Note: Descriptions are shown in the official language in which they were submitted.
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B~CKGROUND OF THE INVENTION
The present invention relates to improvements
in the field of monochromic and polychromic dynamic
printing. More particularly, the invention is concerned
with an improved method and apparatus for reproducing
an image by electro-coagulation of an electrolytically
coagulable colloid and transferring the image thus
reproduced onto an end-use support, such as paper.
Applicant has already described in his U.S.
Patent No. 3,892,645 of July 1, 1975 an electrocoagulation
printing method and system in which a thin layer of a
liquid composition containing a colloid such as gelatin
or albumin, water and an electrolyte is interposed
between at least one pair of opposite negative and
positive electrodes spaced from one another to define
a gap which is filled by the liquid composition. In
one embodiment, there is a plurality of electrically-
insulated juxtaposed negative electrodes and selected
ones thereof are electrically energized to pass electric
pulses through the layer at selected points to cause
point-by-point selective coagulation and adherence of
the colloid in variable thickness on the positive
electrode directly opposite each energized negative
electrode, thereby forming imprints.
It is very important that the gap between the
negative and positive electrodes be uniform throughout
the active surfaces of the electrodes since otherwise
there will be a variation in the thickness of the layer
and thus a corresponding variation of the electrical
resistance thereof at different locations between the
electrodes, which will result in a non-uniform image
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reproduction as the thickness of the coagulated colloid
is propor-tional to the amount of current passed through
the layer. As this gap is o~ the order of 50 ~u, its
uniformity is of course very difficult to control. This
is especially true in the c~se ~here the positive
electrode is in the form of a revolvin~ cylinder so that
it may also be used as a printing roller for high speed
transfer of the image reproduced onto paper or the like;
such a cylinder must be of high precision and have a
cylindrical surface virtually free of any defects, and
is thus very costly. Moreover, since the negative
electrodes are generally energized more than once in
the reproduction of an image, these become polarized
resulting in a gas generation and accumulation at the
negative electrodes, which adversely affect the image
reproduction.
SUMMARY OF THE INVENTION
It is therefore an object of the present
invention to overcome the aforementioned drawbacXs and
to provide a method and apparatus for reproducing an
image by electro-coagulation of a colloid and transfer-
ring the image thus reproduced onto an end-use support
at high speed, which method and apparatus do not -
necessitate the use of high precision cylinders for
coagulating the colloid and in which the electrode gap
uniformity can be easily controlled.
It is ano'her object of the invention to
provide a method and apparatus of the above type, in
which the image reproduction is not adversely affected
by electrode polarizàtion.
According to one aspect of the present inven-
tion, there is provided amethod of reproducing an image
and -transferring same onto an end-use support, which
comprises the steps of:
a) providing a positive electrolytically
inert electrode in the form of an endless elongated
belt moving at substantially constant speed along a
closed horizontal path and having an electrode active
surface extending vertically, and a plurality of negative
electrolytically inert electrodes electrically insulated
from one another and arranged side-by-side in recti-
linear alignment to define a series of corresponding
electrode active surfaces disposed transversely of
the belt and spaced from the positive electrode active
surface thereof by a constant predetermined electrode
gap;
b) filling the electrode gap with a sub-
stantially liquid colloidal dispersion containing an
electrolytically coagulable colloid, a liquid dispersing
medium and a soluble electrolyte and having a sub-
stantially constant temperature'
c) electrically energizing selected ones of
the negative electrodes to cause point-by-point
selective coagulation and adherence of the colloid onto
the positive electrode active surface of the belt
opposite the electrode active surfaces of the energized
negative electrodes while the belt is moving, thereby
forming a series of corresponding dots of coagulated
colloid representative of a desired image,
d) removing any remaining non-coagulated
colloid from the positive electrode active surface,
e) treating with a coloring agent the
colloid either before or after the coagulation thereof
in step (c) to obtain dots of colored, coagulated
colloid; and
f) contacting the clots of colored, coagulated
colloid with an end-use support to cause transfer of
the coloring agent onto the end-use support and thereby
imprint the end-use support with the image.
The present invention also provides, in a
further aspect thereof, an apparatus for carrying out
a method as defined above. The apparatus of the invention
comprises a positive electrolytically inert electrode
in the form of an endless elongated belt having an
electrode active surface extending vertically, means
for moving the endless elongated belt at substantially
constant speed along a closed-horizontal path, and a
plurality of negative electrolytically inert electrodes
electrically insulated from one another and arranged
side-by-side in rectilinear alignment to define a series
of corresponding electrode active surfaces disposed
transversely of the belt and spaced from the positive
electrode active surface thereof by a constant pre-
determined electrode gap. Means are provided for
filling the electrode gap with a substantially liquid
colloidal dispersion containing an electrolytically
coagulable colloid, a liquid dispersing medium and
a soluble electrolyte and having a substantially
constant temperature, as well as means for electrically
energizing selected ones of the negative electrodes to
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cause point-by-point selective coagulation and
adherence of the colloid onto the positive electrode
active surface of the belt opposite the electrode active
surfaces of the energized negative electrodes while the
belt is moving, thereby forming a series of correspond-
ing dots of coagulated colloid representative of a
desired image. The apparatus ~urther includes means
for removing any remaining non-coagulated colloid from
the positive electrode active surface, means for treating
with a coloring agent the colloid either before or after
the coagulation thereof to obtain dots of colored,
coagulated colloid, and means for bringing an end-use
support into contact with the dots of colored,
coagulated colloid to cause trans~er of the coloring
agent onto the end-use support and thereby imprint the
end-use support with the image.
Thus, according to the invention, by using a
positive electrode in the form of a moving endless belt
onto which the colloid can be coagulated, high speed
image reproduction and transfer can be achieved at
substantially reduced cost as compared to using a
revolving cylinder of high precision. The use of such
an endless belt has also the advantage of enabling one
to more easily control the uniformity of the electrode
gap.
In a preferred embodiment of the invention,
the endless elongated belt comprises a vertically
disposed sheet material having at least a surface layer
made of an electrolytically inert metal and defining the
aforesaid positive electrode active surface. The sheet
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material is driven along the closed horizon-tal path by
a drive roller located opposite the negatiVe electrodes
with -the sheet material therebetween, the drive roller
haviny a center axis extending substantially in align-
ment with the negative electrodes. This arrangementenables the colloidal dispersion to be continuously
injected under pressure on the sheet material adjacent
the electrode gap so as to press the sheet material
against the drive roller and thereby maintain the
aforesaid constant electrode gap. On the other hand,
since the electrode gap is continuously supplied with
fresh colloidal dispersion, gas bubbles generated as a
result of electrode polarization are continuously
removed by being entrained with the excess colloidal
dispersion which is allowed to drain by gravity. In
this manner, any gas accumulation that may hinder the
image reproduction is prevented.
The surface layer of the sheet material which
defines the positive electrode active surface must be
made of a metal that will resist electrolytic attack
and enhance electro-coagulation, such as stainless
steel, platinum, chromium, nickel, aluminum or tin.
The sheet material is preferably made entirely of such
an electrolytically inert metal, but it can also be
made of synthetic plastic material having a surface
coating of electrolytically inert metal, it generally
has a thickness of about 0.004 to about 0.010 inch.
The negative electrodes are similarly made of an
electrolytically inert metal, stainless steel being
preferred. The positive electrode active surface is
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advantageously unpolished to enhance the adherence of
the coagulated colloid thereon.
The colloid generally used is a linear
colloid of high molecular wei~ht, that is, one having a
molecular weight comprised between about lO,OOO and
about 1, 0~0, 000, preIerably ~etween 100,000 and 600,000.
Examples of suitable colloids include natural polymers
such as albumin, gelatin, casein and agar, and synthetic
polymers such as polyacrylic acid, polyacrylamide and
polyvinyl alcohol. Water is preferably used as the
medium for dispersing the colloid to provide the desired
colloidal dispersion.
The colloidal dispersion also contains a
soluble electrolyte which enables the water to have a
greater conductivity. Examples of suitable electrolytes
include chlorides and sulfates, such as lithium chloride,
sodium chloride, potassium chloride, calcium chloride,
nickel chloride, copper chloride, ammonium chloride
and manganese sulfate. Since the speed of electro-
coagulation is affected by temperature, the colloidaldispersion must be maintained at a substantially cons-
tant temperature in order to ensure a uniform image
reproduction.
The selective energizing of the negative
electrodes can be effected by sweeping such electrodes
and transmitting electrical pulses to selected ones
thereof during sweeping. These electrical pulses can
be varied either in voltage or time from one electrode
to another so as to correspondingly vary the amount of
coagulated colloid adhered onto the positive electrode
active surface. This enables one to form dots of
varying intensities and thus to reproduce the half-tones
of an image~
A-fter eoagulation of the eolloid, any remain-
ing non-coagulated colloid is removed from the positi~e
electrode aetive surfaee, for instanee by seraping the
surfaee with a soft rubber squeegee, so as to fully
uncover -the coagulated colloid.
In order to provide a monoehromie or poly-
chromic image, the dots of coagulated colloid obtained
in step (c) of the method according to the invention must
be colored with a coloring agent and the coloring OI
the colloid is effected either before or after the
eoagulation thereof in step (e) depending on whether
the coloring agent used is a pigment or a dye. Where
the eoloring agent is a pigment, the eoloring of the
colloid is effeeted prior to coagulation by admixing
the pigment with the colloidal dispersion so as to
obtain upon the coagulation of the colloid in step (c)
the desired dots of eolored, coagulated colloid. These
are treated after removal of any non-coagulated eolloid
with a eolloid softening agent so as to maintain the
eolored, coagulated eolloid in a softened state for
enabling the pigment to be subsequently transferred
onto the end-use support in step (f). Examples of
suitable colloid softening agents inelude glycerol,
ethylene glyeol, sorbitol and formamide.
On the other hand, in the ease where the
eoloring agent is a dye, the eoloring of the colloid
is effeeted after eoagulation by applying to the dots
of eoagulated eolloid obtained in step (e), after
removal of any non-eoagulated colloid, a liquid
coloring medium containing the dye and having substan-
tially the same eonstant temperature as the eolloidal
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dispersion, -thereby obtaining the desired dots of
colored, coagulated colloid. In this case, the end-use
support utilized in step ~f) must be coated with a
wetting agent which is a solvent of the dye for enabling
the dye to be transferred onto the end-use support.
The end-use support can be gelatinized paper or any
ordinary paper, including uncoated paper such as bond
paper and coated paper such as synthetic resin-coated
or kaolin-coated paper. If gelatinized paper is used,
the wetting agent must also act as a gelatin softening
agent for conditioning the gelatinized paper to receive
the dye, examples of suitable wetting and gelatin
softening agents are water and aqueous solutions of
acetic or citric acid, or an alkali metal salt thereof
such as sodium acetate. If bond paper or synthetic resin-
coated or kaolin-coated paper or the like is used, the
coloring medium must further contain a colloid softening
agent so as to maintain the colored, coagulated colloid
in a softened state and thus allow transfer of the dye
onto such type of end-use support. The colloid softening
agent is preferably glycerol, ethylene glycol, sorbitol
or formamide, whereas the wetting agent used for coating
the end-use support is preferably methanol, ethanol,
isopropanol, acetone or formaldehyde. Preferred combi-
nations of electrolytically coagulable colloid andcoloring medium therefor are ones in which the colloid
is polyacrylic acid or polyacrylamide and the coloring
medium comprises an aqueous solution containing a water-
soluble dye and a colloid softening agent selected from
the group consisting of glycerol, ethylene glycol and
formamide.
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The liquid coloring medium is advantageously
applied transversely of the belt by me~ns of a shower
or horizontal spray of the coloring medium, excess
coloring medium being allowed to drain.off the belt by
gravity so as to be collected for recycling after
removal of resi~ual non-coagulated colloid entrained
with the coloring medium.
Where a polychromic image is desired, steps
(a) through (f) of the above-described method are
repeated several times to define a corresponding number
of printing stages each using a coloring agent of
different color and to thereby produce several diffe-
rently colored images of coagulated colloid which are
transferred onto the end-use support in superimposed
relation to provide the desired polychromic image.
The printing method and apparatus according
to the invention enables to produce per print of 8 l/2
x ll inch about 4,000,000 dots of colored, coagulated
colloid of varying intensities per color with a reso-
lution of about 40,000 dots per square inch and to
provide a printed copy at a rate of one copy every
second, with either a monochromic or polychromic image.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the inven-
tion will become more readily apparent from the following
description of preferred embodiments thereof as illus-
trated by way of examples in the accompanying drawings,
in which:
Figure l is a schematic top view of a printing
apparatus according to a preferred embodiment of the
invention, comprising four printing units each using a
coloring agent of different color,
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Figure 2 is a fragmentary part-sectional view
of a printing unit showing details of the printing head,
Figure 3 is a fragmentary view taken along
line 3-3 of Fig. 2, showing the positive electrode in
the form of a belt,
Figure 4 is a fragmentary part-sectional view
taken along line 4-4 of Fig. 2,
Figure 5 is a fragmentary view taken along
line 5-5 of Fig. 2,
Figure 6 is a fragmentary part-sectional top
view showlng how the printing head can be adjusted
to permit registration of the colored images produced
by the printing units,
Figure 7 is a fragmentary elevation view of
the negative electrodes arranged in rectilinear align-
ment'
Figure 8 is a fragmentary part-sectional view
taken along line 8-~3 of Fig. 2;
Figure 9 is a schematic view of the scanner
system used for scanning the image to be reproduced,
Figure 10 is a schematic diagram showing how
the signals of information provided by the scanner are
processed,
Figure 11 is a fragmentary part-sectional
elevation view showing the paper feeder mechanism used
for feeding individual sheets of paper to the printing
apparatus;
Figure 12 is a part sectional top view of the
paper feeder mechanism shown in Fig. 11,
Figure 13 is a schematic top view of a printing
apparatus according to another preferred embodiment of
the invention, showing a different arrangement of the
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printing units, and
Figure 14 is a view similar to Fig. 13 but
showing in part a further preferred embodiment of the
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring first to Fig. 1, there is illus-
trated a printing apparatus comprising four identical
printing units 20 arranged in tandem relation, but
each using a coloring agent of different color. In the
1~ embodiment shown, the first printing unit 20A at the
right of the figure is adapted to print in black color,
the second printing unit 20B in cyan color, the third
printing unit 20C in magenta color and the fourth
printing unit 20D in yellow color. Individual sheets
of paper 22 are fed from a stack 24 by a feeder mecha-
nism (not shown) and transported to the printing units
20 by means of a conveyor system generally designated
by reference numeral 26. me sheets once imprinted
with a desired image are discharged from the apparatus
and pile up to form another stack 24'. A scanner 28 is
provided for scanning the image to be reproduced.
Each printing unit 20 comprises a printing
head 30 adapted to produce on the surface 32 of a
positive electrode 34 in the form of an endless belt
dots o~ coagulated colloid of varying intensities
representative of the desired image. me belt 34 is
disposed with its surface 32 extending vertically and
is displaced along a closed horizontal path in the
direction shown by the arrow by means of a vertically
disposed drive roller 36 and three vertically disposed
guide rollers 38,38' and 38" which are idler or tension
drive rollers. A horizontal spray system 40 is provided
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for applying a liquid coloring medium transversely of
the belt 34 to color the dots of coagulated colloid,
excess liquid coloring medium being removed from the
belt 34 by a soft rubber squeegee 42. The dots of
colored, coagulated colloid on the surface 32 of the belt
34 are then pressed into contact with a sheet of paper
22 conveyed by the conveyor system 26, by means of the
roller 38', thereby causing transfer of the coloring
agent onto the paper and imprint of the latter with the
desired image. A roller 44 with an abrasive surface is
provided to remove any remaining coagulated colloid from
the surface 32 of the belt 34 and to thus clean the sur-
face 32 prior to passing by the printing head 30 once
again.
As shown, the conveyor system 26 comprises an
endless conveyor belt 46 adapted to convey individual
sheets of paper into position for being successively
imprinted with the colored images by the printing units
20A, 20B, 20C and 20D. The conveyor belt 46 is moved
with its transport surface 48 extending vertically along
a closed horizontal by the drive rollers 50 while being
maintained under tension by means of the tension rollers
52. It is displaced about an evacuated chamber 54 having
a perforated vertically extending wall 56, in frictional
moving engagement with the perforated wall 56. The belt
46 is also perforated to permit the sheets of paper 22
to adhere by suction to the transport surface 48. The
chamber 54 which is maintained under permanent vacuum
via the holes 58 includes two separate compartments
54A and 54B in which the vacuum is controlled indepen-
dently of the chamber 54 via the holes 60 and 62,
respectively. The compartment 54A is evacuated only
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when the paper feeder mechanism which is shown in
Figs. 11 and 12 is actuated so as to assist in the
transfer of a sheet of paper 22 from the stack 24 onto
the transport surface 48 of t,he conveyor belt 46. In
the compartment 54B, on the other hand, the vacuum is
replaced by air pressure when the sheet of paper 22
once imprinted arrives at the position shown in broken
lines so as to eject such a sheet from ~he belt 46, the
sheet thus ejected being guided by conventional guide
means (not shown) to pile up on the stack 24'.
Turning to Figs. 2-8 and more particularly
to Figs. 2, 4 and 5, the printing head 30 of each
printing unit 20 comprises a body 64 secured to
a vertically extending support rod 66 and provided
with a plurality of negative electrodes 68. The
negative electrodes 68 are electrically insulated from
one another and arranged side-by-side in rectilinear
alignment, as best shown in Fig. 7, these define a
series of corresponding negative electrode active
surfaces 70 which are disposed transversely of the belt
34 and spaced from the positive electrode active sur-
face 32 thereof by a constant electrode gap 72 of the
- order of 50 ~. The printing head 30 further includes
a multi-socket member 74 provided with a plurality of
sockets 76 for receiving and electrically connecting
integrated circuit boards 78 to the negative electrodes
68 via the electrical wires 80. The integrated circuit
boards 78 serve to control the selective energizing
of the electrodes 68 and are operative to transmit to
the latter electrical pulses which are modulated in
voltage or time.
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I'he drive roller 36 used to move the belt 34
along a closed horizontal path is fixedly connected to a
shaft 82 which is rotatably mounted to the frame 84 and
driven at substantially constant speed by a motor (not
5 shown) for rotation of the rol:ler 36 about the center
axis 86 in -the direction shown by the arrow in Fig. 2.
In order -to transmit the desired movement to the belt
34, the roller 36 is provided adjacent its upper end
with a plurality of radially spaced-apart teeth 88 engag-
10 ing in corresponding holes 90 formed in the belt 34 andspaced along the upper longitudinal edge thereof, as best
shown in Figs. 3 and 5. The drive roller 36 is located
opposite the negative electrodes 68 with the belt 34
therebetween, the center axis 86 of the roller 36
15 extending substantially in-parallel alignment with
the electrodes 68.
As shown in Figs. 2 and 5, the body 64 of the
printing head 30 is formed with three injection nozzles
92 for continuously injecting under pressure the
20 necessary liquid colloidal dispersion onto the surface 32
of the belt 34 transversely thereof and adjacent the
electrode gap 72 so as to press the belt 3~ against the
drive roller 36 and thereby maintain the required cons-
tant gap, the colloidal dispersion being fed to the
25 nozzles 92 via the conduits 94. In this manner, the
electrode gap 72 is continuously supplied with fresh
colloidal dispersion and thus any gas bubbles generated
as a result of electrode polarization are removed by
being entrained with the excess colloidal dispersion
30 which is allowed to drain off the surface 32 into the
drain pipe 96. After electro-coagulation of the colloid
contained in the colloidal dispersion and formation of
the do-ts of coagulated colloid representative of a
desired irnage on the surface 32 of the belt 34 opposite
-the electrode active surfaces 70 of the energized
negative electrodes 68, any remaining non-coagulated
col]oid is removed from the surface 32 by means of a
soft rubber squeegee 98 and combined with the excess
colloidal dispersion drained off the belt 34 by gravity
. and flowing into the drain pipe 96, so as to be col-
lected and recirculated together with the excess
colloidal dispersion back to the injection nozzles 92.
In order to permit registration of the images
produced by the respective printing heads 30 of the
printing units 20, the vertical rod 66 to which the
body 64 of each printing head is secured is fixedly
mounted to upper and lower members 100 which are
pivotally connected to the drive shaft 82 and the
body 64 is provided with a projection 102 extending
between two T-shaped bars 104 fixed to the frame 84 and
each carrying a screw member 106 so that the position of
the negative electrodes 68 can be adjusted relative to
the center axis 86 of the drive roller 36. Fine adjust-
ment of the screw members 106 causes the members 100
carrying the body 64 to slightly pivot about the shaft
82 and thus the body 64 to pivotally move with the nega-
tive electrodes 68 being displaced relative to the
center axis 86 of the roller 36, as best shown in Fig. 6.
The dots of coagulated colloid produced on
the surface 32 of the belt 34 are colored by means of
the horizontal spray system 40 which is adapted to
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apply a liquid coloring medium transversely of the belt
34, when use is made of a dye as coloring agent. As
shown in Fig. 8, the spray syslem 40 comprises a vertical
tube 108 provided along the length thereof with a
plurali-ty of spaced-apart spray apertures 109 for direct-
ing a spray of liquid coloring m_dium ont~ the surface
32, the liquid coloring medium being fed via the conduit
110. Excess coloring medium is allowed to drain off the
belt 34 by gravity and is collected in the trough 112
for recycling after removal of residual non-coagulated
colloid entrained with the coloring medium, for instance
by ultra-filtration or chemical precipltation. Examples
of suitable dyes which may be used to color the coagu-
lated colloid with the spray system 40 after electro-
coagulation are the water soluble dyes available fromHOECHST such as Duasyn Acid Black (color index No. 194) for use
in the black printing unit 20A and Duasyn Acid Blue (color index
No. 1) for use in the cyan printing unit 20B, or those available
from RIEDEL-DE~N such Anti-Halo Dye Blue T. Pina for use in the
cyan printing unit 20B, Anti-Halo Dye AC Magenta Extra
VOl Pina for use in the magenta printing unit 20C and
Anti-Halo Dye oxonol Yellow 1~. Pina for use in the
yellow printing unit 20D.
On the other hand, where use is made of a
pigment as coloring agent, the coloring of the colloid
is effected prior to electro-coagulation by admixing the
pigment with the liquid colloidal dispersion injected
through the nozzles 92 so as to obtain upon coagula-
tion of the colloid dots of colored, coagulated colloid.
In this case, the horizontal spray system 40 is of
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... ..
course not used to apply liquid coloring medium, but
rather serves to apply a colloid softening agent such
as glycerol, ethylene glycol, sorbitol or formamide in
order to maintain the colored, coagulated coiloid in a
5 softened state and thus enable the pigment to be sub-
sequently transferred onto the pa~r 22 conveyed by
the conveyor belt 46, excess colloid softening agent
being removed from the surface 32 of the belt 34 by the
squeegee 42 shown in Fig. 1. Examples of suitable
10 pigments are those available from HOECHST such as
Colanyl or Flexonyl Black (color index No. 7) for use in the black
printing unit 20A, Colanyl or Flexonyl Blue (col~r index No. 15-3)
for use in the cyan printing unit 20B, Colanyl or Flexonyl Violet
(color index No. 23) for use in the magenta printing unit 20C and
Colanyl or Flexonyl Yellow (color index No. 126) for use in the
yellow printing unit 20D.
,
After transfer of the coloring agent contained
in the dots of colored, coagulated colloid adhered to
the surface 32 of the belt 34 onto the paper 22 by means
of the roller 38' shown in Fig. 1, the belt 34 passes
20 around the abrasive roller 44 which rotates in a direc-
tion opposite to the direction of rotation of the drive
rolIer 36 for increasing the frictional engagement of
the abrasive surface 114 of the roller 44 with the
surface 32, as best shown in Fig. 2. In this manner,
25 any remaining coagulated colloid is removed from the
surface 32 which is thus cleaned prior to passing
through the electrode gap 72 once again. The belt 34
is also continuously washed with a washing liquid such
as water applied transversely of the belt by means of
30 the shower elements 116, the washing liquid entraining
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1~,79~
particles of coagulated colloid removed by the abrasive
roller 44 as it drains off the belt 34 by gravity to
collect in the trough 118 for recycling. Excess washing
liquid is removed by the pair of squeegees 120.
Figure 9 schematically illustrates the scanner
system 28 used for scanning the image to bY ~eproduced.
As shown, the scanner 28 comprises a multi-element opti-
cal lens 122 for reading the document 124 placed on the
transparent window 126 and of which the image is to be
reproduced, The beam of light issuing from the lens 122
is divided into three components of equal light intensi-
ty by the mirrors 128, 130 and 132, the mirrors 128 and
130 being partially reflecting mirrors and the mirror
132 being a totally reflecting mirror. The mirror 128
is adapted to reflect 33 1/3% of the light intensity
onto the red filter 134 to provide a red-filtered image
of reduced dimensions while allowing the remainder of
the light intensity, i.e. 66 2/3%, to pass through for
being reflected by the mirror 130. The mirror 130 in
turn reflects 50% of the incoming light intensity onto
the green filter 136 to provide a green-filtered image
of reduced dimensions while allowing the remainder of
the light intensity, i.e. 33 1/3%, to pass through for
being totally reflected by the mirror 132 onto the blue
filter 138 to provide a blue-filtered image of reduced
dimensions. The red, green and blue-filtered images of
reduced dimensions thus produced are sensed by respective
linear image sensors 140 fixed to a common support 142.
Each image sensor 140 typically comprises 1728 CCD
(charge coupled device) elements which transform light
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into an electrical charge and provide a 200-points-per-
inch resoluti~n across 8.5 inches. As an e~ample of
such an image sensor, use can be made of the TC 101 line
image sensor available ~rom TEXAS INSTRUME~TS INC. The
support 142 is displaced back and forth in the direction
of the arrow to provide a mechanical scanning o~ the
color-filtered images by the image sensors 140 which
in turn electronically scan the images in a direction
normal to the direction of mechanical scanning. Each
of the three image snesors 140 will thus deliver a
signal of information for printing a fundamental color
image by each of the independent printing units 20, the
image sensors asscciated respectively with the red,
green and blue filters 134, 136 and 138 delivering
signals of information for printing respectively in the
cyan, magenta and yellow colors.
As shown in Fig. 10, the signals of informa-
tion delivered by the three image sensors 140 of the
scanner 28 are fed to a central processing unit 143
which is connected to the printing heads 30 of the black,
cyan, magenta and yellow printing units 20A, 20s, 20C
and 20D. The central processing unit 143 determines
a composite signal corresponding to the lowest common
signal delivered by the three image sensors 140, which
composite signal provides the information for printing
in black by the black printing unit 20A. All four
signals of information for printing respectively in
black, cyan, magenta and yellow are amplified prior to
being transmitted respectively to the black, cyan,
magenta and yellow printing units 20A, 20B, 20C and 20D
for activating the printing heads 30 thereof. The
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central processing unit can also be fed with signals
of information originating from different sources, such
as digital computers, modem phone lines and televideo
equipment, -the scanner 28 is of course deactivated
for these applications.
Turning to Eigs. l:L and 12 which illustrate
the paper feeder mechanism utilized for feeding indivi-
dual sheets of paper 22 ~rom the stack 24 to the conveyor
system 26, such a paper feeder mechanism which is
generally designated by reference numeral 144 is seen to
comprise two movable suction members 146 each fixedly
connected to a chain 148 which itself is driuen along a
triangular path by sprocket wheels 150 at the corners of
the triangle. Each suction member 146 is provided with
suction holes 152 for adhering by suction a sheet 22
and is connected to a vacuum outlet 154 by means of a
flexible conduit 156. As shown, the suction members
146 are operative to pick up the uppermost sheet of the
paper stack 24 supported at a slight angle by the plat-
form 158 and maintained at a constant level by means of
the lifter 160 coupled to a level sensing device 162,
and to transport the sheet thus picked up to a transfer
position represented in brokenlines whereat the sheet
is positioned adjacent the conveyor belt 46 of the
conveyor system 26 and faces the transport surface 48
of the latter. A blower 164 is also provided for
applying air pressure against the sheet 22 at the
transfer position so as to displace same onto the
transport surface 48. At the same time as the blower
164 is activated, the compartment 54A is evacuated
~ ..
1;~7'3~
in order to assist in displacing the sheet 22 on the
conveyor belt 46 which is perforated and in continuous
frictional moving engagement with the wall 56 provided
with perforations 166, and also cause the sheet 22 to
adhere by suction to the transport surface 48. Ihe sheet
22 is retained in stationary position on the continuously
moving belt 46 in frictional sliding engagement therewith
by means of two vertically spaced retractable stop mem-
bers 168 which are retracted by the solenoid-type devices
170 when order is received to release the sheet.
The printing apparatus described above can
print a monochromic or polychromic image and can be
operated in either monomode to print an image on a single
copy or in multimode to print the same image on several
copies. Thus, when it is desired to print in monomode a
monochromic image, a single sheet of paper 22 is fed to
the black printing unit 20A which is activated to print
in black whereas the cyan, magenta and yellow printing
units 20B, 20C and 20D are inactive to print, in multi-
mode, several sheets of paper 22 are fed one at a timeto the black printing unit 20A which then functions
non-stop until all the desired copies are printed. On
the other hand, when a polychromic image is desired,
all printing units 20A, 20B, 20C and 20D are operative
to print,
Figs. 13 and 14 illustrate alternative embodi-
ments. As shown in Fig. 13, the path defined by the
conveyor belt 46' of the paper conveyor system 26'
includes a pair of parallel rectilinear portions and
the printing units 20' are arranged along both recti-
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