GB2132754A

GB2132754A - Determination of print area of a printing master

Info

Publication number: GB2132754A
Application number: GB08332168A
Authority: GB
Inventors: Bernd Morgenstern; Helmut Weigend; Wolfgang Beyer
Original assignee: Kombinat Polygraph Werner Lamberz VEB; Polygraph Leipzig Kombinat Veb
Current assignee: Kombinat Polygraph Werner Lamberz VEB; Polygraph Leipzig Kombinat Veb
Priority date: 1982-12-29
Filing date: 1983-12-01
Publication date: 1984-07-11
Also published as: GB8332168D0; DE3338883A1; DD226150A3; FR2538761B1; FR2538761A1; JPS59123669A; GB2132754B

Abstract

A method of determining the print area portion of a printing original, outside or inside a printing machine, with the use of incident or transmitted light comprises the step of initially tightening the original on a curved or planar support by means of a mechanical tension force. A row of photoelectric diodes (2.1 to 2.5) on a rail (8) are calibrated simultaneously by calibration standards (3, 4) extending transversely of the diode conveying direction before movement of the row into the printing image region of the original. The original, divided into columns (1.1 to 1.5) is then scanned in small areas starting in all columns at the same time, and the resulting measurement values are stored in a computer and integrated for the purpose of formation of the desired indication of the print area. <IMAGE>

Description

SPECIFICATION Determination of the print area of a printing master The present invention relates to a method of determining the print area of a printing master, either outside or inside a printing machine and particularly with use of incident or transmitted light, and to apparatus for use in carrying out such a method.

In DE-OS 30 29 273 there is disclosed apparatus for measurement of the printing image region of an offset printing plate, in which apparatus a rectilinear photoelectric detector is used for optical scanning and determining of the print and print-free areas of the plate with calibration mark. A conveying device transports the printing plate or the detector so that the latter scans the plate. Evaluation and determination of the print image area is undertaken by a processor unit, for which a calibration is performed and the image region is ascertained according to the kind of plate.

It is in that case disadvantageous that an expensive photoelectric detector is necessary for the measurement of the print image region and that although the measurement error caused by thermal deformations is reduced by the use of two linear light sources parallel to each other, it is not eliminated.

It would thus be desirable to provide a method and apparatus for the determination of the print area portion of a master with use of a less expensive photoelectric detector which provides higher measurement accuracy.

According to a first aspect of the present invention there is provided a method of determining the printing area portion of an original by optical scanning and determining the print area and the print-free area in that the original or the photoelectric detector equipment is positioned by means of a conveying device and the basic photoelectric elements are calibrated by means of calibration standards, wherein the original is tightened on a curved or planar base support by means of a mechanical tension force, all sensor fields arranged on a fastening rail are calibrated simultaneously by calibration standards disposed transversely of the conveying direction before the transport to the printing image region of the original, the original, divided into columns, is scanned in small areas starting in all columns at the same time, and the measurement values are stored in a calculator and integrated for the purpose of formation of the amount.

Advantageously, the scanning of the original is carried out in such a manner that the scanning in small areas starting in all columns at the same time takes place in meander shape within the columns.

For a scanning in particularly small areas, it is favourable to undertake the scanning within partial columns along the columns, each having the width of an ink zone, of the original.

Preferably, the original, through clamping onto an impression cylinder, receives the original position.

According to a second aspect of the present invention there is provided apparatus for use in carrying out the method of the first aspect of the invention, the apparatus comprising equally spaced sensor elements arranged at a fastening device in detector equipment, the fastening device being connected with a conveying device for the generation of a transverse and longitudinal movement.

An example of the method and an embodiment of the apparatus of the present invention will now be more particularly described with reference to the accompanying drawing, the single figure of which is a schematic plan view of apparatus embodying the invention.

Referring now to the drawing, there is shown scanning apparatus comprising a row of equidistantly spaced apart photoelectric area diodes 2.1 to 2.5 arranged on a rail 8, the rail being displaceable by a transport device 5 to move the diodes in directions 7 parallel to, and a direction 6 transverse to, the row so that each diode is movable on a meandering path along a respective one of columns 1.1 to 1.5 of the original. Each of the columns 1.1 to 1.5 has the width of an ink zone of the original.

Before the actual measuring operation starts, the diodes 2.1 to 2.5 are calibrated during transport over calibration standards 3 and 4.

To effect scanning, the transport device 5 displaces the rail 8, after a first measuring operation of the diodes by reflected or transmitted light, in the direction 7 so as to position each diode in a second area, of the size of the diode itself, of the respective column. This movement is performed at a high speed by, for example, a pulse-controlled solenoid, a stepping motor or similar. The width of each diode thus corresponds to half the width of the respective column. When measurement in the second area has been completed, the rail 8 is displaced in the main scanning direction 6 to align the row of diodes with the next line of the original. The movement of each diode in that case is equal to its dimension transversely of the row.

When the measurement values provided by the diodes have been stored, the movement of each diode to a second area, of the size of the diode, of the respective column again takes place and this pattern of movement is repeated. As a result, a meander-shaped scanning path 9 is obtained.

In this method, fewer scanning elements are needed for the scanning of the original and costs are thereby reduced compared with the use of a completed diode line.

Thermal deformations brought about during heating of the original, for example a printing plate, and the resulting unevenness can falsify the values of the intensity changes of the transmitted or reflected light, The consequence is a deviation of the determined print image region from the actual and exact determination of the quantity of the required ink is not possible. In order to make these deformations ineffective during the measuring operation, the original is tightened at its edges by means of a mechanical tension force which can, for example, be provided by a fastening rail and a spring system.By contrast to the known apparatus with two light sources which are parallel to the printing plate and which must be arranged at a certain spacing therefrom, the method exemplifying the present invention does not set out to optimise measurement values but instead eliminates the source of measurement value errors.

The diodes 2.1 to 2.5 are each connected to the input of a respective amplifier which is connected at its output to a multiplex unit.

The analog values at the output of the multiplex unit are converted by an analog-to-digital converter into digital signals. These digital signals are fed to a microcomputer which stores and integrates the values. After each change-over of the transport device 5, interrogation of the measurement values is effected again by the multiplex unit.

In the case of a method exemplifying and apparatus embodying the present invention, fewer photoelectric base elements are necessary for the detector and the thermal deformations of the original to be measured are eliminated during the measurement operation.

Claims

1. A method of determining the print area of a printing master by means of a row of optical scanning elements, the method comprising the steps of mounting the master under tension on a support, calibrating the scanning elements simultaneously, before disposition thereof in the image region of the mounted master, by means of a calibration strip extending along the row, relatively displacing the row and the master to cause the calibrated elements to simultaneously scan respective column-shaped portions of the master area-by-area and thereby provide measurements of the print and print4ree portions of the master and processing the measurements to determine said print area.

2. A method as claimed in claim 1, wherein the step of processing comprises storing and integrating the measurements in calculating means.

3. A method as claimed in either claim 1 or claim 2, wherein the step of relatively displacing is carried out in such a manner as to cause each scanning element to scan alternately across and along the respective column-shaped portion.

4. A method as claimed in any one of the preceding claims, wherein the step of relatively displacing is carried out in such a manner as to cause each scanning element to scan the respective column-shaped portion in length sections thereof.

5. A method as claimed in any one of the preceding claims, wherein the step of mounting comprises exerting a mechanical tension force on the master to tighten the master around a flat or curved surface portion of the support.

6. A method as claimed in claim 4, wherein the step of mounting comprises tightening the master around the circumference of an impression cylinder.

7. A method substantially as hereinbefore described with reference to the accompanying drawing.

8. Apparatus for use in carrying out the method claimed in claim 1, comprising a row of equidistantly-spaced optical scanning elements calibratable before operation by means of a calibration strip extending along the row, and displacing means for displacing the row in longitudinal and transverse directions thereof to effect simultaneous scanning by the elements of respective column-shaped portions of a tension-mounted printing master area-by-area so as to provide scanning measurements processable to determine the print area of the master.

9. Apparatus substantially as hereinbefore described with reference to the accompanying drawing.