Printing – Processes
Reexamination Certificate
2000-02-07
2003-04-15
Eickholt, Eugene H. (Department: 2854)
Printing
Processes
C101S350500, C101S352010
Reexamination Certificate
active
06546869
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method of operating a printing machine, more particularly, a printing machine that includes a printing form or plate cylinder and an inking unit for inking the cylinder, the inking unit having at least one inking unit roller rotatably driven at a speed different from the peripheral speed of the printing form cylinder. The invention further relates to a printing machine for performing the aforementioned method, more particularly, a printing machine that includes a printing form or plate cylinder and an inking unit for inking the cylinder, the inking unit having at least one inking unit roller rotatably driven at a speed different from the peripheral speed of the printing form cylinder.
The published European Patent Document EP 0 813 963 A1 describes an offset printing device wherein ink applicator rollers are driven frictionally at differential speeds different from the peripheral speed of a form or plate cylinder by formlockingly or positively driven inking rollers, and it is possible for the formlockingly driven inking rollers to be changed over from a differential speed to a synchronous speed relative to the peripheral speed of the form cylinder, depending upon the subject and/or printing material to be processed. In this regard, it is noted that a formlocking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a forcelocking connection, which locks the elements together by force external to the elements.
Although the wear behavior of a dry planographic printing plate can be improved thereby in cases wherein no contamination or only slight contamination occurs, no different operating states of the inking unit are taken into consideration at the time when a shift or change-over is made to the synchronous speed.
For example, no consideration is given as to whether the inking rollers are rotating at the synchronous speed or at the differential speed that differs from the plate-cylinder speed, before ink runs into the inking unit or after an inking-unit cleaning.
Consequently, the disadvantages described hereinbelow result.
If the inking unit of the offset printing device is to be cleaned, it is possible for the ink applicator rollers to rest on the plate cylinder during the cleaning, so that the printing plate is indirectly cleaned simultaneously via the inking unit. Cleaning can be performed in a number of washing cycles, respectively, including feeding washing fluid into the inking unit, and subsequent doctoring of the washing fluid/printing ink mixture. The inking unit and the printing plate or form increasingly cleaner from washing cycle to washing cycle, as a result of which, rubber-covered inking-unit rollers are subjected to rapidly increasing wear because of the vanishing lubricating action of the printing ink between the inking unit rollers. Because the formlockingly or positively driven inking rollers of the offset printing device belonging to the prior art rotate at the differential speed during the cleaning, each ink applicator roller is subjected to increased abrasion that is virtually dry at the end of the cleaning, both at the first slippage point thereof formed with the plate cylinder, and at the second slippage point thereof formed with the inking roller driving the ink applicator roller frictionally. When special inks and the like specific to a printing job are used, inking units have to be cleaned several times a day, so that the wear stresses associated with each cleaning operation add up and, after a comparatively short service life, make it necessary to replace the worn inking-unit roller.
If ink is to be introduced into the inking unit of this offset printing device, it is conceivable to bring the ink applicator rollers thereof into contact with the printing plate only after the infeeding of the ink, however, in this case, the problem of dry abrasion of rubber-covered rollers in the inking unit likewise arises if a number of the formlockingly or positively driven inking rollers rotate at differential speeds which differ in amount relative to one another. If the inking unit runs for a given time without printing ink, and therefore nonlubricated, before entry of the ink, the formlockingly or positively driven inking rollers gradually wear away the rubber-covered rollers arranged therebetween in the roller train of the inking unit. The two slippage points are formed, in this case, by the respective rubber-covered roller together with a first and a second adjacent roller engaging the rubber-covered roller. The adjacent rollers can be directly the two inking rollers driven formlockingly or positively at different differential speeds, or rollers arranged between the formlockingly or positively driven inking rollers and the rubber-covered inking roller.
In a further offset printing device described in the published German Patent Document DE 196 25 020 A1, the problems described hereinbefore and caused by inking unit rollers stripping or running blind occur in the same way.
SUMMARY OF THE INVENTION
It is thus an object of the invention to provide an improved method for low-wear operation of a printing machine and to provide a printing machine by which the low-wear operation method is performed.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of operating a printing machine including a printing form cylinder and an inking unit for inking the cylinder, the inking unit having at least one inking unit roller rotatably driven at a differential speed different from the peripheral speed of the printing form cylinder, which comprises rotatably driving the at least one inking unit roller at the differential speed and at a relative speed that is different from the peripheral speed of the printing form cylinder, in time-dependence upon various operating states of the inking unit.
In accordance with another mode, the method of the invention includes driving the inking unit roller at the differential speed and at a synchronized speed in time-dependence upon various operating states of the inking unit.
In accordance with a further mode, the method of the invention includes driving the inking unit roller at the differential speed in a first operating state and at the synchronized speed in a second operating state, depending upon the ink content of the inking unit, which is different in the respective operating states.
In accordance with an added mode, the method of the invention includes driving the inking unit roller at the synchronized speed when the inking unit is running virtually without ink, and at the differential speed when the inking unit is running with ink.
In accordance with an additional mode, the method of the invention includes driving the inking unit roller at the differential speed and at a different differential speed in time-dependence upon the various operating states of the inking unit.
In accordance with yet another mode, the method of the invention includes driving the inking unit roller at the differential speed in a first operating state, and at the different differential speed in a second operating state, depending upon the ink content of the inking unit, which is different in the respective operating states.
In accordance with yet a further mode, the method of the invention includes driving the inking unit roller at the differential speed when the inking unit is running with ink, and driving the inking unit roller at the different differential speed when the inking unit is running virtually without ink.
In accordance with yet an added mode, the method of the invention includes changing-over the peripheral speed of the. inking unit roller in time-dependence upon an ink infeed into the inking unit.
In accordance with yet an additional mode, the method of the invention includes changing-over the peripheral speed of the inking unit roller in time-dependence upon a cleaning of the inking unit.
In accordance with a second aspect of the invention,
Eltner Bruno
Möller Bernd
Eickholt Eugene H.
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Mayback Gregory L.
Stemer Werner H.
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