Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to electrostatic printing
arrangementsj for reproducing forms or other documents.
Non-mechanicaI printers which operate electrostatically are
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already known. In such printers, charge images of the characters
to be reproduced are derived either electrophotographically or
electrographically on a data carrier. The data carrier can consist
of paper which is to receive the final printed copy or of an inter-
mediate carrier. The charge images on the data carrier are developed
by a so-called toner. If paper is used as data carrier, the deve-
lopment device is directly followed by a so-called fixing device
which serves to fix the developed charge image on the paper, for
example by heating. If 9 however9 in the case of non-mechanical
printing~ an intermediate carrier (e.g. a xerographic drum) is used,
the developed charge images are transferred to paper and fixed only
subsequently. `
In any case, the data carrier must be designed in such manner ~`
that the charge images of characters can be produced upon them.
Accordingly~ in electrophotographic printing, data carriers are used
~- which contain a photo-electric layer in which the charge images of
the characters are produced by action of light.
In electrostatic printers of this type, it is desirable to
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~` construct the image of the document to be reproduced at the instant
~- of the production of the charge images of the characters on the data
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~ carrier. For this, it is necessary that production of the charge
; 25 images is independent of production of the characters on the data
carrier.
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A non-mechanical printer which fulfills the above mentioned
requirements is known. A data mask (e.g. a photo-negative of the
document to be printed) is produced on a scale of 1:1, and is
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~ permanently assigned to the photo-electric data carrier. Using
¦ flash lamps the mask data is transferred onto the data carrier and
~ a charge image is thereby produced. However, this realisation has
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the disadvantage that the form which is to be printed is portrayed
on the data carrier in one exposure and therefore the data carrier
must be appropriately large. ~his constitutes a particular dis-
advantage when photo-conductor-drums are used as data carrier.
An object of the invention is to provide an electrostatic
printing arrangement in which a charge image can be produced in
simpie fashion on a data carrier, and in which the dimensions of
the data carrier itself are not restricted by the size of the
document to be printed.
In what follows, the term "print original" is used to mean
a mask (e.g. a photonegative) of a document to be reproduced.
According to the invention, there is provided an electro-
static printing arrangement comprising: a movable photo-sensitive
data carrier; a rotatably mounted transparent cylindrical roller
arranged to receive a print origlnal(as hereinbefore defined)on
its outer cyllndrical surface and to rotate in synchronism with
motion of the data carrier; a light source extending within and
- longitudinally of the roller; and a screen arranged between the roller
; and the data carrier to determine the portion of data on said print
~ original which is instantaneously to be transferred to the data
¦ carrier, the arrangement being such that the light emanating, in-use,
from the print original is diffused. Preferably, the light source
is a fluo~escent strip lamp arranged to emit diffused light. In one
embodiment~ the roller is spaced from the data carrier, and an
objective lens is arranged between the screen and the data carrier~/
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In a further embodiment, the roller is disposed directly adjacent
the data carrier. Preferably, the roller is provided with a first
gear at one end thereof, the pitch diameter of the first gear
corresponding to the diameter of the roller, there being a second
S gear driven by a motor and engaging with the first gear to drive ~;
the roller. Preferabl~, the second gear is arranged between the
roller and the data carrier.
When it is provided, the print original is preferably to
the same scale as the original document to be reproduced. The peri-
phery of the roller preferably corresponds to the size of the print
original. Preferably, the roller is exchangeable to correspond to
print originals of various sizes, the number of teeth on the first
gear being changed to maintain compatability with the second gear.
The print original miy itself be capable of diffusing light from
said source. ~ -
For a better understanding of the invention, and to show how
the same may be carried into effect,~refererlce will now be made, by
way of example~ to th~ accompanying drawings, 1n whlch O
Figure 1 illustrates a schematic perspective uiew of a
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printing arrangement according to the invention; and
Figure 2 is a plan view of the arrangement of Figure 1.
The F;gures-show a schematic illustration of an electro-
static printing arrangement in which only those parts which are nec-
essary to explain its function have been shown. A photo-electric
drum AT is used as a data carrier. Other devices which are required
for the pr~d~lction of the charge images on the data carrier have not
been shown. The method of production of such charge images of
characters to be reproduced is`known and can be gathered from the
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prior art~
The data carrier AT is in the form of a drum and bears a
photo-electric layer on its outer cylindrical surface. The direction
of rotation of the data carrier AT is indicated by an arrow. Charge
` S images of forms or other documents are to be produced on this data
carrier AT. There is further pr~vided a transparent roller W,
a mask DV arranged on the transparent roller W and forming a print
original of the form or other document and a screen BL lying between
transparent roller W and data carrier AT.
An objective lens OB may also be inserted between the dia-
phragm BL and the data carrier AT. Within the transparent roller W
is arranged a light source L which extends longitudinally of the
roller W. The light source L can be, for example, a fluorescent
strip lamp which emits diffused light. The roller consists, for
example, of acrylic glass.
;;~ The print original may consist of a transparent negative of
~ the document to be reproduced and may reproduce the document on a
;i~ scale of 1:1. The print original is placed onto the outer cylindrical
surface of the rolIer W. When the fluorescent striplamp L illuminates
the inside of roller W, the print original is also~illuminated.
Then light is emitted from Ihe light-transmissive parts of the print
original. The screen BL serves to gate out a part of the light
emanating from the print original D~, and this part falls onto the
data carrier AT. The roller W rotates in synchronism with ~he data
carrier AT so that a charge image of the entire print original DV is
` successive7y built up on the data carrier AT.
The Figures show an objective lens OB arranged between the
screen BL and the dat~ carrier AT. However, it is possible to omit
this objective OB by arranging the roller and screen direct adjacent
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the data carri~r AT. In ~his case, the screen BL must lie very close
to the surface of the data carrier AT~ Only then is it ensured that
the charge image of the print original produced on the data carrier
AT is not distorted~
i 5 If the size of the document to be reproduced is changed, with
-- a scale of 1:1, the slze of the print original DV also changes. The
periphery of the roller W must therefore also be changed correspond-
ingly. The roller W must be arranged so that its distance from the
data carrier AT remains the same.
Figure 2 illustrates how the roller W can be driven~ To this
end a first gear Zl (e.g. a spur gear) is arranged at one end of the
roller W. This gear Z engages with a second gear Z2 which is driven
by a motor M. The pitch diameter of the first gear Zl may correspond
to the diameter of the roller W. If rollers of different diameters
are to be used Ot~ account of different sized print originals, the
pitch diameter of the gear Zl also changes. Therefore, in order to
allow the gear Zl to continue to cooperate with the gear Z2, the
number of teeth on the gear Zl is selected to be such that the
modulus of gear Zl remains constant.
As the distance between the roller W and the data carrier
AT is to be invariant, it is expedient to arrange the second gear
Z2 between roller W and data carrier AT.
~` The exemplary embodiment merely illustrates how charge images
can be produced on the data carrier AT. The development of these
charge images and the transfer to normal paper has not been shown.
However, these non-mechanical print~ng procedures can be gathered
from known devices.
The arrangement is designed in such a way that the light
emanating from the print original is diffused. This ensures that
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no distortion of the original which is to be portrayed occurs on the
data carrier. Diffused light can be produced either -in that the
light source emi;ts diffused light or in that the prlnt original
j itself diffuses the non-diffused light emanating from the light source.
An electrostatic printing arrangement in accordance with the
invention has various advantages :
The production of the print original and the exchanging of
the print original is very simple. It is merely necessary to
produce a negative of the document to be reproduced.
The use of a fluorescent strip lamp provided with a reflect-
ive layer results in good exploitation of light. As a result no
cooling problems occur. Continuous illumination of the print
original avoids the use of flash lamps which must be time controlled
and the use of a complete illumination systemO
Using appropriate rollers, it is possible to process documents
of various sizesO
The arrangement is of very simple construction so that its
production costs ar~e very lowO
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