GB2288669A

GB2288669A - Method of controlling the imaging of a printing forme

Info

Publication number: GB2288669A
Application number: GB9507549A
Authority: GB
Inventors: Gerhard Loffler
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1994-04-20
Filing date: 1995-04-11
Publication date: 1995-10-25
Anticipated expiration: 2015-04-11
Also published as: GB2288669B; DE4413773C2; GB9507549D0; DE4413773A1

Description

dh 2288669 1 Method of controlling the imaging of a printing forme The

invention relates to a method of controlling the imaging of a printing forme, a method which assesses the quality of the plate exposure by evaluating control patches of an imaged plate produced on a printing material.

In order to control visually and metrologically the quality of a print produced on a printing material) print control strips including control patches of an imaged plate suitable for visually monitoring the plate imaging are produced at the margin of a printing material. In DE 24 01 672 A1 and DE 24 26 840 A1 such control elements are described. The control patches comprise fine line structures by means of which an operator may control as to whether the plates for the-print job have been imaged i.e. copied accurately and uniformly by locating the nontransferred graduations of the lines differing in thickness.. Furthermore, the patches may feature small dotted patterns used to control in different area-coverage regions the transfer of highlight dots onto the printing material; given a smooth transfer, certain patches appear in the printed image.

A disadvantage is the fact that the visual evaluation performed by an operator is subjective and depends on the attention and experience of said person. It is not possible to make a quantitative statement in view of the imaging quality of the printing forme.

Another disadvantage is that the graduations not to be transferred which, for example, depend on the resolution of the printing plate and on the fact as to whether a Positive or a negative copying technique is applied so that, when performing a visual control, confusion is likely to arise.

1 It is the object of the invention to provide a method which makes it possible to control the imaging of printing formes exactly and objectively.

According to the invention the object is achieved in that control patches of an imaged printing forme produced on a printing material generate image signals by means of an image-detecting device, and in that an evaluation device for the image signals determines deviations from reference image signals with respect to the control patches of the imaged printing forme.

Due to the invention the result of the control is not at all subjectively influenced by a person responsible for the control. The control is effected quickly, accurately end reliably. The evaluation of the image signals may be computer-controlled permitting a numeric output of the control results in the form of length specifications for the resolution of a printing forme and the degree of the transfer of halftone values.

It is advantageous to produce image signals directly when the printing material is conveyed through the printing machine, and to emit a signal if a respective threshold of a deviation is exceeded.

The invention is to be explained in greater detail with reference to a specimen embodiment.

In an offset printing machine having four printing units, seen in conveying direction of the printing material, the image-detecting device is provided after the last printing unit and directed onto the printing material. Said image-detecting device is suited to detect the entire surface of the printing material.

3 - In each printing unit a print control strip having plate-exposure control patches is copied onto each printing plate. Said control patches may be conventional and standardized, or they may be especially suitable for evaluation by means of an image-detecting device. Said control patches are tranferred onto the printing material and detected by means of the image-detecting device. The actual image signals obtained from the control patches are supplied by an evaluation device in which they are compared with stored reference image signals for the plate-exposure control elements. Measuring signals representing the imaging quality of the printing plate are derived from the comparing signals. If a printing plate has not been accurately imaged and the comparing signal exceeds a given quantity, it is conceivable to emit an optical or acoustic signal causing the operator of the printing machine to exchange the respective plate:

The method may be applied irrespectively of the method with which the printing plate is imaged.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

1 C L A 1 M S Method of controlling the imaging of a printing forme, method with which. by means of a printing machine, control patches of an imaged printing forme are produced on a printing material and evaluated, characterized in that, by means of an image-detecting device, image signals are produced by the control patches of the imaged printing forme, and that with respect to the image signals an evaluation device determines deviations from reference image signals.

Claims

2. Method according to Claim 1 characterized in that the image signals are

produced while the printing material is conveyed through the printing machine. and that a signal is emitted if a respective threshold of a deviation is exceeded.

3.

A method of controlling the imaging of a printing forme as claimed in claim 1 and substantially as hereinbefore described.