Electrophotography – Document handling – Copy
Patent
1997-09-24
2000-04-25
Lee, S.
Electrophotography
Document handling
Copy
399400, G03G 1500
Patent
active
060554088
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a device for the positionally exact synchronization of the parallel course of recording medium webs in an electrographic printer device.
2. Description of the Related Art
An electrographic printer device wherein two recording medium webs arranged parallel are simultaneously moved through the printer and printed is disclosed, for example, by published International Patent application WO 94/27193. In such a printer device and other paper-processing systems wherein two parallel paper webs pass through successive function units with friction or positive drive, the drive of the paper webs is a particular problem. In order to avoid malfunctions, thus, a parallel, synchronous paper course must be guaranteed.
DESCRIPTION OF THE PROBLEM
The following is to be noted or, respectively, the following problems generally occur when synchronously conveying a paper web through a plurality of function units of a printer device: In order to achieve a prescribed registration precision, the printing format must be aligned relative to the paper form when printing.
Tensile forces occur in the web upon passage of the web through the printer. These are partly unavoidable, for example due to friction. On the other hand, tensile forces are intentionally introduced into the web in order to stabilize the paper running.
The tensile forces in the paper vary during printing.
The drives drive the web opposite the influence of the tensile forces (described below).
The paper web shrinks when it is heated, namely dependent on the paper grade (which determines, for example, the water content) and the extent of heating. Upon passage through a standard type thermal fixing station, for example, the shrinkage in the web direction lies on the order of magnitude of 0.06%.
The advance feed holes of the paper webs are subject to manufacturing tolerances. These amount to up to 0.12% of the rated dimension.
DISCUSSION OF THE VARIOUS OPERATING MODES
Different conveying principles are applied for driving the paper webs, for example in continuous printers. These are:
The drive of the paper webs by friction usually ensues in roller nips or via friction roller drives. What is thereby particularly critical is the drive in the roller nip (in other words, the fixing gap) between the fixing and pressure rollers of a thermal pressure fixing station.
A friction drive conveys a web length per a time interval. However, the slippage, which occurs on principle in any friction drive, varies dependent on force and friction relationships. Slippage means that there is no fixed transmission ratio between the driving part and the driven part, and the driven part lags behind the driving part to a greater or lesser extent. Given drive in the roller nip of, for example, a fixing station, the paper web is slower by the slippage than the surface speed of the drive roller. Given a constant drive motor speed, thus, the speed of the driven paper web changes due to influences of force and friction.
The drive of paper webs by positive lock usually ensues via paper-conveying caterpillars or pin wheels that engage into advance feed holes of the paper. What is meant here by a positive drive is also a drive that is in fact a friction drive in mechanical terms but is controlled, for example, by electronic means to the conveying of form elements. Such a drive, accordingly, automatically compensates for differing slippage and behaves like a positive drive with respect to the web speed. Form elements are repeating, detectable features involving the paper web. These, for example, can be: advance feed holes, printing marks, folds, perforations, or labels.
A positive drive conveys a defined plurality of form elements (for example, links of a chain, or advance feed holes in the paper web) per time interval. Due to various influences, the advance feed holes can have different spacings from one another (due to perforation tolerances, or paper shrinkage). Tolerances in the hole spacing below an allowa
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Mayer, "Prazise gesteuerte Schrittmotoren ermoglichen Ruckseitendruck", F&M Feinwerktechnik & Messtechnik, vol. 100, No. 8, Aug. 1992, Munich, pp. 339-343.
Creutzmann Edmund
Eckardt Andreas
Kopp Walter
Silbersack Martin
Winter Hans
Lee S.
Oce Printing Systems GmbH
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