Note: Descriptions are shown in the official language in which they were submitted.
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A SYSTEM AND METHOD FOR COMPUTER TO PRESS PRINTING
FIELD OF THE INVENTION
The present invention relates to printing systems generally and more
particularly to computer to press printing systems.
BACKGROUND OF THE INVENTION
Printing press systems, such as the ones manufactured and sold by
Heidelberg Druckmachinen of Germany are well known in the art. One drawback of
conventional printing press systems is that the time required to prepare the
printing
system before the onset of actual printing, also termed the "make ready time",
is
relatively long and therefore, it is widely accepted that these systems are
suitable only
for printing large number of copies of the artwork to be printed. Typically,
conventional printing press systems operate to print more than five thousand
copies
is per printing job.
In the conventional printing process, printing is preceded by a "pre-
press" process which generally includes the production of films of the color
separations of the artwork to be printed, the preparation of plates therefrom,
and their
subsequent mounting on the periphery of the printing press. The films are
recorded
by a laser plotter according to the digital representation of the artwork
stored in a
computer used to control the process. Alternatively, plates may be recorded
directly
so as to eliminate the stage of producing them from films.
In the last decade, printing press systems designed for short run printing
has been developed. Typically, short run printing press systems are computer
to
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press printing systems in which the pre-press process and the actual printing
are
carried out by a single system. In these systems, the color separations are
recorded
directly on the printing plates.
Examples of computer to press printing systems are described in U.S.
Patent 4,395,946 to Price and in published European Patent Application
0,512,549 to
Naniwa.
One type of computer to press printing systems is digital offset press
(DOP) printing systems. A typical prior art DOP printing system is illustrated
in Fig.
1 to which reference is now made. The DOP printing system of Fig. 1, generally
io referenced 1, includes a plate cylinder 10, a blanket cylinder 12 and an
impression
cylinder 14. A single beam imaging unit 18 records the color separations of
the
artwork to be printed, typically four color separations of the four process
colors cyan,
magenta, yellow and black (CMYK), on four corresponding printing plates 20,
22, 24
and 26.
After the color separations CMYK are recorded on the printing plates 20,
22, 24 and 26, respectively, each one of the four inking assemblies 30, 32, 34
and
36 apply a corresponding ink on one of the CMYK printing plates. As shown by
the
arrow 37, the inking assemblies may move towards the plate cylinder and away
therefrom to position one inking assembly in a working position according to
the color
separation to which ink is applied.
The illustrated DOP printing system is a rotary DOP printing system, i.e.
the plate cylinder 10, the blanket cylinder 12 and the impression cylinder 14
rotate
during their operation in the direction indicated by the arrows 40, 42 and 44,
respectively.
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The operation of the DOP printing system 1 is controlled by a control
system 50, typically a commercially available computer equipped with dedicated
applications and cards for driving, in coordination, the elements of the
system 1.
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SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved computer
to press printing system.
According to one aspect of the present invention, there is provided a
printing system capable of printing on substrates of different formats (i.e.
different
sizes of the printing substrate) while employing the entire area of the
printing plates
mounted on the plate cylinders.
According to a preferred embodiment of the present invention, there is
provided a printing system capable of printing on printing substrates which
are both
in the B2 format and in the B3 format.
In accordance with a preferred embodiment of the present invention, the
computer to press printing system is a digital offset press (DOP) printing
system.
According to a preferred embodiment of the present invention, the DOP
printing system includes a multibeam imaging system for recording color
separations
of the artwork to be printed on at least one printing member mounted on the
plate
cylinder of the DOP printing system.
A particular feature of the DOP printing system of the present invention
is that it overcomes the misregistration between color separations of
different color
separations associated with rotary DOP printing systems employing multibeam
imaging.
In accordance with a preferred embodiment of the present invention, the
digital information of each color separation to be recorded by the multibeam
imaging
system is stored in an offset with respect to other color separations so as to
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compensate for the shift inherent to the movement of the imaging system with
respect
to the plate cylinder.
According to an alternative embodiment of the present invention, the
multibeam imaging head is capable of multi directional movement so as to
compensate for the shift of the imaging system with respect to the plate
cylinder.
According to a preferred embodiment of the present invention, the
printing members are driographic, waterless, infra red (IR) laser ablateable
printing
plates and accordingly, the imaging system includes IR lasers for emitting
radiation
capable of ablating the printing members.
According to another aspect of the present invention, the printing system
includes more than four inking assemblies for applying ink on the color
separations
produced on the printing members by the multibeam imaging system.
According to yet another aspect of the present invention, the DOP
printing system is a duplex printing system.
According to a further aspect of the present invention, the DOP printing
system includes an ink-jet printing system which operates to print customized
information on the artwork to be printed by the DOP printing system.
The present invention provides a system which is particular
advantageous for short run printing since it is characterized by a short make
ready
time, its imaging rate is relatively high since it employs a multibeam imaging
system,
it allows duplex printing and enables to record customized information on the
printed
outwork.
There is thus provided, in accordance with a preferred embodiment of
the present invention, a computer to press printing system which includes a
plate
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cylinder capable of carrying at least one printing member, an imaging system
for
recording at least one color separation on the at least one printing member,
at least
one inking assembly for applying at least one printing ink on a corresponding
one of
the at least one color separation, at least two impression cylinders each of
which for
impressing a printing substrate of a different size and a control system for
selectively
activating one of the at least two impression cylinders in accordance with the
size of
the printing substrate to be printed.
Further, according to a preferred embodiment of the present invention,
the imaging system is a multibeam imaging system.
According to one preferred embodiment of the present invention, the
multibeam imaging system operates to record at least two color separations on
the
at least one printing plate.
Still further, according to a preferred embodiment of the present
invention, the control system activates a correction to the misregistration
between the
is at least two color separations.
There is also provided, in accordance with a preferred embodiment of
the present invention, a computer to press printing system which includes a
plate
cylinder capable of carrying at least one printing member, a multibeam imaging
system for recording at least two color separations on the at least one
printing
member, at least one inking assembly for applying at least two printing inks
on
corresponding ones of the at least two color separations, an impression
cylinder, and
a control system for activating a correction to the misregistration between
the at least
two color separations.
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Further, according to a preferred embodiment of the present invention,
the correction includes shifting the data files representing the at least two
color
separations therebetween, whereby similar locations on the at least two color
separations are disposed on similar imaginary lines circumfering the plate
cylinder, the
imaginary lines being generally perpendicular to the axis of rotation of the
plate
cylinder.
According to an alternative preferred embodiment, the correction
includes translating the multibeam imaging system in a counter direction to
the axial
direction of an imaginary spiral formed by the recording lines thereof,
thereby similar
locations on the at least two color separations are disposed on similar lines
of the
plate cylinder, the lines being generally perpendicular to the axis of
rotation of the
plate cylinder.
Further, in accordance with a preferred embodiment of the present
invention, the system may also include at least one additional impression
cylinder for
impressing a printing substrate of a different size and wherein the control
system
operates to selectively activate a selected impression cylinder in accordance
with the
size of the printing substrate to be printed.
Additionally, according to a preferred embodiment of the present
invention, the system may also include a blanket cylinder disposed and acting
between the plate cylinder and the selected one of the at least two impression
cylinders whereby the system operates as an offset press.
Further, according to a preferred embodiment of the present invention,
the system may also include a conveying system for conveying to one of the at
least
two impression cylinders the printing substrate having the size corresponding
thereto.
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According to a preferred embodiment of the present invention, the
conveying system operates to flip the printed substrate and to convey it again
for
printing the second side thereof.
Additionally, in accordance with a preferred embodiment of the present
invention, the system may also include an additional printing unit for
printing
customized information on the printing substrate printed by the computer to
press
printing system.
According to a preferred embodiment of the present invention, the
printing unit is an ink-jet printing unit which operates to print the
customized
information while the printing substrate is disposed on the conveying system.
There is also provided, in accordance with a preferred embodiment of
the present invention, a method for operating a computer to press printing
system
which includes a plate cylinder capable of carrying at least one printing
member, an
imaging system for recording at least one color separation on the at least one
printing
ls member, at least one inking assembly for applying at least one printing ink
on a
corresponding one of the at least one color separation and at least two
impression
cylinders each of which for impressing a printing substrate of a different
size, the
method includes the step of activating one of the at least two impression
cylinders in
accordance with the size of the printing substrate to be printed.
Further, according to a preferred method of the present invention, the
imaging system which includes a multibeam imaging system and wherein the
method
also includes recording at least two color separations on the at least one
printing
plate.
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Additionally, according to a preferred embodiment of the present
invention, the method may also include the step of providing a correction to
the
misregistration between the at least two color separations.
There is also provided, according to a preferred embodiment of the
present invention, a method for operating a computer to press printing system
which
includes a plate cylinder capable of carrying at least one printing member, a
multibeam imaging system for recording at least two color separations on the
at least
one printing member, at least one inking assembly for applying at least two
printing
inks on corresponding ones of the at least two color separations and an
impression
cylinder, the method includes the step of activating a correction to the
misregistration
between the at least two color separations.
According to a preferred embodiment of the present invention, the
method may also include the step of providing at least one additional
impression
cylinder for impressing a printing substrate of a different size and
selectively activating
a selected impression cylinder in accordance with the size of the printing
substrate to
be printed.
According to a preferred embodiment of the present invention, the
correction may be provided by shifting the data files representing the at
least two color
separations therebetween whereby similar locations on the at least two color
separations are disposed on similar imaginary lines circumfering the plate
cylinder, the
imaginary lines being generally perpendicular to the axis of rotation of the
plate
cylinder.
Alternatively, according to a preferred embodiment of the present
invention, the correction may be provided by translating the multibeam imaging
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system in a counter direction to the axial direction of an imaginary spiral
formed by
the recording lines thereof, thereby similar locations on the at least two
color
separations are disposed on similar lines of the plate cylinder, the lines
being
generally perpendicular to the axis of rotation of the plate cylinder.
Additionally, according to a preferred embodiment of the present
invention, the method may also include the step of providing a blanket
cylinder
disposed and acting between the plate cylinder and the selected one of the at
least
two impression cylinders.
Further, according to a preferred embodiment of the present inverition,
io the method may include the step of conveying to one of the at least two
impression
cylinders the printing substrate having the size corresponding thereto and may
also
include the step of flipping the printed substrate and conveying it again for
printing the
second side thereof.
Finally, in accordance with a preferred embodiment of the present
invention, the method may also include the step of employing an additional
printing
unit for printing customized information on the printing substrate.
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BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully from
the following detailed description taken in conjunction with the appended
drawings in
which:
Fig. 1 is a schematic cross section illustration of a prior art computer to
press printing system.
Figs. 2A and 2B are schematic cross section illustrations of a computer
to press printing system, constructed and operative in accordance with a
preferred
embodiment of the present invention in first and second operation modes;
Figs. 3A - 3B and 4A - 4B are schematic cross section illustrations of the
printing system of Figs. 2A - 2B with a printing substrate feeding system, in
the first
and second operation modes, respectively.
Figs. 5A and 5B are schematic illustrations of a configuration of the four
color separations on the plate cylinder and of the corresponding alignment of
the data
representing them in the memory of the control system of the printing system
of Figs.
2A - 4B according to one preferred embodiment of the present invention;
Figs. 6A and 6B are schematic illustrations of the configuration of the
four color separations on the plate cylinder and of the corresponding
alignment of the
data representing them in the memory of the control system of the printing
system of
Figs. 2A - 4B according to another preferred embodiment of the present
invention;
and
Figs. 7A and 7B are a schematic partial top view illustration of the
imaging system and the plate cylinder of the printing system of Figs. 2A - 4B
and of
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the configuration of the four color separations on the plate cylinder
resulting from
employing the imaging system of Fig. 6A.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
Reference is now made to Figs. 2A and 2B which are schematic cross
sections of a computer to press printing system, constructed and operative in
accordance with a preferred embodiment of the present invention.
In the illustrated embodiment, the computer to press printing system is
a rotary digital offset press (DOP) printing system, generally referenced 100.
It will
be appreciated that while the present invention is described with reference to
a DOP
printing system, it is applicable to any computer to press printing system,
such as a
computer to press gravure printing system, mutatis mutandis.
One particular feature of the DOP printing system 100 is that unlike prior
art computer to press printing systems, it is capable to print on printing
substrates of
more than one size, such as on B3 size paper and B2 size paper by switching
1.5 between two modes of operation, a first one for printing B3 size paper and
a second
one for printing B2 size paper.
It will be appreciated that while the present invention is described with
respect to paper as the printing substrate, the printing substrate may be any
suitable
printing substrate, such as plastic.
The DOP printing system 100 preferably comprises a plate cylinder 102,
capable of carrying on its outer periphery two printing members 112 and 114, a
blanket cylinder 104 and at least two impression cylinders. In the illustrated
embodiment, two impression cylinders referenced 106 and 108 are shown for
printing
on B3 size paper and on B2 size paper, respectively.
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The DOP printing system 100 preferably also comprises an imaging
system 110 for recording color separations of the artwork to be printed by the
DOP
printing system 100 on the printing plates 112 and 114.
The printing plates may be any suitable printing members. Preferably,
but not necessarily, the printing plates 112 and 114 are waterless driographic
IR
ablateable printing members, such as the one described in U.S. Patent
3,535,705 to
Lewis et al.
It is a particular feature of the present invention that the imaging system
110 is a multibeam imaging system as described in detail hereinbelow.
It is another particular feature of the present invention that the number
of the color separations recorded on each of the printing plates varies in
accordance
with the size format of the printed substrate.
The DOP printing system 100 preferably also includes more than four
inking assemblies of which five inking assemblies, 116, 118, 120, 122 and 124
are
shown. Each of the inking assemblies apply ink of a different color on a
corresponding color separation.
Preferably, each one of the four inking assemblies 116, 118, 120 and
122 applies ink of one of the four process colors Cyan, Magenta, Yellow and
Black
(CMYB or CMYK) on a corresponding color separation, the general position of
which
is denoted by the letters C, M, Y and K, and the additional inking assembly
124
applies ink of one or more special colors, such as gold, on a corresponding
color
separation.
The inking stations move towards the plate cylinder 112 and away
therefrom as indicated by arrow 126 according to the current color separation
on
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which ink is applied. It will be appreciated that the number of inking
assemblies is not
limited to five inking assemblies and that the DOP printing system 100 may
include
any desired number of inking assemblies.
The DOP system 100 preferably also includes a control system,
indicated schematically by reference numeral 109. The control system 109 may
be
any suitable computer, such as an International Business Machine (IBM)
personal
having a CPU, such as the Intel 40486, a storage system, such as a hard disk
and
any suitable control application and control cards for driving and
coordinating the
operation of the elements of the DOP system 100.
As is known to the ordinary person skilled in the art, in prior art computer
to press printing systems, each color separation of the artwork to be printed
is
recorded on a separate printing member. In the present invention, in each
operation
mode, the number of color separations recorded on each printing member is
different.
In the illustrated embodiment, the DOP printing system 100 includes two
modes of operation in accordance with the paper size on which the artwork is
to be
printed.
In its first mode of operation (Fig. 2A), the DOP printing system 100 is
operative to print a desired artwork on an B3 size paper 107. For the B3 paper
which
is smaller than B2 paper, the corresponding impression cylinder is impression
cylinder
106 which is illustrated in a working position, impressing the B3 size paper
107
against the blanket cylinder 104.
In the DOP printing system 100, an artwork to be printed on B3 size
paper 107 is preferably printed in a single pass. The term pass refers herein
to a
cycle of imaging, application of ink, color transfer and impression on the
paper.
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For an B3 size paper 107, provided that no special colors, i.e. colors
other than the four color separations are printed, the imaging system 110
records
each two of the four color separations of the four process colors on the two
printing
members 112 and 114, the four inking assemblies 116, 118, 120 and 122 apply a
corresponding ink on each one of the color separations and the blanket
cylinder
operates to transfer each one of the colors to the paper 107 impressed by the
impression cylinder 102.
It will be appreciated that each color separation is recorded on a
different half of one of the printing members 112 and 114 so as to provide the
four
process color separations CMYK.
It will be appreciated that if a special color is to be used, such as gold,
the printing members 112 and 114 are replaced by new printing members 112 and
114 and a second pass of imaging, ink application and color transfer and
impression
takes place.
In its second mode of operation (Fig. 2B) the DOP printing system 100
operates to print on the larger size B2 paper 109 and accordingly the
impression
cylinder 108 is in a working position.
For printing on the B2 size paper, two passes are required if the artwork
to be printed includes the four process colors and more if special colors are
required.
In the first pass, two color separations, for example that of cyan and
magenta which are schematically indicated by the letters C and M, are recorded
on
the printing members 112 and 114. Then, two inking assemblies 116 and 120
apply
corresponding ink on the printing members 112 and 114, respectively, and the
inks
are subsequently being transferred to the B2 size paper.
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The printing members 112 and 114 are replaced with new ones and in
a second pass the yellow and black color separations are recorded on the
members
112 and 114, respectively. Then, the inking assemblies 118 and 120 apply
yellow
and black inks on the members 112 and 114, respectively, and the ink is
transferred
to the B2 size paper 109 to complete the printing of the artwork.
It will be appreciated that the size of the printing members 112 and 114
is selected to correspond to the size of the color separation of the largest
paper to be
printed. In the illustrated embodiment, B2 paper is the largest paper to be
printed and
therefore, the plate cylinder 102 includes on its outer periphery two printing
members
112 and 114. However, if one desires that the DOP printing system 100 will
print on
a larger size paper than B2, it may include only one printing member around
its
periphery on which one color separation is recorded.
Reference is now made to Figs. 3A - 3B and 4A - 4B which are
schematic cross sections of the printing system of Figs. 2A - 2B with a
printing
1s substrate feeding system, generally referenced 130, in the first and second
operation
modes, respectively.
Figs. 3A - 3B correspond to the B3 operation mode illustrated in Fig. 2A
and Figs. 4A and 4B correspond to the B2 operation mode illustrated in Fig.
2B.
The feeding system 130 feeds the paper to the DOP printing system 100
and may flip it after the first side thereof has been printed so as to enable
duplex
printing.
The feeding system 130 preferably comprises three movable paper trays
referenced 132, 134 and 136 and three movable conveyers, each of which
includes
a conveying belt turned in a capstan fashion by two wheels. The belt of the
three
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conveyers are referenced 140, 141 and 142 and their wheels 240, 240', 241,
241' and
242 and 242', respectively.
The trays 132, 134 and 136 preferably move along a generally vertical
direction by any suitable means such as motor means (not shown) so they can be
used for duplex printing as described in detail hereinbelow. The trays 132,
134 and
136 store any paper size to be printed by the DOP system 100.
In addition to the capstan fashion turnaround movement of the
conveyers belts 140, 141 and 142, the conveyer belts 140 and 141 are
preferably
capable of pivotal movement wherein the wheels 240 and 241 are fixed and the
wheels 240' and 241' are movable so as to direct the conveyer belts to either
of the
conveying systems 144 and 146 as described hereinbelow.
Fig. 3A illustrates the working position of the trays and conveyers for the
first side of printing of the B3 size paper 107. In this working position
paper is
conveyed from the tray 136 on the upper side of conveyer belt 140 and the
bottom
side of conveying system 144 of the DOP system 100 to its position between the
blanket cylinder 104 and the impression cylinder 106 and after printing
thereof, it is
conveyed on the upper side of the conveying system 144 via the upper side of
the
conveying belt 141 to the upper side of the conveying belt 142. When the
printed
sheet reaches the edge of the conveying belt 142 it falls upside down into the
tray
134.
Fig. 3B illustrates the working position of the trays and conveyers for the
second side of printing of the B3 size paper 107. In this working position
paper is
conveyed from the tray 134 via belt 140 and conveying system 144 to its
position
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between the blanket cylinder 104 and the impression cylinder 106, and after
printing
via conveyer belt 141 and 142 to the tray 132.
Similarly, Figs. 4A and 4B illustrate the working positions of the feeding
system 130 for printing the first and second sides of B2 size paper 109,
respectively.
In this embodiment the conveyer belts 140 and 141 operate to direct the paper
to the
conveying system 146 of the impression cylinder 108.
Additionally, according to a preferred embodiment of the present
invention, a suitable printing system, such as an ink jet printing system
illustrated
schematically be reference 150 and having an ink drying mechanism 149 may be
io disposed along the paper path between the DOP printing system 100 and the
paper
trays for printing customized information, such as the address of the
recipient of the
printed artwork.
It will be appreciated that the term customized information applies herein
to any information which has to be printed on part of the printed artwork of a
single
printing job. Examples are the home address of an individual, the business
address
of a number of individuals and the serial number or the series number of an
artwork.
Reference is now made to Figs. 5A - 7B which illustrate three different
embodiments of multibeam imaging of the printing members 112 and 114, i.e.
recording simultaneously more than a single line per one rotation of the plate
cylinder
102. Figs. 5A - 7B are described by way of example only with respect to B3
size
paper printing. It will be appreciated that they are applicable to printing
with any other
paper size, such as with the B2 size paper 109.
Figs. 5A, 6B and 7A are simplified schematic illustrations which illustrate
three embodiments of multibeam imaging of the DOP system 100. For illustration
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purposes only, Figs. 5A, 6A and 7B illustrate the two plates 112 and 114,
carrying the
four color separations 117, 119, 121 and 123, on the part of the plate
cylinder 102
visible in these figures. It will be appreciated that, as illustrated in any
of Figs. 2A -
4B, the plate cylinders 112 and 114 preferably occupy a larger portion of the
circumference of the plate cylinder 102 and similarly, the four color
separations 117,
119, 121 and 123 occupy generally a large portion of the plate cylinders 112
and 114.
Typically, as best seen in Fig. 7A, in the course of recording the color
separations on the printing plates 112 and 114, the cylinder 102 rotates as
indicated
by the arrow 152 about its longitudinal axis 156 while the imaging head 110
translates
io as indicated by arrow 154 so as to record the color separations on the
printing plates
112 and 114.
Since the imaging head translates during the rotation of the plate
cylinder 102, the recording lines of the imaging system form an imaginary
spiral
having an axial translation along its axis 156.
This spiral effect causes misregistration between the four color plates,
this is to say that similar points on the four color separations are not lying
on lines
perpendicular to the plate cylinder 102 and therefore, when the ink applied
thereto will
be impressed to the paper, the colors of a similar point which form together
the final
color of that point on the paper 107 will not superimpose but will have
different
locations, i.e. will be misregistered.
The spiral effect is neglected in prior art DOP printing systems employing
a single beam imaging source since the resulting shift between the color
separations
are within the limits required for registration therebetween. However, since
this effect
is multiplied when multibeam imaging is used to record the color separations,
the
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present invention provides two different solutions for the spiral effect as
described in
detail with respect to Figs. 6A - 7B.
According to a preferred embodiment of the present invention (Figs. 6A -
6B), the color separations are recorded in a spiral like fashion but are
shifted
therebetween as described in detail hereinbelow so as to provide adequate
registration therebetween.
According to an alternative preferred embodiment of the present
invention (Figs. 7A - 7B), the registration between the images is provided by
recording
all the color separations of the image on the plate cylinder generally
perpendicular to
its rotation axis 156 so as to avoid spiral like recording which result in
misregistration
between the color separations of the artwork to be printed by the DOP printing
system
100.
It will be appreciated that according to a preferred embodiment of the
present invention, the operator selects whether the DOP system 100 will
operate
i5 without a correction to the spiral effect (Figs. 5A - 5B) or with either of
the corrections
of Figs. 6A - 6B or Figs. 7A - 7B or in a desired combination therebetween.
Fig. 5A illustrates the result of using multibeam imaging without providing
a correction to the spiral recording effect. In the three illustrated
embodiments, the
imaging system 110 images four beams 170A, 170B, 170C and 170D (Fig. 7A) on
the
printing plate 112. It will be appreciated that this is by way of example only
and that
the imaging system 100 may include any desired number of light beams imaged on
the printing plates of the DOP system 100.
As seen in Fig. 5A, the edges of each of the color separations 117, 119,
121 and 123, referenced respectively 317, 319, 321 and 323 are along the
imaging
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line 252 and so will be any other corresponding points of the color
separations 117,
119, 121 and 123. The imaging line 252 as well as any other imaging line, such
as
the line 262, are diagonal to a line 250 perpendicular to the axis 156 of the
plates
cylinder 112 and 114. Therefore, the color separations are recorded in a
misregistration therebetween.
Fig. 5B illustrates the corresponding alignment of the four data files
corresponding to the four color separations 117, 119, 121 and 123 and
referenced
respectively, 217, 219, 221 and 223, in the memory of the control system 109.
Since
in the embodiment of Figs. 5A and 5B no correction to the spiral effect is
required by
the operator of the DOP system 100, the data files 217, 219, 221 and 223 are
aligned
and are not shifted therebetween.
Figs. 6A and 6B illustrate the result of using multibeam imaging when
a correction to the spiral effect is provided by shifting the data files 217,
219, 221 and
223 with respect to each other in the memory of the control system 109 (Fig.
6B).
The resulting imaging lines from a single rotation of the drum cylinder
are referenced 252, 254, 256, 258. It will be appreciated that while the
recording
lines are diagonal with respect to the line 250 which is perpendicular to the
axis 156,
the edge of each of the color separations 117, 119, 121 and 123, referenced
317,
319, 321 and 323, respectively, are along an imaginary line which is also
perpendicular to the axis 156. Therefore, the points 317, 319, 321 and 323 are
registered and the color applied thereto will superimpose on the paper 107.
However, since color separations 117, 119, 121 and 123 are diagonal
with respect to line 250, i.e. are rotated with respect to the edges of
cylinder 102, the
resulting printed image will not be parallel to the edges of paper 107 if, as
is usually
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the case, paper 107 is fed in parallel to the cylinders 102 and 104 edges.
Therefore,
if the printed image is to be parallel to the edges of paper 107, the paper is
fed with
a corresponding rotation to that of color separations 117, 119, 121 and 123.
It will be appreciated that, similarly, any other point on the color
separations are lying as a result of the correction on the same imaginary line
perpendicular to the axis 156 and therefore the separations are in
registration
therebetween.
It will be appreciated that the distance between the recording lines 252,
254, 256 and 258 is equal to the spacing between the beams 170A, 170B, 170C
and
170D of the imaging system 110. Similarly, the lines resulting from a
subsequent
rotation of the plate cylinder 112 of which only one, line 262 is shown, are
evenly
spaced and correspond to the spacing between the beams 170A - 170D generated
by the imaging system 110.
It is a particular feature of the present invention that the shift between
is the data files 217, 219, 221 and 223 in the memory of the control system
109 also
corresponds to the spacing between the beams 170A - 170D generated by imaging
system 110.
The embodiment illustrated in Figs. 7A and 7B illustrates the recording
of the color separations of the image generally perpendicular to the rotation
axis 156.
This is achieved by compensating for the movement of the imaging system with
respect to the plate cylinder with a counter movement thereof as described in
detail
hereinbelow.
As shown in Fig. 7A, the imaging system 110 comprises a guiding
support 160 and an imaging optical assembly 162.
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The optical imaging assembly 162 preferably comprises a plurality of IR
laser diodes, collectively referenced 164, and of which four laser diodes
164A, 164B,
164C and 164D are illustrated for exemplary purposes in the illustrated
embodiment,
and four light guides which are preferably, but not necessarily fiber optics
collectively
referenced 166 and of which four, 166A, 166B, 166C and 166D collect the light
from
each of the IR laser diodes 164, respectively.
The ends of the fiber optics 166 are bundled to provide a linear array
multi beam light source 168, the four light beams 168A, 168B, 168C and 168D
are
imaged by lens 170 on the printing plate 112 as light beams 170A, 170B, 170C
and
170D.
A particular feature of the imaging system 110 is that it is capable of two
simultaneous movements, one is the movement of the optical assembly 162 along
the
support 160 as indicated by arrow 154, and the other being the movement of the
multibeam light source 168 along a second support 172 as indicated by arrows
174.
The resulting imaging lines of which only one, referenced 252, is shown
in Fig. 7B for simplicity, are all parallel to the line 250 and perpendicular
to the axis
156 and provide registration therebetween and therefore misregistration
between
similar points on the four color separations is avoided.
It will be appreciated that the control system 109 activates one of the
corrections described above either in response to an input from the operator
or in
accordance with predetermined definitions which associate different printing
applications with different corrections. For example, the system may be
defined as
providing the correction of the embodiment of Figs. 7A - 7B when high quality
brochures are to be printed by the system 100 whereas no correction is
required
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when law quality publication is printed. In the second mode, the operator
selects the
type of printing application and the desired paper size and the control system
activates the corresponding impression cylinder and if required, the
appropriate
correction.
It will be appreciated that the preferred embodiments described
hereinabove are described by way of example only and that numerous
modifications
thereto, all of which fall within the scope of the present invention, exist.
For example,
four color separations may be recorded on each of the printing members 112 and
114
so as to enable use of smaller size paper.
Another example is that while the present invention has been described
hereinabove with respect to paper as the printing substrate, the DOP printing
system
100 may operate to print on any suitable printing substrate, such as plastic.
It will be appreciated by persons skilled in the art that the present
invention is not limited to what has been particularly shown and described
hereinabove. Rather, the scope of the present invention is defined only by the
claims
that follow:
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