US3664843A - Screen combination - Google Patents

Abstract

THE HEAD LINES OF THE SCREENS ARE USED IN PRINTING A PICTURE ARE PREFERABLY SLANT AND AT DIFFERENT ANGLES IN RELATION TO THE HEAD LINES OF THAT PICTURE. EVERY SCREEN DOT OF SUCH A SCREEN IS OBTAINED AT THE DEVICE DESCRIBED BY EXPOSURE OF A PHOTO-SENSITIVE LAYER, WHICH IS PROVIDED ON TO AN ETCHABLE SUBSTRATE, WITH THE AID OF AN ELECTRON BEAM. IN THE PROCESS A HEAD LINE OF THE PICTURE MOVES ACCORDING TO ITS OWN LENGTHWISE DIRECTION IN A PLANE PERPENDICULAR TO THE OPTICAL AXIS OF THE ELECTRON GUN. BY RENDERING THE ELECTRON BEAM FOR MANUFACTURING SPECIFIC DOTS OF THE SCREEN A DEVLINATION PERPENDICULAR TO THE SAID HEAD LINE AND/OR IN THE DIRECTION OF THE SAID HEAT LINE OF THE PICTURE A SCREEN IS CREATED WITH ITS TWO HEAD LINES SLANT IN RELATION O THE HEAD LINES OF THE PICTURE.

Description

May 23, 1972 FQNTIJN 3,664,843

SCREEN COMBINATION Filed June 9, 1970 FIG.1

INVENTOR.

MWJMI ZV;

United States Patent US. Cl. 96-116 7 Claims ABSTRACT OF THE DISCLOSURE The head lines of the screens used in printing a picture are preferably slant and at different angles in relation to the head lines of that picture.

Every screen dot of such a screen is obtained at the device described by exposure of a photo-sensitive layer, which is provided on to an etchable substrate, with the aid of an electron beam.

In the process a head line of the picture moves according to its own lengthwise direction in a plane perpendicular to the optical axis of the electron gun.

By rendering the electron beam for manufacturing specific dots of the screen a declination perpendicular to the said head line and/or in the direction of the said head line of the picture a screen is created with its two head lines slant in relation to the head lines of the picture.

The invention relates to a screen combination comprising a basic screen whose screen dots are placed on the angular points of squares and at least one screen rotated in relation to the basic screen, whose screen dots are also placed on angular points of squares.

Such a screen combination is known in the art.

This known combination comprises a screen that is rotated 15 in relation to the basic screen, a screen that is rotated 45 in relation to the basic screen and a screen that is rotated 75 in relation to the basic screen.

In order to obtain a rotated screen, the original of which a colour reproduction has to be made, is scanned, with regard to the intensity of a colour, at an angle that is as great as the angle the rotated screen must have in relation to the basic screen.

With the intensity-modulated signal a machine for engraving the rotated screen is fed. So in order to attain a screen combination the original must be scanned as many times and the engraving machine must be fed as many times as there are screens applied in the combination.

So manufacturing a combination of such screens requires much time and therefore is expensive.

The object of the invention is such a screen combination and with screen rotations chosenin such a way that the basic screen and the rotated screens can be engraved on a machine simultaneously with modulated signals originating from an original not rotated in relation to the basic screen and attached to the same machine.

The invention is therefore characterized in that the screens show a change in lineature in relation to the unit of length=l according to formula W I-p in which parameter x is a scale factor, parameters n and p are whole numbers and parameter n at the same time depends on the angle the head lines of the screens make with the edges of the pictures.

In order to attain simple electronics for and a simple qonstruction of the engraving machine for parameter ice n=1 the angular rotation is preferably chosen equal to 45 degrees, for n=2 equal to 26 degrees and 34 minutes, for n=3 equal to 18 degrees and 26 minutes and for n=4 equal to 14 degrees and 2 minutes.

The invention is preferably applied to a machine with rotating cylinders.

Then on the jacket of one of the cylinders the original that has to be scanned is mounted. The other cylinders are provided on their jackets with a layer to be exposed, which is exposed with a pulsating electron beam.

Scanning the picture is ettected according to a helix with a pitch that has been chosen identically to scale factor x multiplied with unit 1.

The screen dots to be engraved of rotated screens are not all of them lying on helices; by having small deviations of the electron beam make small deviations, all screen dots can be engraved after all.

So the rotated screens are engraved according to diagonal directions and angular dots that do not line on the diagonals are filled up by lateral displacements of the electron beam between the helices.

The invention will now further be elucidated with reference to a drawing with 5 figures.

In the drawing:

FIG. 1 represents the screen known in the art mostly suitable for use as basic screen.

FIG. 2 a screen according to a diagonal 1 over 1, also suitable as basic screen.

FIG. 2a a screen as shown in FIG. 2, however, with x= /2.

FIG. 3 a screen according to a diagonal 1 over 2 to the left or to the right.

FIG. 4 a screen according to a diagonal 1 over 3 to the left or to the right.

FIG. '5 a screen according to a diagonal 1 over 4 to the left or to the right.

In FIG. 1 a so-called straight screen is drawn with the head lines parallel to the edges of the picture.

The screen dots are placed on the angular points of squares, with a side length equal to the unit=1.

Such a screen can easily be made on an engraving machine, the original being mounted on a cylinder jacket and being scanned according to a helix with a pitch equal to the unit=1 multiplied with a factor x, if necessary, and the screen being obtained by point-by-point exposure of a layer on a second synchronously running cylinder.

Starting from the original on the machine now according to the invention it has become possible to manufacture simultaneously other screens whose head lines make ditferent angles with the head lines of the basic screen as shown in FIG. 1.

For this purpose it will be necessary that the exposure apparatuses are controllable, so that screen dots do not lie on'the helices according to the basic screen but somewhat outside of it and that moreover are somewhat shifted in relation to this screen can be engraved.

A device as described in U.S.A. patent application No. 827,510, for instance, is designable for the above purpose, by mounting to the electron beam exposing apparatus as described in this application a control by means of which the electron beam can be moved in the plane of engraving.

As will appear further the displacements must be effected in code, for they are connected with the angle the screen must obtain with the edges of the picture. The code can originate from a code disc that rotates along with the cylinder on which the original that is to be scanned is mounted.

For each part-colour in a colourprint the screen must make a specific angle with the edges of the picture.

If the original is composed of five colours then also five screens must be manufactured at five different angles.

For that purpose also five exposure apparatuses with five individual codings for localization of the dots are required.

Further moreover each exposure apparatus still is simultaneously and individually controlled in intensity by means of intensity-modulated colour signals obtained by scanning the original.

Q1 order to obtain a simple engraving apparatus the cy nders for engraving and the cylinder with the original a preferably mounted on to one shaft so that the drive and the pitch for engraving and scanning are identical. This is shown in FIGS. 1 to 5.

In the figures the pitches of the helical scanning and engraving are indicated by the letter S.

The screen dots are placed on the angular points of squares: for that purpose pitch S has been taken equal to the unit of length==l. Then for a straight" screen as has been shown in FIG. 1 it holds that the distance between the screen dots the so-called lineature is also equal to =1.

For a screen such as has been shown in FIG. 2, with the head lines running at 45 with the edges of the picture, the lineature becomes /2. Such a 1 over 1 screen (see the dotted lines in this figure) has only a few screen dots.

Coding is simple, again and again only one screen dot needs to be left out when engraving dots P P P which all of them are lying on one helix.

In the screen with head lines at 45 according to FIG.

2a the lineature becomes x/T.

The number of screen dots has considerably been increased. Dots P and P are again lying on one helix. For engraving the intermediate dot P the electron beam must be moved by /z to the left.

The code for this is simple to realize.

The lineature of the so-called I over 2 screen shown in FIG. 3 becomes Here dot P is also obtained by control by means of coding the electron beam of the engraving machine.

The lineature of the so-called 1 over 3 screen shown in FIG. 4 becomes ma t-1m Dots P and P are obtained by movement of the electron beam to the left while dots P and P are lying on a helix as a result of pitch S.

The lineature of the 1 over 4 screen shown in FIG. 5 is vm m m 4 T T a first plate having picture points located at the corners of said squares,

a second plate having picture points located at the corners of said squares and the pattern of dots is rotated relative to the pattern of dots of said first plate,

the lineation of said pattern of squares on each of said plates is formed according to the formula wherein x represents a scale factor, n and p are whole numbers in which n is a function of the lineation of said squares with respect to the edges of the picture.

2. The combination of printing plates as in claim 1 wherein for an angle of '45 degrees 11:1 and n=1.

3. The combination of printing plates as in claim 1 wherein for an angle of 20 degrees 34 minutes 11:1 and 12:2.

4. The combination of printing plates according to claim 1 wherein for an angle of 18 degrees 26 minutes 12:1 and n=3.

5. The combination of printing plates as in claim 1 wherein the angle is equal to 14 degrees 2 minutes for p='1 and "=4.

6. The combination of printing plates as in claim 1 wherein said first plate has headlines running parallel to the edges of said picture in magenta, said other plate represents cyanic, a third plate representing a screen wherein x=1 and n=2, and a fourth screen in yellow having parameters 20:1 and n=3, and said second screen is rotated in one direction with respect to said 'first screen, said third screen is rotated in the opposite direction with respect to said first screen, and said fourth screen is r0 tated in the same direction as said third screen.

7. The combination of printing plates as in claim 1 wherein said first screen has headlines running parallel to the edges of said picture in magenta, a second plate forming a screen in yellow with parameters x=1 and n=2, a third plate forming a screen in black, and a fourth plate forming a screen in cyanic, said third and fourth screens having parameters of x=1 and n= 3, said second screen is rotated in one direction with respect to said first screen, said third screen is rotated in the same direction as said second screen and said fourth screen is rotated in an opposite direction than said second screen with respect to said first screen.

References Cited UNITED STATES PATENTS 2,757,087 7/ 1956 Wicklund 96-116 3,085,878 4/1963 Archer 96--45 3,300,308 1/1967 Jemseby 96-45 2,864,700 4/ 1958 Chevalier 9645 3,040,644 6/1962 Hearther 9645 3,210,186 10/ 1965 Gorig 961l6 NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner US. Cl. X.R. 96-4l, 44, 45

NITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION A Patent No. 326641843 D t d May 3, 1972 I Inventor(s) Leendert FOntijn It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1: Line 13, should read: x n

Claim 3: Line 2, cancel 20" and insert --26-.

Claim 6: Line 2', after "wherein" insert -p l and--. Line 4, before wherein insert --'in blaok--.

Claim 7: Line 2-, after "wherein" insert --p l" and--.

Signed and sealed this 9th day of July 1971.

(SEAL) Attest: v

McCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents PC4050 uscoMM-oc 60376-P69 ".5. GOVERNMENT PRINTING OFF'CE 2 9.9 0-366-334,

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