Printing – Processes – Condition responsive
Reexamination Certificate
2001-07-11
2003-08-26
Nolan, Jr., Charles H. (Department: 2854)
Printing
Processes
Condition responsive
C101S171000, C101S181000, C101S211000, C101S483000
Reexamination Certificate
active
06609462
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method and a device for controlling a transfer register in a sheet-fed rotary printing machine.
Modern sheet-fed offset printing machines attain printing speeds of 15,000 and more sheets per hour and, based upon the dc-drives which are used, can be operated over a wide rotational-speed range.
Regardless of the printing speed, positional accuracy of color separations relative to one another is an essential precondition for achieving good printing quality. This positional accuracy is characterized by the transfer register.
For evaluation or assessment, a distinction is drawn between the circumferential and lateral directions. A faulty position of color separations relative to one another can have an effect upon the appearance of the print color, in particular, in multicolor half-tone, and upon sharpness of detail. In addition, ghosting phenomena can result from a succession of fluctuations in the transfer register during the printing process.
The transfer register is influenced by a great number of factors, which can be divided mainly into dynamic and static influences. In addition to printing speed, one of the most significant factors, the transfer of sheets from the paper-quiding cylinders, and sheet displacements in the grippers, which can be viewed as dynamic influences, there are yet many other speed-independent factors which include the position of color separations on the printing plates and the position of the plates on the plate cylinders. In addition, the temperature in the individual printing units, the subject, as well as the viscosity of the ink have an influence upon the transfer register.
In order to keep the transfer register constant, i.e., to avoid register differences, a great deal of effort is expended with regard to construction. For example, improving the rigidity of the gear train is a measure to be included therein. All the measures in this regard, in addition to the outlay for construction, have the further disadvantage that physical limits make a compensation measure inevitable. For example, each change in the printing speed from a basic rotational speed to continuous or production-printing rotational speed generally entails register differences. These are based mainly on three primary influencing factors.
First, because of the rotational speed-dependent load torque of the individual printing units, torsion, which depends upon the rotational speed, occurs in the mechanical drive train of the machine. Furthermore, changes in the pull-off or withdrawal forces on the sheets, and the change in the drive power caused by the heating of the individual printing units because of deformations in the gear train have an influence upon the transfer register. However, the influence of rapid changes, for example, of the rotational speed, is greatest with regard to ghosting.
In order to be able to correct the occurring register differences, remotely adjustable devices for register adjustment are provided in the individual printing units in modern printing machines. For the purpose of correcting in the circumferential direction, and in the lateral direction, and for making a diagonal adjustment, the plate cylinders, in particular, can be constructed so that they are remotely adjustable with respect to the blanket cylinders cooperating therewith.
The prior art discloses an automatic register measuring and control device of the firm Heidelberger Druckmaschinen AG of Heidelberg, Germany, having the designation CPC-42, referred to hereinafter as Autoregister, wherein, in each printing unit, measuring marks which describe the position of the color separation on the paper sheet are printed at the sheet edges. The register differences are then compensated for by the fact that, by using these printed register marks or the like, the register differences of the individual partial colors relative to one another are determined, and serve for calculating actuating commands for required register corrections, and the latter are used for adjusting. In order for the individual partial colors to come into coincidence again with the correct position, the position of the individual plate cylinders in the printing units is corrected, in particular for the circumferential and lateral register. Before the register marks can be read-in at the last printing unit, and existing register differences can be corrected by the Autoregister, some sheets have already been transported through the printing machine. In the case of a ten-color printing machine, 27 sheets have already been printed before the distances between the various marks have been read-in and processed.
It is precisely in the phases during which acceleration or braking of the printing machine takes place that the Autoregister control cannot react optimally because of the circumstances mentioned at the introduction hereto.
In order to counteract this problem, the published European Patent Document EP 0 513 284 B1 proposes that the dynamic states, i.e., acceleration and braking, be detected during the printing job by an acceleration detecting device and, at the same time, that the automatic register control be switched off.
In addition, the published German Patent Document DE 44 34 843 A1 discloses a control system which, by using previously determined empirical values, represents the speed-dependent changes in the transfer register of the individual printing units relative to one another, and deposits them in a family of characteristic curves. For each individual printing unit, one such characteristic curve is determined which specifies how large the correction to be performed in the circumferential register has to be in order just to correct the register difference in the circumferential direction caused by the printing unit under consideration. A great number of trials is required in order to determine such characteristic curves, which are then stored in a control system. The quality of the results, therefore, depends upon the quality of these stored characteristic curves and, in particular, upon the question as to the extent to which it is possible to describe complex reality in the manner of a model by using such a characteristic curve. Situations are easy to imagine wherein, nevertheless, rejects will accumulate to a considerable extent, because the characteristic curve does not exactly represent the behavior of the machine.
SUMMARY OF THE INVENTION
Starting from the aforementioned prior art, it is an object of the invention to provide a method and a device for controlling a transfer register in a sheet-fed rotary printing machine by which the number of rejects occurring during changes in the printing speed is considerably reduced and, at the same time, to aid the pressman in arriving more quickly at a good sheet.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of avoiding register differences during the operation of a printing machine having a plurality of individual printing units, which comprises counteracting, at least by circumferential register corrections, respective register differences in the individual printing units, determining the register differences for different printing speeds and storing them in a memory, and determining the various register differences at different printing speeds by an automatic register measuring and register control device and, in the event of changes in the printing speed, superimposing the previously determined magnitude of the register correction on an adjusted variable of the automatic register measuring and register control device.
In accordance with another mode, the method of the invention includes calculating in a central control device corrections dependent upon printing speed, which are required to compensate for register differences.
In accordance with a further mode, the method of the invention includes performing the calculation required to compensate for register differences based upon values which have been determined automatica
Heidelberger Druckmaschinen AG
Nolan, Jr. Charles H.
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