The invention relates to an apparatus for guiding a print carrier, as well as a printing unit in a rotary printing machine having the apparatus. Throw-on and throw-off guide elements and guiding elements which can be adjusted relative to the former are provided for exchanging a print carrier, especially a printing plate or printing film, that is detachably held on a cylinder of a rotary printing machine.
German Patent DE 44 14 443 C1 has disclosed an apparatus for guiding a print carrier. A print carrier is guided to or away from a plate cylinder of a rotary printing machine with that apparatus. For that purpose, guide elements are disposed axially parallel to the plate cylinder and can be positioned through the use of an actuating mechanism. Two groups of guide elements are provided. In each case, one group is used as guide rollers for inserting the plate in order to feed-in the print carrier at a defined distance from the surface of the plate cylinder. The other group is thrown-off as a guide roller for plate ejection.
The respective guide roller for the plate ejection can be set at a defined distance from the surface of the plate cylinder in order to guide the print carrier out. The guide roller is thrown off for the plate insertion.
When unloading a used printing form provided with ink, be it a printing plate or a printing film, rings of the pressure roll are soiled by ink from the printing plate. When a new printing plate is clamped in, that ink is transferred to the unimaged printing plate by the ink-smeared rings. Due to the ink soiling, it is possible for imaging faults, disruptions or changes during the imaging of the printing plate to occur in directly imaging rotary printing machines. That problem is inherent in all directly imaging rotary printing machines with exchangeable printing plates.
Printing problems can likewise occur in machines with CTP and process-less printing plates or printing films. Those problems occur if ink from the rollers gets onto the printing plate, when the plate or the film is being fed in. The ink has a detrimental influence on the imaging behavior of the respectively soiled zones during the imaging, for example through the use of a laser head, as compared with unsoiled zones.
It is accordingly an object of the invention to provide an apparatus for guiding a print carrier and a printing unit in a rotary printing machine having the apparatus, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which avoid imaging faults in directly imaging rotary printing machines resulting from changing a print carrier.
With the foregoing and other objects in view there is provided, in accordance with the invention, in a rotary printing machine having a printing unit with a form cylinder, an apparatus for guiding a print carrier when feeding the print carrier to and guiding the print carrier away from the form cylinder. The apparatus comprises guide elements axially parallel to the form cylinder for assisting in feeding-in and pressing-on the print carrier. The guide elements are disposed in two groups. One of the groups of guide elements serves to pull-in the print carrier and the other of the groups of guide elements serves to remove the print carrier from the printing unit. Throw-on elements keep the guide elements from making contact with the print carrier during exchanging of the print carrier.
The advantages of the apparatus according to the invention can primarily be seen in the fact that when removing the respective print carrier, be it a printing plate or a printing film, contact between the inked print-carrier surface and the respective new print carrier, either printing plate or printing film, is prevented. Therefore, imaging faults resulting from handling can be ruled out in directly imaging rotary printing machines. The guide elements for the new print carrier to be fed in are effectively protected against any transfer of soiling from the preceding removal operation of the preceding printing form from the printing unit of the rotary printing machine. This is accomplished by constructing the throw-on elements as rotationally symmetrical bodies which can be pivoted or moved or which have a size that can be changed, in each case contacting the surfaces of the print carrier to be exchanged.
In accordance with another feature of the invention, the throw-on elements can be varied in terms of their position, their shape and their size in relation to the respective guide elements for a new print carrier to be fed in, be it a printing plate or printing film. The throw-on elements can be constructed to be pivotable in relation to the guide elements, they can be movable or their size relative to the latter can be changed. In particular, a contact zone between peripheral surfaces of the throw-on elements and the printing form to be guided away may be defined exactly, by changing the size in the circumferential direction. In that way, guide elements having a small diameter or being placed in a lower plane are effectively protected against any contact with the soiled surface of the printing form to be guided away.
In accordance with a further feature of the invention, the throw-on elements which have a soiled surface from the preceding operations are moved out of an active range of the guide elements contacting the fresh and printed printing form both before and during the action of feeding in a fresh printing form for imaging in the rotating system. For this purpose, the throw-on elements can either be pivoted away from the contact plane of the guide elements with the surface of the printing form to be fed in, can be moved away or removed from a range of engagement of the guide elements with the print-carrier surface through the use of a change in size.
In accordance with an added feature of the invention, a relative position between the peripheral surfaces of the guide elements and those of the throw-on elements can be changed by an actuating travel xcex94h through the use of an actuating cylinder. In this case, the actuating travel xcex94h can be preselected in such a way that when the throw-on elements make contact with the surface of the print carrier, the guide elements are located at a sufficient safety margin with respect to soiling from the soiled print-carrier surface.
In accordance with an additional feature of the invention, the movable throw-on elements may be connected to one another in an articulated manner through the use of coupling elements and coupling rods, for example on a base plate which rotatably accommodates the guide elements for the new printing form. In this case, the movable throw-on elements which can be actuated in this way are spaced apart from one another, through the use of an actuating cylinder to which a pressure medium can be applied. This is done in such a way that the throw-on elements support the printing plate to be removed from the printing unit of the rotary printing machine uniformly over the width of the printing unit. This results in no regions hanging down in the extent of the width of the print medium to be removed from the printing unit. Such regions could touch guide elements positioned underneath and, in that way, an undesired transfer of ink could take place. The throw-on elements, which are connected to one another in an articulated manner by the coupling elements and coupling rods, may be moved from an extended position into a retracted position and vice versa by applying pressure to the actuating cylinder.
In accordance with yet another feature of the invention, in the extended printing position of the throw-on elements, their peripheral surfaces project by an amount xcex94h beyond the peripheral surfaces of the guide elements. In addition to extending or pivoting the throw-on elements in relation to guide elements which are disposed in a stationary position for a print carrier to be fed in, throw-on surfaces to which pressure medium can be applied can be accommodated on a carrier that accommodates stationary guide elements. The throw-on elements to which pressure medium is applied can be connected directly to a cavity containing pressure medium through an opening and can be acted on directly through that cavity. It is equally possible to bring the throw-on elements into a position having a diameter that exceeds the peripheral surface of the carrier accommodating them, through contact surfaces constructed as a throw-on element, by using a plunger to which pressure medium can be applied.
In accordance with yet a further feature of the invention, a form cylinder, which accommodates a print carrier in the form of a printing plate or a printing film, can be associated with a carrier wheel having a circumferential position that can be influenced and a periphery which accommodates a group of guide elements in one segment and a group of throw-on elements in a further segment.
In accordance with yet an added feature of the invention, a guide element is accommodated in an articulated manner between two fixed bearings and is to be thrown onto the peripheral surface of the plate cylinder by an actuating cylinder to which a pressure medium can be applied. In this structural variant, the throw-on element remains in a fixed position, since it is associated with a fixed bearing. However, through the use of the actuating cylinder, which in turn is accommodated on a fixed bearing, the guide element can be thrown onto the peripheral surface of the form cylinder of a printing unit of a rotary printing machine.
With the objects of the invention in view, there is also provided, in a rotary printing machine, a printing unit, comprising a form cylinder, and an apparatus for guiding a print carrier when feeding the print carrier to and guiding the print carrier away from the form cylinder. The apparatus has guide elements disposed axially parallel to the form cylinder for assisting in feeding-in and pressing-on the print carrier. The guide elements are disposed in two groups. One of the groups of guide elements serves to pull-in the print carrier and the other of the groups of guide elements serves to remove the print carrier from the printing unit. The apparatus has throw-on elements for keeping the guide elements from making contact with the print carrier during exchanging of the print carrier.
The apparatus according to the invention may be provided on a printing unit of a directly imaging rotary printing machine, with laser-head units directly imaging the printing forms being provided in the printing units of such rotary printing machines. These units image the print carriers on the basis of imaging information stored in an RIP. The higher the surface quality of the printing forms to be fed in, the more accurate imaging may be achieved in the directly imaging rotary printing machine.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as, embodied in an apparatus for guiding a print carrier, as well as a printing unit in a rotary printing machine having the apparatus, it is nevertheless not intended to be limited to the details shown.
Various modifications and structural changes may be made in the invention without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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