Printing – Processes – Position or alignment
Reexamination Certificate
2003-05-21
2004-11-02
Eickholt, Eugene H. (Department: 2854)
Printing
Processes
Position or alignment
C101S216000, C101S228000, C101S247000, C101S248000, C226S031000, C226S044000, C226S092000, C226S195000
Reexamination Certificate
active
06810812
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method for regulating a web tension. The web is stretched between a pair of cylinders. The two cylinders interact with each other through the web.
BACKGROUND OF THE INVENTION
A registration-maintaining drive mechanism for a rotary printing press is known from EP 0 951 993 A1. A longitudinal stretching of the web of material to be imprinted is determined from the web tension values and operating values of the drive mechanisms. This longitudinal stretching is compensated for by adjusting the circumferential registration at the cylinders or the registration rollers.
Printing groups are disclosed in DE 42 11 379 A1, whose rubber blanket cylinders are seated in adjustable eccentric bushings. The contacting of the rubber blanket cylinders is varied by pivoting around the first eccentric axis. A variation of the printing width of an ink application roller with respect to the screen roller is provided by pivoting around the second eccentric axis.
SUMMARY OF THE INVENTION
The object of the present invention is directed to providing a method for regulating a web tension.
In accordance with the present invention, this object is attained by stretching the web between a pair of cylinders that interact with each other via the web. A change in the distance between the two cylinders is used to regulate the web tension. An actual value of a parameter that defines the relationship of the tension in the web before and after the cylinders is measured and is compared with a set point. A deviation between the two is used to change the distance between the cylinders.
The advantages to be gained by the method of the present invention consist, in particular, in that the printing groups, or print units, can be regulated in a simple manner via the existing tensile stress, or tension, of the web, for example the web of material to be imprinted or the paper web. This is achieved by changing the pressure feed adjustment between the cylinders which interact with each other via the web. In an advantageous manner this is accomplished with “rubber against rubber pressure” of the two interacting transfer cylinders of a printing group.
The conveying behavior of a web through a printing press is subjected to many influences, such as, for example, the tension/stretching characteristics of the respective paper, and therefore the prevailing tension, the instantaneous moisture of the web, the sensitivity of the web to moisture, the penetration behavior of moisture into the web, the position of the roll while being produced on the reel spool which, for example, finds its expression in variations of the winding hardness, and location-dependent variations in the modulus of elasticity of the web. Besides this, the conveying behavior of a web is also a function of the dressing and of the contact pressure.
By utilization of the method in accordance with the present invention, it is possible, in an advantageous manner, to affect the conveying behavior of the web through one or several printing groups of the printing press and to regulate it without requiring a change of rubber blankets to ones of different thickness, or requiring a change in running the process, for example a change of dampening. A change in the tension of the web can be counteracted during the printing process by changing the conveying behavior. The employment of different rubber blankets or different types of paper is also possible, since by use of the method of the present invention, the conveying behavior and the print quality can be changed by changing the distance rather than by changing the thickness of the rubber blankets.
In a reversed method, it is possible to use rubber blankets with different conveying behavior, of different quality and/or of different thickness, wherein the desired web tension, or graduation of the web tension between the printing groups can be automatically maintained almost constant.
Rubber blankets from certain manufacturers act in a “negatively conveying manner”, for example, the web is braked. Rubber blankets from other manufacturers act in a “positively conveying manner”, the web is “pushed along” in addition to it undergoing an unwinding at the nip location.
The conveying behavior of the web is also a function of the contact pressure between the rubber blankets and the paper web.
In a preferred embodiment of the present invention, the transfer cylinders are driven in pairs by their own drive mechanism. The forme cylinders interacting with the transfer cylinders, as well as with ink and dampening units, are embodied to be individually driven and are only electrically synchronized with the transfer cylinders. The advantages resulting from this are, among others, the avoidance of gear tooth play, which occurs in case of a mechanical coupling of the transfer and forme cylinders, for example, and an almost torsion-proof and angle-synchronous driving of the forme cylinders with respect to the transfer cylinders. Further than that, fluctuations of torque, caused for example by distributing rollers or siphon ink units, are damped by the separate drive mechanisms for the forme cylinders, together with their associated ink and dampening units, and are not transmitted to the transfer cylinders. This results in a printing process which is undisturbed to a great extent.
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Eickholt Eugene H.
Jones Tullar & Cooper PC
Koenig & Bauer Aktiengesellschaft
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