Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention is concerned generally with
electrostatic copying machines and a method in which
the same document is to be repeated in multiple copies.
Two types of presently used electrostatic
copying machines are in gereral use, one operating on
the basis of xerography and the other on the basis o~
that which is known as electrofax. The xerographic device
provides an electrophotographic member in the form of an
amorphous selenium drum based upon metal, the selenium
surface being charged, exposed to an image, toned and
the toned image trans~erred to a receptor which usually
consists of ordinary paper. After transfer, the image
is fused to the paper by a heat lamp. The electrofax
device provides an electrophotographic member in the form
! 15 of a sheet of conductive paper carrying a coating of
zinc oxide in a resin matrix, the coating being charged
and exposed to projected image after which the entire
electrophotographic member is moved through a liquid
toner bath and fused in the latter step of which it is
dried. The entire member becomes the copy of the docu-
ment or article which has been copied.
In both cases, when multiple copies are required,
the apparatus recycles, passing through the functions of
charge, expose and tone. IIn the case of the xerographic
apparatus the electrophotographic member is caused to
transfer the toned image to the receptor, the receptor
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is fused and dispensed into a bin, the member is cleaned
and discharged and the mechanism st:arts all over again
to charge, expose, tone, etc. In the case of the
electrofax apparatus, obviously since the copy is the -
electrophotographic member itself, the machine must go
through the complete cycle from the very beginning and
through to the dispensing of the toned electrophoto-
graphic member for each copy.
The charge which is placed upon the surface of
the known type of electrophotographic member as used
in the xerographic and electrofax apparatus is selective-
ly dissipated by the light which is projected onto the
surface to form the latent image, leaving a latent
image of primarily positive charges in the first case
and negative charges in the second case. When toned
by applying the fine particles of suitably polarized
carbons, resins, etc. constituting modern toners, the
toner particles neutralize or absorb the charges con-
stituting the latent image. If these particles are re-
moved mechanically, as by transfer to a receptor, sub-
stantially no charge of any consequence remains on ~he
surface of the electrophotographic member. Either
the toning neutralizes the charge or absorbs it,
probably the former~
Using this type of electrophotographic member
it is seen that Xnown electrostatic copying machines
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must be complex and expensive, must have e~pensive,
long duty cycles and must have slo~ throuyhputs. The
rate of reproduction is limited by the length of a com-
plete duty cycle.
Accordingly, the invention provides a method
of producing multiple copies of an object being imaged
on the photoconductive coating of an electrophotographic
member which comprises establishing a uniform electro-
static charge at least at the surface of the photocon-
ductive coating, exposing the charged coating to a pro-
jected image of the object to achieve a latent charge
image thereof, toning the coating to achieve a visible
toned image, transferring the visible toned image to a
receptor to achieve a copy of the projected image and
repeating only the last two steps for at least another
time to provide at least a second copy of the projected
image, excluding repeated performance of the charging
and exposing steps, all of the steps of said charging,
exposing, toning and transferring being carried
on in the absence of ambient light on the coating.
The invention further provides apparatus for
carrying out said method comprising a charging station
having charging means, an exposure station having image
projecting means, a toning station having toning means,
an image transfer station having transfer means, means
for mounting an electrophotographic member as afore-
described with coating arranged to~be subjected to said
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charging, projecting, toning and transfer means, trans-
port means for transporting the electrophotographic mem-
ber and the respective stations relative to one another
in the named consecutive order w~lereby to subject the
coating seriatim to the operation of the means at said
stations, means for moving a receptor into the transfer
station to have such toned image as carried by said
member transferred to said receptor each time said
transfer means operates but on an additional respective
receptor for each subsequent toned image transfer, said
transport means being arranged to repeat at least once
the said transporting of said member relative to at
least the toning and transfer stations and to subject said
coating for such repeat to the operation of said toning
and transfer means but not to the operation of said
charging and projecting means and means for controlling
the operation of all of said previously mentioned means
in predetermined timed relation to one another.
The preferred embodiments of this invention
will now be described, by way of example, with reference
to the drawings accompanying this specification in which:
Figure 1 is a highly schematic view and block
diagram combined, showing apparatus of the invention
. capable of carrying out the method thereof;
Figure 2 is a block diagram showing by way of :
progression the steps constituting generally the method
of the invention and
,
Figure 3 is ~ frag~entary section~l view on a
highly exaggerated scale oE an electrophotographic
member suitable for use with the invention.
The method of obtaining multiple copies
electrophotographically according to the invention
preferably employs an electrophotographic member which
has a photoconductive coating that does not lose charge
to toner. In such a member, the cl~arge procuces a
field or what can be considered an enormous number of
fields, on the surface of the photoconductive coating~
to which suitably polarized toner particles are attract-
ed. In contrast with the type in which ions sit on the
surface, when toner particles are removed from the sur-
face, there is no longer an integrated charge remaining
on the surface. On the other hand, when the toner
particles are removed from the photoconductive coating
th-at has the charge at or below the surface, the
charge is not affected. Accordingly, such charge on the
latter type of coating, whether it is a uniform charge
or is represented by a latent image of an object being
copied, will persist irrespective of the number of'
times it is toned and the toner removed until the quality
of the image deteriorates due to the dark decay character--
istic of the coating. This latter is not a function of
the application or removal of toner particles but is a
physical concept inherent in the;coating~itself.
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One electrophotographic member and coating
which is ideally suited for the inventio~ herein has
a photoconductive coating comprising a thin film,
microcrystalline, inorganic, dense, sputtered semi-
conductor material and is beleivecl to produce anisotropy
of a remarkable nature. The crystallites forming the
coating are orthogonally oriented relative to the
substrate and thus are believed to produce a practically
infinite number oE individual fields at their apices
on the surface. The constitution of the coating is
such that the charge applied thereto is believed to
enter into the coating and be trapped in suitable lo-
cations therein, being neutralized or caused to re-
combine only by radiation during exposure and not by
surface contact with charged toner particles. when
the toner particles are removed as by transfer the
charged increments are not affected: hence the same ;
latent image still remains and may be again toned and
transferred ôver and over again many times without re-
charging and re-exposing.
The method of the invention shall be explained
with reference to Figure 2 which shows a series of blocks
representing a flow chart of steps from left to right.
Block 10 represents two steps combined in order to render
the diagram easy to follow. Actually these two steps ara
normally performed seriatim with the electrGphotographic
- member being first charged by corona or the like and
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thereafter being exposed to the illumination produced
by projecting the image of an object onto the electro-
photographic member, that is, onto the photoconductive
coating thereof. Thus block 10 is called "charge ~
Expose." The next following blocX 12 is marked "Tone
& Transfer - 1" this being the next two following steps
ln the procuction of a copy of the object. The surface
of the photoconcuctive coating is toned either by dry
or liquid toner which adheres in accordance with the
latent charge image and thereafter a receptor member
such as a sheet of paper is pressed against the coat-
ing and it picks up the toner to transfer the toned
visible image to the surface of the paper. At least, the
exposing and transfer is effected in the absence of
an electrical field.
There can be a subsèquent fusing or fixing
step but also, the toner can comprise a suspe~sion in
a solvent which readily evaporates and leaves the toned
image self-adhering without the need for fixing. Both
types of toner are usefuL and for simplicity, no fixing
step is referred to in the diagram of Figure 2. It is
presumed to be there if needed. In such case it would
follow after the block 12.
In the known systems and methods such as
exemplified by xerography the next step following the
tone and transfer represented by block 12 would have
to be again charge and expose if one wanted multiple
copies. Each copy would go through the same duty cycle,
requiring energizing of the high voltage corona circuit,
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operation of the optieal mechanism and energiZatiOn
of the proj~ctor lamp and circuit. In addition, the
mechanical apparatus needed to return mechanisms to
initial positions at the beginning of the procedure
could be complex. Thus, blocks 10 and 12 so Ear as
described above are known. ~he only difference between
the prior art and the invention is represented by the
numeral "l" in the blocks 10 and ]2.
The presence of the numeral "l" in blocks 10
and 12 is intended to signify that the pair of steps
of block l2 will produce the first copy from the first
pair of steps of block 10. The next block is 14 and
again it is designated "Tone and Transfer" but this
block is marked by the numeral "2". What this means
is that immediately after the image has been trans-
ferred in block 12 it is again toned and the second
image transferred to another receptor. This has been
done out of the same first latent image achieved through
the charge and expose steps of block 10.
The same two steps of tone and transfer are
repeated over and over again, as indicated by the broken
lines at 16 until the user decides he has enough copies.
The last copy is then produced by the block 18 which is
marked "Tone &~;Transfer - n", meaning that n copies
have been made. If there has been no substantial decay
of the charge due to the inherent dark decay characteristic ~-
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of the electrophotographic member when the nth copy
has been produced, the process may be stopped at the
block 18. If on the other hand the user wants more
copies than he has made by the process described and
in his judgment, or in the judgment of a suitable
densitometer measuring the copies it appears that copies
after the nth will not be acceptable, he can again
charge and image the electrophotographic member (block
20) and following that tone and transfer as described
above (blocks 22 and 24~. This can continue as long
as desired. ;
It is noted that the blocks 22 and 24 are
marked "Tone & Transfer - n+l" and "Tone & Transfer
-n+2". The signigicance of this is that the number of
copies which follow after the nth copy will be n+l, n+2,
etc., but the group thus identified will be the second
group, deriving from the first renewal of the charge
and exposure which,~of course, is the second such charge
and exposure. This may continue so long as desired.
The requirements for apparatus for carrying
out the method described above can be very simple and
economical~ Either fully, or partially automatic, ap-
paratus are contemplated. Likewise, the apparatus can
be arranged for linear movement or rotary movement, and
can be quite sophisticated.
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In Figure l there is diagrammed in a highly
simplified form a rotary typ~ of apparatus 30 for carrying
out the invention. The electrophotographic member
, 32 is mounted on a suitable rotary cylinder 34 driven
by some rotational mechanism at a controlled speed.
This is indicated by the broken line 36 which extends
to the block`38. Block 38 is marked "Synchronize and
Speed control'~ and as will be seen it represents con-
trols and circuitry, manual, automatic or a combination
thereof. It can represent power sources, drive and
- speed devices, etc.
A charge device 40 operated through the channel
41 from the control or programmer 38 is disposed on the
left of the cylinder 32 and charges the member 32 as
the cylinder rotates in a clockwise direction indicated
by the arrows. The charging can be performed at a charg-
ing station 42 and from this station, the member 32 is
carried around to the top of the cylinder 34 to exposure
station 44. Here a suitable light source 46 energized ~ ~ -
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through the channel 48 illuminates an ob~ect 50 which
in this case can comprise a transparency of a scene or
document. The projected material is passed through a
suitable opticaL train 52 and illuminates the charged
surfacé of the electrophotographic member 32 at the
proper timed relationship when the member-32 arrives at
the exposure station. The resulting latent image can
be applied by momentarily stopping the cylinder 34 or by
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suitable rocking mechanisms and op~ics which apply
the image during movement oE member 32 past the ex-
pOSure station ~4.
The now-exposed member 32 moves to the toning
station 54 at which there is a toning mechanism 56 con-
trolled from the controL or programmer 38 by way of the
channel 58. After toning, the member 32 is rotated
down to the transfer station 60 at which poi~t a back-
up roller 62 is located. A paper supply 64 synchronized
in operation through the channel 66 is arranged to feed
a receptor such as a sheet of paper 68 along the paper
feed 70 into the nip between the back-up roller 62 and
the cylinder 34 just at the time that the-toned member
32 arrives at the nip. As the paper member 68 goes
through the nip the toned image is transferred to the
paper surface and the completed paper copy falls into
the bin 72. A stack of copies is shown at 74. If needed,
fusing of fixing can be effected at 76, while the paper
copy is on its way to the bin 72 or even in the bin.
The member 32 now is rotated around past the
charging station 42 and the exposure station 44 but in
the meantime, the control~device 38 has deenergized the
charging device 40 and the projecting lamp 46 ~as well
as any associated mechanisms) so that the toning station
is reached without anything being done to the member 32.
The toning mechanism 56 is operated, the toned image
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transferrerl to the n~xt sheet oE paper 68 and the par-
tial duty cycle (i . e ., with~ut charging and e~posing)
is repeate~ again and again. Sinc~ there need be no
steps other than tone and transfer, the control device
38 can automati~ally increase the speed of rotation of
the cylinder 34 and synchronize operation of the toning
mechanism 56 and paper feed 70 to suit.
The production of copies can continue until thé
user sees that the quality has deteriorated. He can
stop the action if he has sufficient copies before
this occurs. If not, he can operate the control device
manually to restart the charge mechanism 40 and the ex-
posure mechanism and lamp 46 so that he can commence a
second series of copies. Alternatively, he can do the -
latter automatically.
For automatic operation, a densitometer repre-
sented by the spot projector 78 and photoresponsive
device 80 (such as a photocell) is arranged to monitor ~-
the copies in the bin 72. when the density of the copied
image deteriorates to produce a signal (or absence of
signal) when compared with some adjustable standard (not
shown) through the channel 82, the control mechanism 38
is arranged to cause charge and exposure of the member
32 for one revolution only.
Figure 3 shows the electrophotographic member
which is ideally suited for use as the member 32. There
is a substrate 90 which is of a synthetic resin (Mylar
the trademark of E.I. DuPont Denemours Co. of Wilmington,
Delaware, U.S.A. for polyethylene terephthalate plastic)
about .005 inch thick having an ohmic layer of
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tin-indium oxide 92 sputtered ther~on of ~ thickness of
several hundred Anystroms. Upon this ohmic layer 92
is a dense, microcrystalline, sputtered coating 94
of cadmium sulfide about 2500 to 5000 AngstrOms thick.
The cadmium sulfide comprises the photoconductive coat-
ing of the type described above and is one of several
examples of inorganic, thin film coatings that will
produce the characteristics mentioned. The principal
characteristic so far as this invention is concerned is
the ability to hold charge at or below the surface o~
the coating rather than sitting on the surface so that
toner particles applied and removed will not substantially
affect the charge.
Obviously ~he steps of the invention are best
carried out in darkness to delay dissipatLon of charge
by any means other than inherènt dark decay. Shrouds
for the apparatus are presumed and are symbolically
represented at 96. The reference to "ambient light"
means external light not including the exposure means 44.
The particular electrophotographic member 32
described can be toned and tran=ferred in about a second
or less time~ Once the photoconductive coating 94 has
been charged and imaged (which may require about half a
second or less) the copies can be made at a rate of about - ~-
one a second. If the duty cycle included charge and
expose, the cylinder could rotate at about one revolution
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every two scconds, but since the charge station 42 and
exposure station ~4 ~re not used during the making of
repeat copies, the rate of rotation of the cylinder 34
can be doubled. These exact figures for speed and
rates are only by way of example and are subject to
wide variation. The number of copies made from a
single exposure can be from several to hundreds, de-
pending on the materials, toners, etc.
As indicated previously, the operation of the
apparatus and method can be carried out using a linearly
moving mounting for the electrophotographic member 32.
In such case there would be a carriage which recipro-
cates relative to the several stations, but does not
return to the charging and exposure stations when in
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the repeat mode. Thus, assuming that the stations follow
one another along a line, the reciprocal path of the
carriage is half as long in the repeat mode as in the
original full cycle mode.
Arrangements can be made in which the electro-
photographic member is fixed and the apparatus carries
the stations relative to it. Likewise,- the electro-
photographic member could be moved in a cycle which is
both rectilinear and rotary, as for example, on an end-
less recycling belt.
The receptor can be any suitable article to
which the toned image can be transferred, but normally
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it will be a sheet of paper. It could be a long roll
or ribbon of paper which may or may not be cut into
individual members either beEore or after transport.
The paper supply can be a stack of sheets fed off one
at a time.
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