Printing – Flexible-sheet-securing devices
Reexamination Certificate
1999-11-24
2003-02-18
Evanisko, Leslie J. (Department: 2854)
Printing
Flexible-sheet-securing devices
C101S378000
Reexamination Certificate
active
06520085
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for positioning and tensioning a cylinder dressing on a printing-machine cylinder, including both a leading end of a dressing and a trailing end of a dressing. The invention, furthermore, relates to a device for holding and tensioning a cylinder dressing on a printing-machine cylinder, the device having a first arm for holding a first end of a dressing, a second arm for holding a second end of the dressing, and a cam member rotatable for adjusting the first and second arms.
Such a method can be performed, for example, by the device described heretofore in the published German Patent Document DE 42 22 332 C2, the cylinder dressing being tensioned and relieved of tension simultaneously at the leading edge and trailing edge thereof due to the construction of this device. The cylinder dressing in the form of a rubber blanket can be displaced relative to the original position thereof on the jacket of a printing-machine cylinder. For this purpose, the rubber blanket is relieved of tension at the leading edge and the trailing edges thereof by an actuating drive, a toothed quadrant clamping being released at a tension spindle, and the latter being rotated an adjusting travel distance.
SUMMARY OF THE INVENTION
Proceeding from this state of the prior art, it is an object of the invention to provide an improved method for tensioning and positioning a cylinder dressing on a printing machine cylinder.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for positioning and tensioning a cylinder dressing on a printing-machine cylinder, wherein both a leading dressing end and a trailing dressing end of the cylinder dressing are tensioned, which comprises, in a first step, tensioning both dressing ends, and in a second step, relieving the tension in a first of the two dressing ends, while retensioning a second of the dressing ends.
In accordance with another mode of the method of the invention, the first of the two dressing ends is the leading dressing end, and the second of the two dressing ends is the trailing dressing end.
In accordance with a further mode, the method of the invention, comprises successively tensioning the dressing ends in the first step.
In accordance with an added mode, the method of the invention comprises initially tensioning the trailing dressing end, and subsequently tensioning the leading dressing end in the first step.
In accordance with an additional mode, the method of the invention comprises tensioning both of the dressing ends simultaneously in the first step.
In accordance with another aspect of the invention, there is provided a device for holding and tensioning a cylinder dressing on a printing-machine cylinder, the device having a first arm for holding a leading dressing end of the cylinder dressing, and a second arm for holding a trailing dressing end of the cylinder dressing, and a rotatable cam member for adjusting the first and second arms, comprising a first tension lever pivotable about a first rotary joint, and a second tension lever pivotable about a second rotary joint, the first arm being formed on the first tension lever, and the second arm being formed on the second tension lever.
In accordance with another feature of the invention, the tension levers are loaded by altogether at least one spring.
In accordance with a further feature of the invention, the first rotary joint and the second rotary joint are disposed coaxially with one another.
In accordance with an added feature of the invention, the rotary joints are disposed so as to be offset eccentrically relative to an axis of rotation of the printing-machine cylinder.
In accordance with an additional feature of the invention, at least one spring extends through the first rotary joint and through the second rotary joint.
In accordance with yet another feature of the invention, the at least one spring is a torsion bar spring.
In accordance with yet a further feature of the invention, the tension levers are formed as rockers, and each of the rockers has a first rocker arm for holding the cylinder dressing, and a second rocker arm actuatable by the cam member.
In accordance with yet an added feature of the invention, the device includes a respective roller engageable by the cam member being mounted rotatably in each of the second rocker arms.
In accordance with yet an additional feature of the invention, the tension levers, respectively, carry a clamping device for holding the cylinder dressing.
In accordance with a concomitant aspect of the invention, there is provided a printing machine having at least one device for positioning and tensioning a cylinder dressing having at least one of the foregoing features.
Thus, the method for positioning and tensioning a cylinder dressing on a printing-machine cylinder, which includes tensioning both a front or leading dressing end and a rear or trailing dressing end, is distinguished in that, in a first method step, the two dressing ends are tensioned and, in a second method step following the first method step, a first dressing end of the two dressing ends is relieved of tension or detensioned, and a second dressing end of the two dressing ends is retensioned.
The cylinder dressing can be displaced in circumferential direction on the circumferential surface of the cylinder in this simple way, in practice the first dressing end being pushed and the second dressing end being pulled in the tensioning direction of the second dressing end. In relation to the tension of the first dressing end achieved in the first method step, often only partial detensioning or relief of tension is necessary in the second method step. The detensioning of the first dressing end may commence either before the retensioning of the second dressing end or simultaneously therewith. In both cases, the second dressing end is retensioned during the detensioning of the first dressing end.
Certain cylinder dressings have to be tensioned, in practice, by pulling on both dressing ends in tensioning directions opposite to one another, so that the cylinder dressings can be tensioned so as to rest tautly on the cylinder. The need for tensioning these cylinder dressings at both ends is due to friction between the cylinder dressing and the supporting surface of the cylinder, this friction being comparable to rope friction and being capable of being overcome only by pulling on both ends.
The method according to the invention is based on the assumption that even cylinder dressings to be tensioned in this way can be displaced on the circumferential surface of the cylinder if displacement is preceded by tensioning at both ends. It is assumed that, during clamping, disruptive deformations of the cylinder dressing play a part, as well as the rope friction-like effect. Often permanent deformations become noticeable, particularly after lengthy use and the associated repeated clamping and removal of the cylinder dressing on and off the cylinder. Such deformations can be eliminated by taut tensioning at both ends which precedes displacement, so that the cylinder dressing can subsequently be displaced, and exactly positioned, on the circumferential surface of the cylinder more easily than has been assumed hitherto.
Preferably, a leading dressing end corresponds to the first dressing end and a trailing dressing end to the second dressing end, so that, in the second method step, the leading dressing end is at least partly detensioned, and the trailing dressing end is retensioned. By the leading or front dressing end there is meant that end which, when the printing-machine cylinder carrying the cylinder dressing rolls in operative contact with or on a further printing-machine cylinder, is guided first past the further printing-machine cylinder during each revolution. In the event that the printing-machine cylinder is a plate cylinder for applying a printing ink or a varnish to a print carrier and the other printing machine cylinder is an impression cylinder
Heiler Peter
Kropp Frank
Evanisko Leslie J.
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Lerner Herbert L.
Stemer Werner H.
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