the elements 22, for example a silica glass. A
;~ cover is indicated at 400
; 20 Figure 5 illustrates one arrangement of electrical
connections to the detector elements 22. Conductors 36 extend
from one side of the elements and conductors 37 extend from the
other side. The conductors 36 and 37, in the example
illustrated, are formed on the substrate 21, extending over the
opaque material 26. The inner ends 38 of the conductors extend
,.,
under the elements and are in electrical contact therewith.
The conductors 36 and 37 can be connected in
a matrix formation to provide for selective connection of the
elements to a detector circuit.
` 30 In Figures 4 and 5, the detector elements 22
; are annular, being of circular form with circular apertures 30
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in the detectors and similar apertures 31 in the opaque
; material 27. An alternative is for the detectors to be
rectangular, for example square, as indicated by dotted lines
22a in Figure 5, with rectangular, that is square, apertures -
as indicated by dotted lines 30a - in the detectors with similar
apertures in the opaque material.
`- The particular form of light, that is wavelength
;~ (or mixtures of wavelengths) may vary, the light being such as
-~ will be reflected efficiently by the document. The substrate
will be transparent to such light and the opaque material opaque
; to such light.
The detector elements 22 can be spaced close
enough together to provide the desired resolution, or spaced
a predetermined number of units apart with lateral stepping of
the head. In another arrangement, a plurality of lines of
~ detector elements can be provided, the detectors in a staggered
- relationship, to give close overall spacing of detector elements.
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