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Claims  |
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What is claimed as new and desired to be secured by Letters Patent of the
U.S. is:
1. Printing apparatus comprising a machine frame; a large diameter
impression cylinder rotatably mounted to the frame; a plurality of print
stations spaced around the impression cylinder, each said print station
including a blanket cylinder rotatively mounted to the frame and in
rolling contact with said impression cylinder and a plate cylinder
rotatably mounted to the frame and in rolling contact with said blanket
cylinder, the diameters of all of said plate and blanket cylinders being
substantially the same and said impression cylinder having a diameter that
is equal to or larger than the product of the plate cylinder diameter
multiplied by an integer, and each cylinder including a correspondingly
sized circular gear fixed coaxially to rotate with that cylinder, the
blanket cylinder gear of each print station meshing with both the plate
cylinder gear and the impression cylinder gear at that station, said
impression cylinder gear being composed of a plurality of arcuate gear
segments whose arc lengths are equal to the circumferences of the plate
and blanket cylinder gears, the corresponding teeth of all of said
impression cylinder gear segments having tooth profiles which are
substantially indentical having been cut in parallel simultaneously by the
same gear cutting tool so that gearing errors are periodic around the
impression cylinder gear.
2. The printing apparatus defined in claim 1 wherein the impression
cylinder diameter is an integer multiple of the plate cylinder diameter.
3. The printing apparatus defined in claim 2 wherein said integer is four
or more and said rotating means rotates said impression cylinder.
4. The printing apparatus defined in claim 1 wherein the number of gear
segments is the same as or an integer number more than the number of print
stations.
5. The printing apparatus defined in claim 1 and further including means on
the impression cylinder for releasably gripping the leading edge of a
sheet, said gripping means being movable between gripping and releasing
positions; means for feeding sheets one-by-one to said impression cylinder
for gripping by the gripping means when the latter are in their releasing
position; means for stripping each sheet from the impression cylinder when
said gripping means are in their releasing position, and means for moving
the gripping means between said two positions so that the gripping means
are in their releasing position only over a relatively small selected
sector of the angular motion of the impression cylinder that is not
disposed opposite a print station whereby each fed sheet, upon being
gripped by said gripping means, is wrapped about the impression cylinder
and advanced past all of said print stations before being stripped from
the impression cylinder by said stripping means.
6. The printing apparatus defined in claim 5 wherein said impression
cylinder carries a plurality of said gripping means spaced around its
circumference, the number of same being at least equal to the number of
print stations in the press.
7. The printing apparatus defined in claim 6 wherein the number of gripping
means is equal to the number of times that the impression cylinder
diameter is longer than the plate cylinder diameter.
8. The printing apparatus defined in claim 1 wherein each print station
also includes image receiving means on the surface of the plate cylinder
thereat, and means for applying an image to the image receiving means at
that station and further including means for receiving color separated
electronic image signals representing the different color components of an
original document and control means responsive to said signals for
controlling the imaging means at each print station so that they apply a
color separated image to the image receiving means on the plate cylinder
at that station.
9. The printing apparatus defined in claim 8 wherein each said imaging
means comprise a scanning energy source selected from the group consisting
of laser, spark electrode and light emitter.
10. The printing apparatus defined in claim 8 wherein said control means
process said signals to position each image on an image receiving means so
as to compensate for said gearing errors that affect the angular position
of each of said plate cylinders with respect to the impression cylinder.
11. The printing apparatus defined in claim 1 wherein each print station
also includes an ink system for applying ink to said plate cylinder
thereat, said ink system including means responsive to control signals for
regulating the amount of ink applied to the corresponding plate cylinder
along its length, and control means for providing control signals to said
regulating means at each print station, said control means counting the
number of image dots to be formed by each print station on selected
portions of said plate cylinder and controlling said ink system for that
print station based on the number of dots to be printed by that print
station on said plate cylinder portions.
12. The printing apparatus defined in claim 11 and further including color
densitomiter means for sensing colors in the printed matter printed by the
printing apparatus, means for comparing the densitomiter means readings
with the dot count for each print station to produce a color correction
signal and means for applying said correction signal to said control means
to readjust the number of dots to be printed by that station on said plate
cylinder portions.
13. Printing apparatus comprising a machine frame; a relatively large
diameter first cylinder rotatably mounted to the frame; a circular gear
coaxially fixed to said first cylinder, said gear having a diameter that
is substantially the same as that of the first cylinder and being composed
of a plurality of separate arcuate segments, the corresponding teeth of
all of said gear segments having substantially identical tooth profiles
having been cut in parallel simultaneously by the same gear cutting tool,
each said gear segment defining a printing sector of said first cylinder;
a plurality of substantially identical second cylinders rotatably mounted
to said frame in rolling contact with said first cylinder at spaced-apart
locations around the first cylinder; a corresponding plurality of second
cylinder gears coaxially fixed to said second cylinders, said second
cylinder gears having the same diameter as said second cylinders and being
in mesh with said circular gear, the arc length of each of said circular
gear segments being equal to the circumferences of said second cylinder
gears.
14. The printing apparatus defined in claim 13 wherein the number of gear
segments is the same as or an integer number greater than the number of
second cylinders.
15. The printing apparatus defined in claim 13 and further including a
third cylinder rotatably mounted to said frame in rolling contact with a
unique one of said second cylinders; a third gear coaxially fixed to each
of said third cylinders, each said third gear having the same diameter as
and being in mesh with, the second cylinder gears; means for rotating said
first cylinder gear; imaging means movably positioned adjacent to each of
said third cylinders to scan a raster on the surface of the corresponding
third cylinder, and means for actuating each imaging means in response to
color separated electronic image signals at selected points in the scan of
said imaging means to apply a color separated image in the form of dots to
the surface of the corresponding third cylinder.
16. The printing apparatus defined in claim 15 and further including means
on the impression cylinder for releasably gripping the leading edge of a
sheet, the number of gripping means being equal to the number of times
that the impression cylinder diameter is longer than the plate cylinder
diameter and each gripping means being movable between gripping and
releasing positions.
17. The printing apparatus as defined in claim 15 and further including
means for controlling the actuating means so as to compensate
electronically for cyclical errors in the placements on copies of the half
tone color dots printed by said printing apparatus.
18. Printing apparatus comprising a frame; a relatively large diameter
first cylinder rotatably mounted to said frame; a first circular gear
coaxially fixed to said first cylinder for rotation therewith, said first
gear having essentially the same diameter as said first cylinder and being
composed of a plurality of separate arcuate sectors the corresponding
teeth of all of said sectors having identical tooth profiles having been
cut in parallel simultaneously by the same gear cutting tool; at least one
second cylinder rotatably mounted to said frame in rolling engagement with
said first cylinder; at least one second circular gear coaxially fixed to
said at least one second cylinder for rotation therewith, said at least
one second gear having the same diameter as said at least one second
cylinder and being in mesh with said at least one first gear; at least one
imagable third cylinder rotatably mounted to said frame, said at least one
imagable third cylinder having the same diameter as, and being in rolling
engagement with, said at least one second cylinder and at least one third
circular gear coaxially fixed to said at least one third cylinder for
rotation therewith, said at least one third gear having the same diameter
as, and being in mesh with, said at least one second gear, the arc length
each of said first gear sectors being equal to the circumference of each
of said at least one second and third gears.
19. The printing apparatus defined in claim 18 wherein there are a
plurality of corresponding second and third cylinder and gear sets
comprising separate print stations spaced around said first cylinder, the
number of first gear segments being equal to or exceeding the number of
print stations, each print station also includes an ink system for
applying ink to said plate cylinder thereat, said ink system including
means responsive to control signals for regulating the amount of ink
applied to the corresponding plate cylinder along its length, and control
means for providing control signals to said regulating means at each print
station.
20. The printing apparatus defined in claim 18 and further including means
for applying ink to the surface of each third cylinder and means
responsive to ink control signals for adjusting each applying means to
regulate the distribution of ink along each third cylinder, and control
means for providing said ink control signals to each said adjusting means,
said control means counting the number of image dots to be formed by each
print station on selected portions of said third cylinder and controlling
said adjusting means for that print station based on the number of dots to
be printed by that print station on said third cylinder portions.
21. The printing apparatus defined in claim 20 and further including color
densitomiter means for sensing colors in the printed matter printed by the
printing apparatus, means for comparing the densitomiter means readings
with the dot count for each print station to produce a color correction
signal and means for applying said correction signal to said control means
to readjust the number of dots to be printed by that station on said third
cylinder portions.
22. The printing apparatus defined in claim 18 and further including means
on said first cylinder for releasably gripping the leading edge of a
sheet, the number of gripping means being equal to the number of times
that said first cylinder diameter is longer than the plate cylinder
diameter and each gripping means being movable between gripping and
releasing positions.
23. The printing apparatus defined in claim 18 and further including
imaging means responsive to image signals and positioned opposite each
third cylinder for applying images thereto and control means for applying
image signals to each said imaging means, said control means including a
computerized work station for receiving and processing picture signals to
develop said image signals.
24. Printing apparatus comprising
a machine frame;
an impression cylinder rotatably mounted to the frame;
at least one print station positioned opposite the impression cylinder,
each print station including a blanket cylinder rotatably mounted to the
frame for rolling contact with the impression cylinder, a plate cylinder
rotatably mounted to the frame for rolling contact with the blanket
cylinder and means for applying image dots to a plate supported by the
plate cylinder;
means for rotating said cylinders in unison;
means for applying ink to said plate;
ink regulating means responsive to ink control signals for regulating the
amount of ink applied to the plate by the ink applying means at each print
station; and
control means responsive to picture signals for actuating the image
applying means at each print station to form on said plate a corresponding
image comprised of dots, said control means counting the number of image
dots to be formed by each print station on selected portions of said plate
and controlling the ink regulating means for that print station based on
the number of dots to be printed by that print station on said plate
portions.
25. The printing apparatus defined in claim 24 and further including color
densitomiter means for sensing colors in the printed matter printed by the
printing apparatus, means for comparing the densitomiter means readings
with the dot count for each print station to produce a color correction
signal and means for applying said correction signal to said control means
to readjust the number of dots to be printed by that station on said plate
portions.
26. Printing apparatus comprising
a machine frame;
an impression cylinder rotatably mounted to the frame;
at least one print station positioned opposite the impression cylinder,
each print station including equal diameter plate and blanket cylinders,
rotatably mounted to said frame parallel to the impression cylinder and
means for imaging a plate supported on the plate cylinder, said cylinders
having correspondingly sized coaxial meshing gears for rotating said
cylinders in unison, said impression cylinder gear being composed of a
number of arcuate segments corresponding to the number of print stations,
the arcuate length of each gear segment being equal to the circumferences
of said plate and blanket cylinder; and
means for rotating said cylinders.
27. Printing apparatus comprising
a machine frame;
an impression cylinder rotatably mounted to the frame;
at least one print station positioned opposite the impression cylinder,
each print station including equal diameter plate and blanket cylinders
rotatably mounted to said frame parallel to the impression cylinder and
means for imaging a plate supported on the plate cylinder, said cylinders
having correspondingly sized coaxial meshing gears for rotating said
cylinders in unison, said impression cylinder gear being composed of a
number of arcuate segments corresponding to the number of print stations,
the arcuate length of each gear segment being equal to the circumferences
of said plate and blanket cylinder gears and said gear segments having
corresponding teeth with substantially identical tooth profiles those
teeth having been cut in parallel simultaneously by the same gear cutting
tool; and
means for rotating said cylinders.
28. Printing apparatus comprising
a machine frame;
an impression cylinder rotatably mounted to the frame;
at least one print station positioned opposite the impression cylinder,
each print station including equal diameter plate and blanket cylinders
rotatably mounted to said frame parallel to the impression cylinder and
means for imaging a plate supported on the plate cylinder, said cylinders
having correspondingly sized coaxial meshing gears for rotating said
cylinders in unison, said impression cylinder gear being composed of a
number of arcuate segements corresponding to the number of print stations,
the corresponding teeth of said gear segments having substantially
identical tooth profiles having been cut in parallel simultaneously by the
same gear cutting tool. |
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Claims |
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Description |
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This invention relates to printing method and means. It relates more
particularly to improved apparatus for printing high quality copies in
color and to the printing method carried out by that apparatus.
BACKGROUND OF THE INVENTION
There are a variety of known ways to print hard copy. To name a few, the
traditional techniques include rotogravure printing and offset
lithography. Both of these printing methods require a plate which bears an
image of the original document or picture to be copied and usually the
plate is loaded onto a plate cylinder of a rotary press so that copies can
be made efficiently. In the case of gravure printing, the plate cylinder
is inked and the inked image thereon is impressed directly onto the paper
or other copying medium. In the case of lithography, the image is present
on a plate or mat as hydrophyllic and hydrophobic surface areas. Water
tends to adhere to the water-receptive or hydrophyllic areas of the plate
creating a thin film of water there which does not accept ink. The ink
adheres to the hydrophobic areas of the plate. Those inked areas, usually
corresponding to the printed areas of the original document (direct
printing), are transferred to a relatively soft blanket cylinder and that,
in turn, applies the image to the paper or other copying medium brought
into contact with the surface of the blanket cylinder by an impression
cylinder.
While certain aspects of the present invention are applicable to both kinds
of printing and the approach can be applied to any number of colors
including one as will be pointed out in more detail later, we will
describe the invention in the context of a sheet-fed four-color offset
press.
The plates for an offset press are usually produced photographically. In a
typical negative-working subtractive process, the original document is
photographed to produce a photographic negative. The negative is placed on
an aluminum plate having a water-receptive oxide surface that is coated
with a photopolymer. Upon being exposed to light through the negative, the
areas of the coating that received light (corresponding to the dark or
printed areas of the original) cures to a durable oleophyllic or
ink-receptive state. The plate is then subjected to a developing process
which removes the noncured areas of the coating that did not receive light
(corresponding to the light or background areas of the original) and these
non-cured areas become hydrophyllic (water loving). The resultant plate
now carries a positive or direct image of the original document.
If a press is to print in more than one color, a separate printing plate
corresponding to each color is required, each of which is usually made
photographically as just described. In addition to preparing the
appropriate plates for the different colors, the plates must be mounted
properly on the plate cylinders in the press and the positions of the
cylinders coordinated so that the color components printed by the
different cylinders will be in register on the printed copies.
In most conventional presses, the printing stations required to print the
different colors are arranged in a straight line or flatbed approach. Each
such station contains all of the elements required to print a single
color, including an impression cylinder, a blanket cylinder, a plate
cylinder and the necessary ink and water systems for applying ink and
water to the plate cylinder. The equaldiameter plate and blanket cylinders
at each station are geared to the impression cylinder there and the latter
is geared to the impression cylinders in the other stations so that all of
the press cylinders rotate in unison to maintain registration of the
different color components of each copy.
To make a copy on that type of press, a sheet of paper is fed to the first
print station where its leading edge is gripped and the sheet wrapped
around the impression cylinder at that station. The press then operates to
print onto the sheet, say, the cyan color component of the original
document being copied, after which that sheet is discharged to the second
printing station of the press. At station No. 2, the leading edge of the
sheet is picked up by a second gripper and wrapped around the impression
cylinder of that station. The press then operates to print a second, e.g.
the yellow, color component of the original document onto the paper sheet,
after which the sheet is discharged to the third printing station which
grabs the sheet and prints the third color component, i.e. magenta, onto
the sheet. In four-color printing, the sheet passes through a fourth
station which prints a black image onto the sheet. Thus, successive paper
sheets are fed into the press, are printed on at the various print
stations thereof, and then exit the press carrying a three or four-color
image of the original document or picture.
A conventional press such as the one just described has several drawbacks.
First of all, since it consists essentially of three or four single color
presses arranged one after the other, it occupies a considerable amount of
floor space. A present day four-color press of this type can be as long as
20 feet. Secondly, the sheet has to be picked up and wrapped around the
impression cylinder at each print station of the press. Thus, in a
four-color press, four separate operations are required to position the
sheet for printing. This means that each printing station must have its
own paper feeding and handling mechanisms. Not only does this increase the
cost of the press, it also introduces print registration errors into the
printed copies.
Normally in a press, misregistrations are corrected for by manually or
automatically adjusting the relative positions of the plate cylinders at
the various print stations in a proper rotational, axial, and
skew-orientation phase. It has been proposed that by imaging the plates
"on press" the time required to correct for misregistration will be
substantially decreased. The imaging of the plates can be controlled by
incoming image signals representing the original document to be copied or
reproduced in high volume. Indeed, it has been proposed to image an offset
plate on the press using an ink jetter. The ink jetter is controlled so as
to deposit on the plate surface a thermoplastic imageforming resin or
material which has a desired affinity for the printing ink being used to
print the copies.
While that proposed system may be satisfactory for some applications, it is
not always possible to provide thermoplastic image-forming material that
is suitable for jetting and also has the desired affinity (phyllic or
phobic) for the inks commonly used to make lithographic copies. Further,
ink jet printers are generally unable to produce small enough ink dots to
allow the production of smooth, continuous tones on the printed copies,
i.e. the resolution is not high enough.
In any event, such manual, automatic or electronic registration correction
procedures are not totally satisfactory for a sheet fed press because the
registration errors due to the multiple grippings of each sheet are random
errors that cannot be corrected completely by onetime adjustments of the
plate cylinders or of the images thereon. Nor are such procedures
effective to correct for misregistration due to random gearing errors
caused by variations in the tooth profiles of the meshing gears that drive
the various cylinders of the press. These tooth profile variations arise
in the process of cutting the gears and they are more noticeable in large
diameter gears.
Since such random errors are not normally correctable, press manufacturers
have had to resort to minimizing the problem by using very accurate paper
feeding mechanisms and precision gearing. Such precision parts are quite
expensive and materially increase the overall cost of the press. Also, as
alluded to above, the misregistration problem is not completely eliminated
and can still manifest itself in a press intended to print high quality,
high resolution copies, which is the type of press we are primarily
concerned with here.
Thus, although considerable effort has been devoted to improving different
aspects of printing, including lithographic printing, there still does not
exist a compact, relatively low cost printing apparatus or press whose
printing plates or cylinders can be formed right on the press using
incoming digital data representing original documents or pictures to
enable the printing in long or short runs of high quality continuous tone
color reproductions or copies. It would, therefore, be highly desirable if
such apparatus could be made available particularly as a relatively
compact sheet fed press and at a cost affordable to printers and other
businessmen who want to do high quality printing and publishing in-house.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide printing
apparatus in the nature of a press which can print economically, in both
long or short runs, high quality copies in black and white and in color.
Another object of the invention is to provide a press of this type whose
printing plates can be imaged right in the press using image signals from
any available source.
Another object of the invention is to provide an offset press which
minimizes registration errors in the copies being printed.
Still another object of the invention is to provide printing apparatus of
this type which compensates electronically and mechanically for
registration errors that are introduced into the printing process.
Yet another object of the invention is to provide a sheet fed color press
which prints in three or four colors using only a single impression
cylinder thereby reducing the need to compensate for registration errors
caused by page handoffs of the printed copies.
Still another object of the invention is to provide such printing apparatus
which achieves complete computer control over the entire printing process,
including plate generation, ink regulation and the start up, print, hold,
shut down and cleanup stages of the actual printing operation.
Yet another object of the invention is to provide a method of color
printing which minimizes registration errors in the printed impressions.
Other objects will, in part, be obvious and will, in part, appear
hereinafter.
The invention accordingly comprises the several steps in the relation of
one or more of such steps with respect to each of the others and the
apparatus embodying the features of construction, combination of elements
and arrangement of parts which are adapted to effects of steps, all as
exemplified in the following detailed description, and the scope of the
invention will be indicated in the claims.
Briefly, our printing apparatus is designed to accept electronic signals
that represent color-separated images that are to be printed. It is
implemented as a sheet-fed offset press. However, whereas prior presses of
this type comprise a series of more-or-less self-contained print stations
arranged one after another in a line, in our press, the print stations are
disposed around a single large diameter impression cylinder, there being
one station for each color. Thus, a four-color press has four offset print
stations positioned around the impression cylinder, the stations all being
similar to one another and the equal diameter plate and blanket cylinders
therein being geared directly to the impression cylinder. When the press
is operating, the paper sheets to be printed on are fed successively from
a stack to the impression cylinder as that cylinder rotates.
Circumferentially spaced clamping mechanisms on the cylinder grab
successive fed sheets on the fly so that the sheets become wrapped and
properly positioned around the impression cylinder and are advanced
successively past print stations, in turn, so that each paper sheet is
printed with a plurality of colors. The printed sheets are then stripped
successively from the impression cylinder and stacked in a conventional
manner.
To maximize the printing rate, the press is designed so that successive
paper sheets are being printed by all of the print stations
simultaneously. This means that the circumference of the impression
cylinder must be large enough so that a number of paper sheets
corresponding the number of print stations, e.g. four, can be wrapped
around the cylinder at the same time. On the assumption that the plate
cylinder at each print station is large enough to print a full-size image
on one sheet of paper, this means that the diameter of the impression
cylinder must be at least equal to the diameter of the plate cylinder
multiplied by the number of print stations. In practice, the impression
cylinder diameter can be larger than that product so that while the sheets
are being printed at the four print stations, the press can also be in the
process of loading a fresh sheet onto the impression cylinder and
stripping a fully printed sheet from that cylinder. Thus, for a four color
press, the diameter of the impression cylinder can be more than four times
larger than the plate cylinder diameter. Actually, for reasons to be
discussed presently, the two diameters should also differ by an even
multiple. Thus, in a four color press, the impression cylinder should be
exactly four, five, six, etc. times larger than the plate cylinder. In a
three color press, the multiple would be three, four, five, etc.
It can be appreciated that there is a distinct advantage to arranging all
of the print stations around a single large impression cylinder in that
each sheet being printed on is clamped to the impression cylinder only
once and is rotated past all four print stations before being released to
the delivery end of the press. Since each sheet remains clamped on the
impression cylinder during the entire printing process, there is less apt
to be registration errors due to movement or mispositioning of the sheets.
Also, the grouping of the print stations around a single impression
cylinder materially reduces the floor space required by the press. Indeed,
a press incorporating our invention requires only about one-third the
linear floor space necessary to site a conventional four color offset
press.
Each print station of our press includes equal-diameter plate and blanket
cylinders and the usual ink and water systems that apply ink and water to
the lithographic plate on the plate cylinder. Preferably, the ink system
or fountain is of the type that permits automatic ink flow adjustment. The
cylinders at all of the printing stations are geared directly to a unitary
gear on the impression cylinder so that all of the cylinders rotate in
unison. However, instead of being a unitary gear, this gear is specially
constructed of five identical arcuate sections which are assembled on the
impression cylinder to form a circular gear having essentially the same
diameter as the impression cylinder. The gear thus divides the
circumference of the impression cylinder into five arcuate printing
sectors, (one for each of the four sheets being printed on and one extra
to allow for loading and unloading sheets), each of which is equal to one
printing period, i.e. one revolution of each plate cylinder. This means
that if there are any gearing errors in the coupling of the plate and
impression cylinders, the errors will be periodic around the circumference
of the latter gear. Being non-random, those errors can now be corrected or
compensated for by adjusting the relative phases of the plate cylinders or
of the images thereon.
While the lithographic plates on the plate cylinders at the various print
stations may be conventional ones, more preferably, they are of a type
that can be imaged "on press" by imaging apparatus, e.g. lasers, at the
print stations which respond to incoming image signals representing the
respective color components of the original document or picture being
printed by the stations. Such on-press imaging eliminates registration
errors due to mispositioning of the plates on the plate cylinders. It also
allows nonrandom or periodic color registration errors to be corrected
automatically by electronically controlling the relative phases of the
plate cylinders or the timing of the picture signals being applied to the
imaging apparatus at the various print stations so that the images applied
to the plates are shifted appropriately in phase. In the event that the
printing plates are imaged on press by imaging apparatus at each print
station, registration due to random gearing errors can be minimized
further by proper placement of the imaging apparatus. More particularly,
the imaging or writing head, e.g laser, spark discharge electrode, etc.
should be positioned opposite the plate cylinder so that an image dot
applied to that cylinder will offset to the impression cylinder or, more
particularly, to a paper sheet thereon, after the plate cylinder has
rotated exactly 360.degree.. With this constraint, if there are any random
gearing errors at any particular print station, these same errors will be
repeated in each identical sector of the impression cylinder gear that
defines a printing period or sector on that cylinder. Resultantly, the
same image dot will offset to the impression cylinder at exactly the same
location in each printing sector thereof. In effect then, the random
gearing errors are rendered cyclical or periodic so that they can be
compensated for electronically by appropriately controlling the timing of
the signal applied to the imaging head that produces that image dot.
Preferably, our press includes a computer terminal or workstation which
allows an operator to input data representing an original document or
picture to be printed, as well as a keyboard to permit the operator to key
in instructions regarding the particular press run, e.g. the number of
copies to be printed, the number of colors in the printed copies, etc. The
computer also allows complete control over the operating modes of the
press including printing plate imaging (if applicable), press startup
procedure, ink flow regulation, dampening, print, pause, as well as
shutdown and clean-up sequences. Desirably also, the workstation includes
a CRT display and the necessary internal memory to allow storage of the
impression or image data so that the impression to be printed can be
previewed before printing.
The press also includes provision for making ink adjustments automatically
depending upon the actual number of dots of each color in different bands
across the image, as opposed to the average number of color dots over the
entire picture area. This provides very accurate control over ink usage
and avoids the need of having a skilled technician present to effect the
ink regulation manually. This also minimizes the amount of paper waste
during set up.
A press made in accordance with this invention can print copies with as
many as 1016.times.1016 dots/inch (pixels/inch), with each dot being as
small as 1/2000 in..sup.2. The dots can be printed side by side or in an
overlapping relation to produce smooth, continuous color tones in the
printed copies. The press allows the printing of quick proofs as well as a
large quantity of proofs in the event that distribution of same is
required to a number of different people. If corrections are required, the
corrections can be entered at the prepress workstation and new plates
created reflecting the necessary changes. Then corrected copies can be
printed on a small volume basis or in quantity. If unusually long print
runs are required, e.g. in excess of 10,000 copies, new printing plates
identical to the previous ones can be made from the data already stored on
the press workstation. With all of these advantages, then, our press
should find wide application wherever there is a need to print high
quality color copies at reasonably low cost and with a great amount of
flexibility in the printing operation.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and objects of the invention,
reference should be had to the following detailed description, taken in
connection with the accompanying drawings, in which:
FIG. 1 is a side elevational view of an offset color press incorporating
our invention;
FIG. 2 is an end view of a portion of the FIG. 1 press;
FIG. 3 is an elevational view showing the opposite or gear side of a
portion of the FIG. 1 press;
FIG. 4 is an isometric view illustrating the manufacture of the impression
cylinder gear shown in FIG. 3;
FIG. 5 is a diagrammatic view of the FIG. 3 gear side of the press
illustrating the operation of the press.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 of the drawings, the illustrative embodiment of our
press, shown generally at 10, is a freestanding, sheet-fed four-color
offset press. The components of the press are mounted on an upstanding
machine frame 12 which normally rests on the floor and is only about seven
feet long. The press includes an internal controller 14 which receives
input data and control signals from a separate workstation 16 connected to
controller 14 by suitable cables. The press responds to digital signals
representing an original document or image and since the press is a four
color press, up to four separate strings of color signals are involved
representing the color separations for cyan, yellow, magenta and black.
These image signals may be stored on a disk and applied to the press by
way of a disc drive 16a at workstation 16. Alternatively, they may arrive
from a computer, telephone line or other source. Control signals for the
press are entered by an operator via a keyboard 16b at the workstation.
Using the keyboard, the operator may enter instructions for imaging the
printing plates on press, e.g. instructions relating to press control such
as ink flow adjustment, number of copies to be printed, etc.
Referring now to FIGS. 1 and 2, rotatively mounted on frame 12 is a large
diameter impression cylinder 22 having a central axle 24 journaled in
opposite sides of the machine frame 12. Typically, cylinder 22 is in the
order of 94 inches in diameter. | | |
