U.S. patent number 3,760,098 [Application Number 05/201,025] was granted by the patent office on 1973-09-18 for method and apparatus for the seamless engraving of half-tone printing plates.
This patent grant is currently assigned to N.V. Werkspoon-Amsterdam. Invention is credited to Ferdinand Allard DE Vos, Jan Hendrik Terter Steege.
United States Patent |
3,760,098 |
DE Vos , et al. |
September 18, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
METHOD AND APPARATUS FOR THE SEAMLESS ENGRAVING OF HALF-TONE
PRINTING PLATES
Abstract
Method and apparatus is provided for point by point and line by
line production of half-tone printing cylinders which are seamless
in a direction perpendicular to the direction of the lines from a
cylindrical master having a seam in that direction. The surfae of
the master, including the seam, is scanned to produce a selected
number of engraving signals per revolution of the master and
printing cylinders. Of these, a certain small number will
correspond to the seam on the master and these are eliminated on
the printing cylinder and the engraved image on the printing
cylinder is "stretched" a corresponding number of engraving points
by repeating the engraving of a number of scanning points on the
master image.
Inventors: |
DE Vos; Ferdinand Allard
(Castricum, NL), Steege; Jan Hendrik Terter (Abcoude,
NL) |
Assignee: |
N.V. Werkspoon-Amsterdam
(Amsterdam, NL)
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Family
ID: |
19806720 |
Appl.
No.: |
05/201,025 |
Filed: |
November 22, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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25978 |
Apr 4, 1970 |
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Foreign Application Priority Data
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Apr 17, 1969 [NL] |
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6905923 |
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Current U.S.
Class: |
358/3.3; 358/409;
358/474 |
Current CPC
Class: |
H04N
1/38 (20130101) |
Current International
Class: |
H04N
1/38 (20060101); H04n 005/78 (); H04n 001/38 () |
Field of
Search: |
;178/6.6R,6.6B,6.7R,13,6.6DO,6.6DD |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Konick; Bernard
Assistant Examiner: Lucas; Jay P.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a Continuation-In-Part of parent application Ser. No.
25,978 filed Apr. 4, 1970 and now abandoned.
Claims
What Is claimed Is;
1. In a system for producing half-tone screen printing
cylinders:
a master cylinder having an image portion interrupted
circumferentially by a seam of known circumferential width;
a printing cylinder upon which the image on said master cylinder,
at least substantially exclusive of said seam, is to be
engraved;
means for circumferentially scanning said master cylinder to
produce a selected number of engraving signals per complete
circumferential scan cycle and including a number of certain
engraving signals corresponding to the circumferential width of
said seam;
means for circumferentially engraving said printing cylinder in
accord with said engraving signals during each engrave cycle,
and
means for causing a selected number of said engraving signals
corresponding to different parts of said image portion from
throughout said image to be engraved twice and a corresponding
selected number of said certain engraving signals corresponding to
said seam to be skipped during each circumferential engrave
cycle.
2. In a system for producing half-tone screen printing cylinders as
defined in claim 1 wherein said selected number of engraving
signals is substantially equal to said certain number of engraving
signals corresponding to said width of the seam.
3. In a system for producing half-tone screen printing cylinders as
defined in claim 1 wherein the last mentioned means comprises a
plurality of storage members connected as a serial shift register
and gate means for passing signals from one storage member at a
time to said means for engraving, said gate means including a
plurality of gates associated with said storage members and control
means for periodically stepping from one storage member to the next
as the output to said means for engraving.
4. In a system for producing half-tone screen printing cylinders as
defined in claim 3 wherein said plurality of gates is equal to one
more than said selected number of engraving signals to be
skipped.
5. In a system for producing half-tone screen printing cylinders as
defined in claim 4 wherein said engraving signals are connected to
the first of said series of storage members and the serial shift
register comprised of said storage members is shifted at the same
rate as the engraving signals are generated.
6. Apparatus for producing a half-tone image on a cylindrical
printing cylinder which occupies the entire circumference of the
printing cylinder along a certain length thereof and which is
derived from an image on a master cylinder which occupies slightly
less than the full circumference thereof due to the presence of a
longitudinal seam, said apparatus comprising:
means for rotating said master cylinder and said printing cylinder
in unison;
means for scanning said master cylinder point-by-point and
line-by-line over the longitudinal length of the image thereon, and
for producing a selected number of point-by-point engraving signals
per complete revolution of said master cylinder and said printing
cylinder whereby certain of said engraving signals per revolution
correspond to the presence of said seam;
means for engraving said printing cylinder point-by-point and
line-by-line in accord with said engraving signals and to produce,
per complete revolution of said printing cylinder, a number of
engraving points equal to said selected number of engraving
signals; and
means for eliminating at least substantially all of said certain
engraving signals per revolution which correspond to said seam and
replacing them by repeated engraving signals generated from
different portions of said image from throughout said image on the
master cylinder.
7. Apparatus according to claim 6 wherein the last means comprises
serial shift register means receiving said engraving signals,
control means for shifting out said shift register means in
parallel, and gate means for selecting one of the parallel outputs
at a time to control said means for engraving.
8. Apparatus according to claim 7 wherein said gate means includes
a number of serially selected gates equal in number to one more
than the number of engraving signals which are eliminated per
revolution.
9. The method of producing a half-tone image on a cylinder printing
cylinder which occupies the entire circumference of the printing
cylinder along a certain length thereof and which is derived from
an image on a master cylinder which occupies slightly less than the
full circumference thereof due to the presence of a longitudinal
seam, which comprises the steps of:
a. rotating the master and printing cylinders in unison while
scanning the surface of the master cylinder point-by-point and
line-by-line at a selected scanning point rate per revolution;
b. engraving the printing cylinder point-by-point and line-by-line
at the same rate per revolution as the scanning of step (a);
and
c. during each revolution in step (b), skipping those scanning
points corresponding to at least a major portion of the seam and
substituting therefor repetitively engraved scanning points derived
from different portions of the image from throughout said image on
the master cylinder.
10. The method of producing a half-tone image as defined in claim 9
wherein the repetitively engraved scanning points of step (c) are
distributed throughout the image on the printing cylinder.
11. The method of producing a half-tone image as defined in claim
10 wherein each repetitively engraved scanning point is engraved
twice in succession.
12. Apparatus for producing a half-tone image on a cylindrical
printing cylinder which occupies the entire circumference of the
printing cylinder along a certain length thereof and which is
derived from an image on a master cylinder which occupies slightly
less than the full circumference thereof due to the presence of a
longitudinal seam, said apparatus comprising:
means for rotating said master cylinder and said printing cylinder
in unison;
means for scanning said master cylinder point-by-point and
line-by-line over the longitudinal length of the image thereon, and
for producing a selected number of point-by-point engraving signals
per complete revolution of said master cylinder and said printing
cylinder whereby certain of said engraving signals per revolution
correspond to the presence of said seam;
means for engraving said printing cylinder point-by-point and
line-by-line in accord with said engraving signals and to produce,
per complete revolution of said printing cylinder, a number of
engraving points equal to said selected number of engraving
signals;
means for eliminating substantially all of said certain engraving
signals per revolution which correspond to said seam; and
means for repeating a sufficient number of engraving signals
generated from different portions of said image, from throughout
said image on the master cylinder remote from said seam as to
replace the eliminated engraving signals.
Description
BACKGROUND OF THE INVENTION
In the production of cylindrical half-tone printing plates there is
the difficulty that the master disposed on a cylinder has a seam
extending transversely to the line direction and situated where the
edges of the fitted master abut each other, thus forming a joint.
The master is therefore interrupted over some distance, so that a
printing plate engraved from this master would also have a seam.
This is undesirable, however, because with continuous printing from
such a half-tone printing plate the product would repeatedly be
interrupted by seams. Various attempts have already been made to
reduce the seam in the master to a very small size, but these
attempts have not yielded the desired result.
BRIEF SUMMARY OF THE INVENTION
The invention provides apparatus and method for the production of a
seamless half-tone printing plate wherein a number of points are
repeatedly engraved in the line direction. The number of points
thus engraved is so chosen that the seam is entirely bridged.
Preferably, the points repeatedly engraved on a line are
staggered--in the line direction in relation to the points
repeatedly engraved on the adjacent lines, as disclosed in
copending application Ser. No. 185,946 filed Oct. 4, 1971. This
prevents the repeatedly engraved points from being disposed on a
straight line, which could cause a blemish in a print made with
this half-tone printing plate.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a combined view showing principal portions of the
apparatus and including circuit components for carrying out the
invention; and
FIGS. 2 and 3 are diagrammatic time diagrams illustrating certain
aspects of the invention.
The master 2 disposed on the rotatable cylinder 1 has a seam 3
which extends approximately at right angles to the line direction
in which the master 2 is scanned and which seam occupies a small
but finite number of total scan points per revolution of the
cylinder. The scanning of the master rotating with the cylinder 1
is performed pointwise by means of the scanning element 4, which
measures the intensity of the light which is emitted by the lamp 5
and reflected by the master. The number of scan points per
revolution of the cylinder is controlled by a screen generator 24
deriving its signals from the shaft which drives the cylinder and
providing a fixed number of control signals per revolution. The
screen generator 24 provides these output signals at the conductor
45 which are applied to shift the registers 18-23 and these signals
are also used to control the output of the converter 17, as
indicated by the conductor 46, and the engraving control converter
32, as well, is controlled in accord with the screen generator
frequency as symbolically indicated by the conductor 47. Details of
the screen generator and the converters are disclosed in copending
applications Ser. Nos. 185,946 and 185,947, filed Oct. 4, 1971 and
incorporated herein by reference.
The engraving element 6 engraves the plate 8 disposed on the
cylinder 7 and thereby produces a half-tone printing plate. The
cylinders 1 and 7 are disposed on the same shaft and rotate
synchronously. Two signal transmitters 9 and 10 are disposed on the
same shaft as the cylinders 1 and 7. The signal transmitters 9 and
10 each comprise a cylindrical part 11 and 12 formed with a number
of apertures, a lamp 13 and 14 respectively on the inside of the
cylindrical part 11 and 12 respectively, and a photo-electric cell
15 and 16 respectively on the outside of the cylindrical part. At
the instant when, during the rotation of the cylindrical part, an
aperture in the cylindrical wall is situated between the lamp and
the photo-electric cell, a signal is generated. The cylindrical
parts 11 and 12 rotate synchronously with the cylinders 1 and 7.
The analogue information scanned by the scanning element 4 is
converted into digital information in the circuit 17. From the
circuit 17 the digital information can be fed to the first (18) of
a number of memory cells 18-23. These memory cells 18-23 are
connected as a serial shift register. The control pulses for
shifting the information through the shift register are derived
with the aid of the circuit 24 from the screen frequency.
Associated with the respective memory cells 18-23 are the AND-gates
25-30. The output of each AND-gate is connected to the input of an
OR-gate 31. The output of the OR-gate 31 is connected to the
circuit 32 which converts the information obtained from the OR-gate
31 into control signals for the engraving element 6. At any
particular time one and only one of the AND-gates 25-30 is open for
passing on the contents of the associated memory cell to the
OR-gate 31. The AND-gate which is open is determined by the
contents of the 3-bits register comprising the bistables 33, 34 and
35, the output of each of which is connected to the decoding
circuit 36. The decoding circuit 36 has six outputs 37-42. Output
37 is connected to an input of the gate 25, output 38 is connected
to an input of gate 26, etc. Of the six outputs 37-42, one and only
one is energized at any particular time to enable a respective AND
gate. Each time a pulse is emitted by the photo-electric cell
through the agency of the circuit 43, the contents of the 3-bits
register 33, 34 and 35 are increased by "1". During each revolution
of the cylinders 1 and 7 the bistables 33, 34 and 35 and the memory
cells 18-23 are reset by a pulse from the photoelectric cell 15
through the agency of the circuit 44.
The apparatus functions as follows. When the aperture in the
cylindrical part 11 passes the photo-electric cell 15, the circuit
44 emits a pulse which resets the two registers 33, 34, 35 and
18-23. During the continuing rotation of the cylinders 1 and 7 the
information relating to the scanned point of the master 2 from the
analogue-digital converter 17 is fed, at the screen frequency, into
the memory cell 18. When the next point in the line direction is
scanned, the information relating to the previously scanned point
is transferred to the memory cell 19, while the information
relating to the present point is again fed into the memory cell 18.
When six points on a line have consecutively been scanned, the
entire register 18-23 is filled with information relating to the
six points which have been scanned. When the seventh point is
scanned, the information relating to the first point, which
information was in the memory cell 23, is lost. During this time,
the contents of the register 33, 34, 35 is such that the output 36
is energized, so that the gate 25 is open and the information is
fed from the memory cell 18 through the gate 25 and the gate 31 to
the circuit 32 which emits the control signals for the engraving
element 6. Therefore up to the instant when the contents of the
register 33, 34, 35 change, the point last scanned is always
engraved. When an aperture in the cylindrical part 10 passes the
photo-electric cell 16, a pulse is generated which is fed through
the circuit 43 to the register 33, 34, 35 whose contents are
consequently increased by "1". Since the register 33, 34, 35 now
contains the value "1", the output 38 is energized and the gate 26
is opened, while the gate 25 closes. Now therefore the information
relating to the point which is in the memory cell 19 is engraved.
The first point which is now engraved is the same point as the one
last engraved from the memory cell 18, since the information in the
memory cell 18 has been shifted to memory cell 19. The point
concerned is therefore engraved twice in succession. Thereafter the
point penultimately scanned is engraved each time. This continues
in this way until the next pulse from the photo-electric cell 16
causes the contents of the register 33, 34, 35 to be increased by
"1". Then the memory cell 20 is selected and a corresponding point
is engraved twice.
To illustrate the principles according to the present invention,
let it be assumed that the screen generator 24 generates three
hundred control signals per revolution of the cylinder 1 and that
the disc 9 has its opening so set as to create a reset signal for
the registers 18-23 and for the registers 33, 34 and 35 just after
the scanning head 4 has passed the seam 3 but before the first
scanning point on the cylinder 1 beyond the seam is reached. Let it
also be assumed that the seam 3 occupies a width on the cylinder 1
corresponding to 5 scanning points. Let it further be assumed that
the disc 10 contains five openings so that there are five signals
to step from the gate 25 to the gate 26; from the gate 26 to the
gate 27 and so on until the last step from the gate 29 to the gate
30, and that these stepping pulses occur just after the 30th, 90th,
150th, 210th and 270th scanning points, the first scanning point
being the first point just after the seam 3. Under these
conditions, the 30th, 89th, 148th, 207th, and 266th scanning points
will be engraved twice and, moreover, all five scanning points
corresponding to the seal 3 will be skipped.
To illustrate how this occurs, reference is now had to FIG. 2
wherein the registers 18-23 contain, at the 300th scanning point
which corresponds to the last point on the seam 3 just before the
image on the cylinder 1 again begins, all five of the scanning
points corresponding to the seam 3, that is the 296th-300th
scanning points will be contained in the registers 15-22 whereas
the last scanning point on the image prior to the seam 3, the 295th
scanning point, will be in the register 23 and will be read out, as
indicated, because the gate 30 is enabled.
If there were no resetting of the registers, the next scanning
point after the situation of FIG. 2 would be as depicted in FIG. 3,
wherein the various registers 18-23 contain the scanning points as
noted in FIG. 3. Of course, the registers have been reset just
prior to the first scanning point so that, in actuality, the
situation of FIG. 3 is accurate only as to the first register 18,
the remaining registers 19-23 being empty.
Thus, by cycling back from the last register 23 as indicated in
FIG. 2 back to the register 18 as indicated in FIG. 3, all five
scanning points containing the seam scans will be skipped. Thus, it
will be seen that the number of scanning points which may be
skipped is one less than the number of gates 25-30 and that the
number of openings in the disc 10 is not more than this number
although, as is evident it could be less. That is to say, the
number of scanning points on the entire circumference of the
cylinder 1 which will be skipped and which are chosen to correspond
to the seam area 3 is equal to the number of openings in the disc
10 since, for each opening in the disc 10, one of the scanning
points on the image portion of the cylinder, exclusive of the seam
3 will be engraved twice and, to accommodate for this, there must
be a number of gates 25-30 which is one greater than the number of
scanning points which are engraved twice.
It is further to be understood that the analog-to-digital converter
17, although shown with only one output conductor 48 issuing
therefrom, in reality will contain a number of output conductors
each having the bit of a binary word thereon. Preferably, the
binary words from the converter 17 are five-bit binary words so as
to allow a maximum of 32 scanning levels to be accommodated for
and, correspondingly, there will be five sets of registers 18-23
and five corresponding sets of AND gates 25-30 and five OR gates
31, all feeding into the digital-to-analog converter 32 to provide
in each instance a single analog output signal for actuating the
engraving head 6.
Ordinarily, the width of the seam on the master will be in the
order of five or six scanning points so that the capability of
eliminating five scanning points on the seam as specifically
disclosed will be entirely adequate. That is to say, it is not
essential that every scanning point of the seam be eliminated,
material reduction in its width as engraved may be sufficient under
some circumstances. If a seam, on the other hand, were to be of
substantially less width-say only two scanning points wide-the use
of a disc 10 having only two openings is sufficient completely to
eliminate it, in which case only three of the gates 25-30 would be
functioning for this purpose.
* * * * *