Abstract:
A damping unit for a press has means for applying a damping solution to a printing form and means for setting the quantity of damping solution applied. At least one sensor is provided for registering the quantity of damping solution actually applied to the printing form. By means of a comparison with a predefined quantity of damping solution, the quantity of damping solution on the printing form can be regulated.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to printing devices, and more particularly to a damping unit for a printing press.  
       BACKGROUND OF THE INVENTION  
       [0002]     In planographic printing processes, it is generally known to wet the non-printing points of a printing form with damping solution and to wet the printing points with ink. The metering of the damping solution is controlled by the control desk. In the case of film damping units, the rotational speed of the damping solution distributor is driven and the quantity of damping solution across the web width is controlled manually by means of pressure changes between dip roll and damping solution distributor. In the case of nozzles and centrifugal damping units, the quantity of damping solution can be controlled via the spraying frequency of the nozzles or via the valve opening in the case of turbo damping units.  
         [0003]     In the case of controlled metering of the quantity of damping solution, it is disadvantageous that erroneous settings can occur.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     It is an object of the invention to improve the metering of the quantity of damping solution on a printing form.  
         [0005]     In a damping unit according to the invention, the quantity of damping solution on the printing plate is advantageously regulated. Moreover, a damping unit according to the invention is advantageously self-teaching and compensates automatically for changes on the roll coatings as a result of swelling or shrinkage.  
         [0006]     When starting up a new print job, the optimal settings can be stored, and, during the next such job, can be read back again into the control/regulating device of the damping unit as presetting data.  
         [0007]     Furthermore, the laborious determination of what is known as a “damping run-up curve” for different materials can be dispensed with, since the rotational speed of the damping unit and, likewise, the imprint widths of the dip roll can be regulated via a control signal of the damping unit according to the invention.  
         [0008]     Moreover, with a damping unit according to the invention, smearing, scumming and color build-up can be detected in good time and therefore the wastage can advantageously be reduced.  
         [0009]     Preferred embodiments of the invention are described in greater detail below with reference to the schematic drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a film damping unit in an embodiment according to the invention;  
         [0011]      FIG. 2  shows adjusting devices of the film damping unit;  
         [0012]      FIG. 3  shows a spray damping unit in another embodiment according to the invention; and  
         [0013]      FIG. 4  shows a centrifugal damping unit in yet another embodiment according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     In  FIG. 1 , the principle according to the invention is applied to an embodiment using a film damping unit, illustrated as a detail from a press is a plate cylinder  1 , which normally interacts with a transfer cylinder. On the plate cylinder  1  there is a printing form, which is provided with ink-accepting and ink-repelling regions. A damping solution is applied to the ink-repelling regions. In order to measure the damping solution layer thickness, a sensor  2  is provided, which is operatively connected to a control/regulating device  3 . A value of the damping solution layer thickness or quantity can be predefined in the control and regulating device  3 .  
         [0015]     Since the quantity of damping solution which is applied to the plate cylinder  1  depends firstly on the pressure between a dip roll  9  and a damping solution distributor  8  and on the oblique adjustment of the dip roll with respect to the damping solution distributor and on the damping solution distributor speed, the predefined value  4  results in a set point for the pressure between the dip roll  9  and damping solution distributor, a set point for the oblique adjustment of the dip roll with respect to the damping solution distributor and a set point for the damping solution distributor speed. From the signal from the sensor  2 , the control and regulating device  3  determines the respective actual values of the pressure between the dip roll and damping solution distributor, the actual value of the oblique adjustment of the dip roll and the damping solution distributor speed. Following a comparison between set points and actual values, the deviations determined are readjusted by means of appropriate regulating devices  5 .  
         [0016]     In order to adjust the pressure between the dip roll  9  and the damping solution distributor roll  8 , two motors  6   a, b  are provided, which are able to adjust the roll mountings, preferably via spindles. A further motor  6   c  is provided for the oblique adjustment of the dip roll, and a motor  6   d  is driven in order to regulate the damping solution distributor speed. The achievement of the predefined value  4  is manifested by the production of what is known as a good sheet. The latter has the desired print quality and the values for the control variables a, b, c and d adjusted for this purpose can be stored and later read back again into the control and regulating device  3  for the production of a similar job. Instead of a single sensor  2 , a plurality of sensors  2  can also be provided, which are arranged distributed over the width of the printing form. The result is an evaluation of different regions of the printing form, and it is possible to regulate the corresponding regions differently as well.  
         [0017]     In order to regulate to the predefined value  4 , each control variable a, b, c, d can be regulated on its own or in conjunction with one or more others.  
         [0018]      FIG. 2  illustrates the possible adjustments of the film damping unit in a side view. The dip roll  9  applies the damping solution to a damping solution distributor roll  8 , which applies the damping solution to the printing form on the plate cylinder  1  via an applicator roll  7 . In order to adjust the pressure between the dip roll  9  and the distributor roll  8 , adjusting motors  6   a, b  are provided, which are able to adjust the position of the roll mountings, preferably via spindles. For the purpose of adjusting the dip roll  9  obliquely with respect to the distributor roll  8 , an adjusting motor  6   c  is provided, which likewise acts on the mounting of the dip roll  9 , preferably via a spindle drive.  
         [0019]      FIG. 3  illustrates an application of the principle according to the invention in an embodiment that uses a spray damping unit. In the case of a spray damping unit, the damping solution is sprayed via a spraying bar having a plurality of nozzles onto a damping solution distributor roll, which transfers the damping solution to the plate cylinder via a damping solution applicator roll. The quantity of damping solution may be influenced by the cycle frequency  10  and the cycle period  11  of the spraying. Furthermore, influence can also be exerted on the damping solution layer thickness via the damping solution distributor roll rotational speed  12  and the damping solution applicator roll rotational speed  13 . As in the preceding exemplary embodiment, a sensor  2  is also provided here, which passes the actual value of the damping solution layer thickness on to a control/regulating device  3 . The control and regulating device  3  breaks down the actual value into an actual value of the cycle frequency  10 , cycle period  11 , damping solution distributor rotational speed  12  and speed of the damping solution applicator roll  13 . These actual values are compared with the associated set points i, f, g, h, which result from the predefined value of the quantity of damping solution. Following a comparison between the set points and the actual values, the corresponding deviations are readjusted. As soon as the first “good sheet” is produced, the ideal settings have been reached and can be stored. These values are read back into the control and regulating device  3  again for the next similar job and used as predefined values for the various settings.  
         [0020]     An embodiment of a centrifugal damping unit according to the invention is illustrated in  FIG. 4 . In the case of centrifugal damping units, the damping solution is thrown onto a damping solution distributor without contact by a rotor, or directly onto the plate cylinder  1 . Adjustable shields are provided in order to meter the quantity of damping solution. It is also possible for the damping solution distributor rotational speed or the rotational speed of the damping solution applicator roll to be used for metering. As in the preceding exemplary embodiments, a sensor  2  determines the damping solution layer thickness on the plate cylinder  1 , and passes it on to a control and regulating device  3 . The control and regulating device  3  breaks down the actual value of the damping solution layer thickness into an actual value for the shield position, damping solution distributor rotational speed and the speed of the damping solution applicator roll. A predefined value for the quantity of damping solution can be entered into the control and regulating device, which is broken down into set points i, j, k for the shield position, damping solution distributor rotational speed and damping solution applicator roll rotational speed. Following a comparison between the individual set points and actual values, the various settings can be readjusted by controllers  5   i, j, k.  As soon as the first good sheet is produced, the ideal settings have been reached and can be stored in a memory in order later to be read back in a manner analogous to the preceding exemplary embodiments.