Method Of And Apparatus For Giving Information On The Ink Requirements Of A Printing Forme

Abstract

The present invention relates to a method which enables information to be given on the ink requirements of a printing forme, this method consisting of analyzing, in the flat state and at one pass, by light measurements, all the columns of the photo-engraving film of the printing forme, each in the aggregate, and then recording the information obtained. The invention also relates to a device for carrying this method into effect, which device comprises a single photoelectric cell of large size for each column to be analyzed, and a recording device for the information obtained.

Description

The present invention has for its object a method and a device which make it possible to give information on the ink requirements of a printing forme, which information will subsequently be utilized to regulate the feed of ink "per column" from the inking troughs of printing sets. (By the word "column" there will be understood the virtual division into columns which is generally considered as a printing forme). The "typograph" and "offset" methods of printing utilize, in order to regulate the quantity of ink in each column, a deformable metal blade which comes in proximity to an inking roller dipping in the ink, and thus limits at each point of a generator line of the roller, the thickness of the film of ink sent to the printing forme.

The deformable blade is generally applied against the roller by a large number of screws or other regulating means (one per column or even more) which define at this point the space between the inking roller and the blade. Sometimes also each column is supplied with ink by a piston pump having a variable travel.

The adjustment of the screws is generally carried out manually by operators who watch the printed paper in order to determine in which columns there is too much or not enough ink, and who vary the positions of the screws in consequence.

A preliminary adjustment may be made by observing on the printing forme vertically above each inking screw, the size of the surface to be printed in this column.

These adjustments have the disadvantage of being long and of necessitating a degree of interpretation.

In the pre-adjustment phase by examination of the plate, they necessitate an evaluation of the quantity of ink to be put into each column, this quantity being proportional to the surface printed.

The present invention relates to a method which enables information to be given on the ink requirements of a printing forme, this method consisting of analyzing, in the flat state and at one pass, all the columns of the photo-engraving film of the printing forme, each in the aggregate, and then recording the information obtained.

This invention also relates to a device for carrying this method into effect, which device comprises a single photo-electric cell of large size for each column to be analyzed, and a recording device for the information obtained.

Other characteristic features and advantages of the present invention will become apparent from the description which follows below, reference being made to the accompanying drawings, in which:

FIG. 1 is a diagrammatic exploded view in perspective of a device according to the invention;

FIG. 2 is a view in cross-section to a larger scale of the assembly permitting the analysis of the photo-engraving film;

FIG. 3 shows the block diagram of a possible example of the recording of the information on a perforated strip.

According to the invention, the method which enables information to be given on the requirements in ink of a printing forme consists of the analysis by densitometry in the flat position and at a single pass, of all the columns of a "typon" or photo-engraving film of the printing forme.

In this connection, it should be noted that, according to the type of the offset plates, the film is either a "positive" or a "negative" of the image to be obtained on paper. The surface to be printed is either directly proportional to the black of the film (the case of the positive film) or to the white (in the case of the negative film). The proportions supplied by the analysis must be corrected correspondingly.

However, the invention is applicable to both cases. It must also be noted that the term "black" employed here means "surface to be printed" without prejudice to the colour concerned. The method is suitable for the analysis of all colours.

The film is analyzed, preferably suspended in a vertical plane, without any part being in movement. It is converted to a suitable document in the photoengraving laboratory itself. By this means, any loss, damage or degradation is avoided which would be possible if the film had to be conveyed to the proximity of the printing press. Only the documents coming from the analysis will be conveyed to the printing press.

In the form of embodiment shown in FIGS. 1 and 2, the device according to the invention comprises a lightbox 1 designed so as to provide an illumination which is as uniform as possible on a ground-glass screen 2.

This light-box contains fluorescent tubes 3 or any other appropriate lighting device. The typon or film document to be analyzed 4 is placed like a sandwich between the light-box and a battery 5 of photo-electric cells.

On one face, the document is thus in direct contact with the photo-electric cells while its other face is in contact with the ground-glass screen.

The photo-electric cells 5 are equal in number to the number of columns of the printing forme.

Each cell 5, connected to a variable-load resistance 6, supplies a voltage which, amplified by direct-current amplifiers 7, is applied to one of the inputs of a scanning recorder (a cathode-ray tube 8 for example, on which the voltages coming from the cells 5 are switched cyclically during the horizontal scanning).

With a cell having a stop layer delivering into a resistance of a few ohms, there is obtained at the terminals of the resistance a voltage proportional to the illumination. A linear direct-current amplifier is therefore entirely suitable. If, on the other hand, the response of the cell employed is not linear, it is desirable to utilize an operational amplifier which restores the linearity.

There may be employed as cells "selenium photo-cells" or "selenium cells with a stop-layer." It is also possible to utilize any other type of photo-emitting or photo-resistant cell; the type of cell is of little importance provided that its dimensions may be that of a complete column.

It is also necessary that the type of cell utilized should have a response proportional to the illumination, or that the amplification circuit has a response curve adapted.

In FIG. 2, the film 4 is shown between the diffusing ground-glass screen 2 and a glass 9 for protecting the cells 5, the film being suspended from two marker pins 10 (see also FIG. 1). The panel of cells is fixed on an insulating support 11 and a plate of foam rubber 12 is placed between the insulating support 11 and a closure plate 13 of the light-box.

The device is used in the following manner:

A completely clear film being placed in the device between the light-box 1 and the cells 5, the operator adjusts the various resistances 6 so as to obtain a horizontal line on the cathode-ray tube 8. This line will be the zero line of the curve to be drawn by the apparatus.

The gain of the amplifiers is adjusted so as to be identically the same in all the amplifying systems.

The value 100 is defined as being the position of the spots on the cathode-ray tube when an entirely opaque film is placed in the device.

When a normal photo-engraving film is placed in the apparatus, each spot is deflected in proportion to the surface to be printed which is found in the column considered. It is then possible to take on the cathode-ray tube an extract by hand of the curve of the surfaces to be printed per column. The screen of the tube may also be photographed.

In order to regulate the feed of ink from the inking trough concerned, it is only necessary for the operator to refer to the extract of the curve of the surfaces to be printed and to adjust each feed correspondingly.

The invention provides other means of recording and transmission of information, by perforated tape, magnetic tape or any other appropriate information support.

In the form of embodiment shown in FIG. 3, the invention permits the recording of the information on a perforated strip or a magnetic tape. It comprises:

A change-over switching unit 14 making it possible to deliver successively and in sequence one of the voltages supplied by the cells 5;

An analogue digital interface 15 produces from the voltage supplied at each instant from a cell that is being considered, digital information suitable for actuating a strip perforating device or a magnetic tape;

A strip perforating device 16 or a magnetic recorder converting the voltages to coded signs;

A keyboard 17 permitting the operator to indicate on the perforated strip the reference of the inking trough for which the information is intended;

Finally a ring counter 18, the forward movement of which is determined by the signal 19 signifying the end of recording of each information, this signal being produced by the strip perforating device or by the tape recorder.

In order to record the information given by the analysis of the typon film, the method of utilization is as follows:

By means of the keyboard 17, the operator types the code number of the inking trough for which the information is intended. This code number is recorded on the perforated strip, and the ring counter 18 is set at the zero position (signal 20).

As soon as the code number is recorded, the ring counter passes into the position 1 and causes the opening of the channel 1 of the switching unit 14, thus permitting the passage of the voltage coming from the cell 1 towards the strip perforating device.

When the recording of the information coming from the cell 1 is completed, a signal 19 of the end of recording opens the passage to the channel 2 and effects the perforation of the signals coming from the cell 2 and so on until all the cells are exhausted. The device stops and signals to the operator that the cycle is completed. The operator may then cut the strip and send it to the press for use. He may also carry out the analysis of another film and the recording of the information given by this analysis.

It will of course be understood that the present invention has only been described and illustrated by way of a preferred example, and that equivalents may be introduced into its constituent elements without thereby departing from the scope of the said invention, as defined in the appended claims.

Claims

I claim:

1. Apparatus for determining a plurality of settings which control the amount of ink applied to respective circumferential columns of a printing forme used to effect the printing of an image comprising means for supporting an image member having an image thereon corresponding to the image to be printed from said forme, the image on said image member having column areas corresponding to said columns on the forme, a photosensitive area disposed to receive light from said image member with said photosensitive area being large enough to receive the light at one time from the entire area of a plurality of the column areas of the image on the image member, means for directing light onto the whole of a plurality of column areas on said image member, to transmit light to the photosensitive area and to establish over corresponding column areas of the photosensitive area a light intensity which indicates the image density in the corresponding column area of the image member and means for deriving from each of said photosensitive column areas a respective electrical signal depending on the amount of light on the column area.

2. Apparatus for predetermining settings of a plurality of ink control devices as defined in claim 1, and wherein said image member corresponds to the full image to be printed and wherein said photosensitive area receives light at one time from the full image, said image member being a light transmitting member and said means for directing light onto said image member being disposed on a side of said image member remote from said photosensitive area, said photosensitive area being disposed immediately adjacent said image member.

3. Apparatus as defined in claim 2 wherein said image member is flat and said means supporting said image member supports the latter in a flat position.

4. Apparatus as defined in claim 1 and wherein said photosensitive area comprises a plurality of photoelectric cells each of a size to receive light corresponding to a respective column area, and wherein said means for deriving a respective electrical signal from each of said photosensitive column areas comprises means for deriving a respective electrical signal from each corresponding respective one of said photoelectric cells.

5. Apparatus as defined in claim 4 and wherein said cells are arranged side by side as a panel corresponding to said image member.

6. Apparatus as defined in claim 4 and wherein each of said photoelectric cells comprises a selenium cell with a stop layer.

7. Apparatus as defined in claim 1 and further comprising means for recording said respective electrical signals derived from each of said photosensitive column areas.

8. Apparatus as defined in claim 7 and wherein said means for recording is a perforated strip recorder.

9. Apparatus as defined in claim 7 and wherein said means for recording is a magnetic tape recorder.

10. Apparatus as defined in claim 3 and wherein said means for directing light onto said image member comprises a source of light providing a substantially uniformly diffused illumination of said image member and wherein said image member comprises a film.

11. A method of providing information regarding requirements of ink for a printing forme comprising directing light onto an image member having the image to be printed thereon to illuminate the entire image area, transmitting light from the image member which varies spatially in intensity in accordance with the density of the image to be printed and illuminating therewith a photosensitive area with the photosensitive area receiving light from all portions of the image on the image member and deriving a plurality of signals from individual portions of the photosensitive area which correspond to columns of the printing forme used to print the image in which the ink flow to the respective column is controlled by a respective setting, the signal derived being a signal indicating the amount of light falling on the corresponding column area of the photosensitive area, and utilizing the electrical signals to indicate the ink settings for the columns of the printing forme.