Note: Descriptions are shown in the official language in which they were submitted.
32.'~i
The invention relates electrostatographic copy:ing.
The fo~nation and development of images on the surface of
photoconductor rnaterial by electrostatic rneans is well known. m e basic
xerographic process as taught by C F Carlson in US Patent no 2,297,691
involves placing a uniform electrostatic charge on a photoconducti~e
insulating layerr exposing the layer to a light and shadow image to
dissipate the charge on the areas of the layer exposed to the light and
deve:Loping the res~Ltirlg electrostatic charge pattern unage hy deposlting
on the image a finely divided markiny material referred to in the art as
'toner'. The toner wiLl normally be attracted to those areas of the
layer which retain a charge thereby forming a toner image corresponding
to the electrostatic charge patters. The powder image rnay then be
transferred to a support surface such as paper and perm~nently affixed
to the support by any suitable means such as heat fixing or solvent
fixing. ~lternatively, the powder image may be fixed to the photocon-
ductive layer if elimination of the powder transfer step is desired.
In addition instead of form m g a charge pattern by uniform~y charging a
photoconductor followed by image-wise light exposure, a charge pattern
rnay be formed by directly charging the layer in image configuration.
Other methods are kncwn for applying marking particles to the imaging
surface. Ihcluded within this group are the 'cascade' development
technique disclosed by E N Wise in ~S Patent 2,618,552; the p~wder
cloud development technique disclosed by C F Carlson in US Patent
2,221,776; and magnetic brush process disclosed, for example, in US
Patent 2,847,063
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A liquid technique for developing electrostatic
charge patterns is the liquid development process disclosed
by R W Gundlach in ~S Patent 3,084,043. In this method, a
charge pattern is developed or made visible by presenting
to the image surface a liquid developer on the surface of
a developer dispensing member having a plurality of raised
portions defining a substantially regular patterned surface
and a plurality of portions depressed below the raised
portions. The depressed portions contain a liquid developer
which is maintained out of contact with the electrostato-
graphic imaging surface. When the raised areas of the
developer application are brought into contact with the
imaging surface bearing a charge pattern, the developer
creeps up the sides of raised portions in contact only with
the charged area of the imaging surface, and is deposited
thereon.
In accordance with one aspect of this invention
there is provided an optical system for projecting an image
of an object from an object station, along an optical axis,
to an image receiving member, including: a lens disposed on
said optical axis between said object station and said image
i receiving member to form and project an image of said object
along said optical axis, optlcal means diposed on said
optical axis on the image side of said lens to form at
least two identical images from said projected image and to
direct said identical images to separate portions of said
image receiving member so as to simultaneously form thereon
identical imayes of said object, and developer means adja-
cent said image receiving member to sequentially clevelop
said identically ~ormed images.
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Electrostatographic reproduction methods and apparatus according
to -the invention will now be described by way of example with reference
to the accompanying drawings in which:
,~
Fig 1 is a sche~atic representation of a simplified xerographic
system showing the various major process steps and their relationship ta
one another; and
Fig 2 sh~s diagrammatically the layout of the optical s~stern
of the apparatus.
Referring now to Fig 1, there is shown a xerographic drum r~mber
1 comprising photoconductive imagirg layer of seleniurn coated on a
resilient substrate. In operation, tne xerographic member 1 is charged in
the usual ~anner at charging station 4. The ~ember 1 is then exposed
simultaneously to a light image at a first exposure station 5 and a
second exposure station 6 in order to forrn simMltaneously two charge
patterns. ~oth chc~rging and exposing are disclosed in US Patent 2,297,691.
m e electrostatic images thus formed a~rethen made visible in se~uence at a
developing station 7 where liquid developer is applied to the photoconductive
surface. The developing station 7 coA~prises an applicator roller having a
pattern of recesses on its surface. m e images, no~ visible, are then
transferred sequentic~lly to receiver r~3mbers at a transfer station 9.
At the transfer station 9, paper sheets 11 entralrAed over a roller 11
are pressed irA turn into contact wlth the in~ges on the sur~ace of the
.
me~ber 1 and the images are transferred to the paper sheet 10 to form the
final copies. Any developer material remaining on the xerographic member
1 after the transfer station 9 is removed from the surface of the ~ember
1 by a doctor blade 14. ~eveloper material doctored frcm the xerographic
n~ber is collected in a tray 15. The member 1 is then charged to start
the next sequence of operation.
The apparatus of Fig 1 depicts a typical apparatus and t~pical
Configurations of imaging surface and applicator roller except that more
than one e~posure station is provided for simultaneous e~posure o~ llght
ima~es. It is to be understood that other configurations are possible,
for example, the member 1 could be a belt contacted by a roller at
developing station 7. Li~ewise, other forrns ofdevelopment may be used
such as cascade or maynetic brush development.
'
Referring to Fig 2, a platen 20 supports an original 21 to
be copied. Below the platen 20 an optical scanning system comprises a
full-rate mirror 22 which directs a light image of the original 21 onto t~o
half rate mirrors 23 and 24, at right angles to one another, which direct
in turn the image towards a lens 25. (The position of the mirrors 23 and
24 tcwar~s the end of scan are shot~n dott~dinFig. 2.)
From the lens 2S, the light image is reflected by a ~ir~or 26
towards a mirror 27. Interposed between mirrors 26 and 27 is ca beam-
splitter 28 arranged to reflect one light image ta~ards a mirror 29 and
trclnsmit another light in~ge towards the mirror 27. qwo light images thus
.
!
2~
provided are reflected respectively to exposui-e stations S and 6 by the
mirror 29 and a mi.rror 30.
It will be appreciated that campared to prior art apparatus
which exposes one light image at a time, the described e~odiement can
produce twice the number of copies for example for a given speed of the
member 1.
m e optical path has been chosen such that the angles of
incidence of the light beam are small. Although the angles of incidence ~
couls be arranged to be relatively higher, the lay-out of the optical .
system shown in the drawings is preferred in the described e~bodiment
because the sizes of -the miirrors and beamrsplitter can be kept to a
mini~um. Further, the optical axes of the ~urrors 26 and 30 are in line
with the incident beam from the lens 25 and the optical axis of the mirror
27 is at right angles to the incident beam. This fascilitates adjustments
and simplifies the design of the murror mountings (no~ shcwn).
... ,.,,. . ~ .... ,.,, . ,, .
In another e~bodiement we provide an optical system whic~ directs
three light images sinmltaneously onto the surface of the n~nber 1
enabling the rate of producing co~ies to be further increased. It will be
appreciated that within the scope of the invention four and nxhe
light images of an original be arranged to be simultaneously directed to-
wardsthe member 1 or an equivalent support for a photoconductive layer as
requir.ed. The number of images that can be used s~multaneously is of .
course dependent on the surface area of the photoconductive layer c~nd it
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is intended to be within the scope of the invention that -t~ or more llght
images can be arranged to be directed simultaneously and side by side onto
a photoconductive layer.
~ general, the il~?rov~nent provided by the invention is an
increase in output of copies from any particular electrostatographic copying
system. m e speed oE rota-tion oE a drum, such as member 1, or movement
of a belt, is limited m~inly in practice by mechanical considerations.
The response of the photoconductive layer to light images for example in
prior art apparatus tends to operate well withinits time limitations.
I'hus, having achieved a n~ n speed Eor nember 1 or a belt, and in
the case where a scanning op-tical systern is used the r~ m speed of that
system, no further increase in output of copies is possible. Clearly,
scme gradual improve~ents are to be expected in the operational speeds
but the invention enables the current rate of producing copies to be
increased by around two fold, threefold or more by novelly si~ultaneously
exposing ~o or m~re light images oE a single original.
In ~he described embodiernent, a single developing station is
provided. In other arrangements two, or more, developing stations can be
provided to develope respectively the t~70, or ~ore, electrostatic images
simultaneously rather than sequentially. Iikewlse, two or ~ore, transfer
stations and/or c~arging stations can be provided with such number of
cleaning stations as are then required.
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Further, it will be appreciated that the invention may ~e used 1:
with an electronically controlled writing system in which the light image
is ormed b~ a m~dulated scanning laser bean. In such a case, the laser
beam is directed towards the ~irror 26 and split into t~o (or more) Farts by
a beam splitter such as beam splitter 28. 1 .
Whilst a particular embx~lY~lt of the invention has keen
described above, it will be appreciated that various mc~ifications may
be made b~ one skilled in the art without; departing frcm the scope of
the invention as defined in the appended claIms.
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