Abstract:
A method for driving rollers of a printing unit of a printing press, includes driving at least two of the rollers at different speeds for transferring liquid. A change in the torque on one of the rollers is determined. A drive for at least one of the rollers is set in dependence on the change in the torque.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a method for driving rollers of a printing unit of a printing press, wherein at least two rollers are driven at different speeds for transferring liquid.  
         [0003]     A printing unit of a wet offset printing press has an inking unit and a dampening unit provided with transfer and applicator rollers for printing ink and dampening solution. German Published, Non-prosecuted Patent Application DE 196 45 169 A1 discloses a printing unit having an inking unit roller train and a dampening unit roller train. In that device, besides a dampening solution ductor, all the rollers have a drive connection to a plate cylinder and a rubber-covered cylinder. The dampening solution ductor has a separate controllable-speed drive. A spraying device for cleaning fluid and a doctor device are provided in order to clean all of the rollers and cylinders. When cleaning the cylinders and rollers, initially all of the rollers of the inking unit roller train are cleaned. Thereafter, a dampening solution applicator roller is coupled to the inking unit roller train by a bridging roller. Then, with the spraying device and the doctor device activated, the dampening solution ductor is operated for a limited time at a peripheral speed which is above the peripheral speed that is usual during the printing operation. At the same time, the machine speed of the printing unit is set to a rotational speed at which the peripheral speed of the dampening solution applicator roller driven by the plate cylinder is synchronized with the peripheral speed of the dampening solution ductor. That is intended to ensure that, during the cleaning of the rollers and the cylinders, external friction is maintained and a decrease in the transferable peripheral force in the roller pairing is avoided.  
         [0004]     Due to the required synchronism of the dampening solution ductor with the dampening solution applicator roller, the drive of the dampening solution ductor must be controlled as a function of the difference in the rotational angle or rotational speed between the rollers. Rotary encoders are suitable as detectors for the measurement of the actual value of the peripheral speeds.  
       SUMMARY OF THE INVENTION  
       [0005]     It is accordingly an object of the invention to provide a method for driving rollers of a printing unit of a printing press, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and which affords flexible control of various operating procedures.  
         [0006]     With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for driving rollers of a printing unit of a printing press. The method comprises driving at least two of the rollers at different speeds for transferring liquid. A change in the torque on one of the rollers is determined. A drive for at least one of the rollers is set depending upon the change in the torque.  
         [0007]     In accordance with another mode of the inventive method, the printing unit is an offset printing unit having at least one dampening solution transfer roller and a dampening solution dip roller. The method includes, during a cleaning of inking unit and dampening unit rollers, driving the dampening solution transfer roller, together with inking unit rollers, by a first motor. The dampening solution dip roller is driven by a second motor. The torque on the dampening solution dip roller is determined.  
         [0008]     In accordance with a further mode, the method includes operating the second motor in braking operation.  
         [0009]     In accordance with an added mode, the method further includes, during braking with the second motor, measuring electrical variables, and determining a change in the torque from the measurement of the electrical variables.  
         [0010]     In accordance with an additional mode, the method further includes predetermining a limiting value for the torque. A signal for ending the cleaning operation is derived if the limiting value is exceeded.  
         [0011]     In accordance with yet another mode, the method further includes, for cleaning, feeding a liquid cleaning agent to the rollers of the inking unit or the dampening unit under pressure through a spray pipe. A limiting value for the torque is predetermined and a signal for beginning to supply the cleaning agent is derived, if the limiting value for the torque is exceeded.  
         [0012]     In accordance with yet a further mode, the method further Includes predetermining a limiting value for the torque, and, if the limiting value is exceeded, changing the rotational speed of one of the rollers.  
         [0013]     In accordance with yet an added mode, the method further includes throwing the two rollers revolving at different speeds onto one another. A limiting value for the torque as a function of the material of the covers of the two rollers is predetermined.  
         [0014]     In accordance with yet an additional mode, the method further includes introducing into a control device characteristic numbers typifying the rollers. The limiting value is derived with the aid of the characteristic numbers.  
         [0015]     In accordance with another mode, the method further includes reading out identifiers typifying the rollers and entering them into a control device. The limiting value is derived with the aid of the identifiers.  
         [0016]     In accordance with a further mode, the method further includes predetermining a limiting value for the torque. A time period during which the limiting value is exceeded is registered.  
         [0017]     In accordance with an alternate mode, the method further includes determining the change in the torque as a function of machine parameters.  
         [0018]     In accordance with another alternate mode, the method further includes determining the change in the torque as a function of the temperature in the printing unit.  
         [0019]     In accordance with a further alternate mode, the method further includes determining the change in the torque as a function of a system voltage of motors driving the rollers.  
         [0020]     In accordance with an added mode, the method further includes throwing the two rollers revolving at different speeds onto one another. The drive for at least one of the rollers is set so that the friction between the two rollers is changed.  
         [0021]     In accordance with an additional mode, the method further includes adding a fluid into the contact region of the two thrown-on rollers for reducing friction therebetween.  
         [0022]     In accordance with an alternate mode, the method further includes reducing the pressure between the thrown-on rollers so as to reduce the friction therebetween.  
         [0023]     In accordance with another alternate mode, the method further includes reducing the absolute speed of the thrown-on rollers so as to reduce the friction therebetween.  
         [0024]     In accordance with yet another mode, the method further includes increasing the rotational speed of one of the thrown-on rollers until the torque has reached a predefined value.  
         [0025]     In accordance with a concomitant mode, the method further includes providing an offset printing unit having inking and dampening unit rollers and a cleaning configuration for the rollers. A signal for deaeration of lines containing a supply of liquid cleaning agent in the offset printing unit is generated by the change in the torque.  
         [0026]     Thus, according to the invention, the torque of at least one of the rollers is monitored. A drive for this roller or a roller having a drive connection to this roller is set depending upon the torque curve or course of the roller. The drive is set in such a manner that a defined slippage is produced between the driven roller and one or more thrown-on rollers. In order to produce the slippage, a specific moment is required when the rollers have a damp surface. This moment can be applied with a drive motor which is operated with a braking current. If the friction between the rollers increases, the braking torque to be applied by the drive motor then rises. When the rollers are wet or damp, a drive moment is required which reduces with increasing drying of the roller surfaces, because of the increasing frictional force, until ultimately a braking moment has to be applied in order to attain a desired slippage.  
         [0027]     It is advantageous to limit the braking moment of a drive to a predefined value. The instant the drive exceeds the limiting value, a signal is generated in a control device for the operation of the printing press. In particular, by the use of the signal, a cleaning cycle for the rollers can be ended or the pressure between rollers can be changed through an actuator. It is also possible for the supply of cleaning agent to be controlled by evaluating the braking moment in the control device. Therefore, the quality of the cleaning operation is improved, the cleaning time is shortened and the consumption of cleaning agent is reduced.  
         [0028]     For the case wherein the exceeding of a limiting value of a braking torque of a drive motor is evaluated, the limiting value can be defined in accordance with various methods. One possibility is to predefine a maximum braking moment by a machine control system. For this purpose, entries can be made by an operator or automatically through interfaces. For example, data which relate to the material on the surface of the rollers can be processed. Furthermore, the characteristic number of the employed roller type can be entered. It is also possible to determine roller properties by detectors which evaluate a physical property of the roller surface or read the data from identifiers connected to the rollers.  
         [0029]     Monitoring the torque of one of the rollers can be made dependent upon the condition of the printing press. For example, the time period during which a limiting moment is exceeded can be evaluated. Furthermore, the torque can be monitored as a function of the printing unit temperature or of the system or mains voltage.  
         [0030]     The drive for at least one of the rollers can be set in various ways depending upon the torque. If an electric motor is used, the current, the voltage, the frequency or pulse characteristic variables can be changed. In this regard, the drive relationships can be set by reducing the friction between rollers by changing the coefficients of friction by adding ink, dampening solution or cleaning agent or by reducing the contact pressure between the rollers or by reducing the absolute speed of the two rollers.  
         [0031]     In accordance with the method of the invention, the cleaning time can be reduced by increasing, during cleaning, the speed of the machine and therefore the speed of the rollers to be cleaned, until a predefined level of friction is established between two rollers. When the predefined level of friction has been reached, the cleaning operation is completed.  
         [0032]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0033]     Although the invention is illustrated and described herein as embodied in a method for driving rollers of a printing unit of a printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0034]     The method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific modes of operation thereof when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]      FIG. 1  is a diagrammatic, side-elevational view of a printing unit of a wet offset printing press; and  
         [0036]      FIG. 2  is a schematic and block diagram relating to the monitoring and driving of rollers and cylinders of the printing unit according to  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a diagrammatic, side-elevational view of a printing unit  1  of a wet offset printing press. The printing unit  1  is made up of a printing form cylinder  2 , a transfer cylinder  3 , an impression cylinder, ink applicator rollers  4  to  7  and a dampening solution applicator roller  8 . The ink applicator rollers  4  to  7  and the dampening solution applicator roller  8  can be thrown onto a printing form  9  which is clamped on the printing form cylinder  2 . The ink applicator rollers  4  and  5 , on one hand, and  6  and  7 , on the other hand, are in rolling contact with respective ink transfer rollers  10  and  11 . The ink applicator roller  6  is in rolling contact with a further ink transfer roller  12 . An ink transfer roller  13  bridges the ink transfer rollers  10  and  12 . Furthermore, the printing unit  1  has an ink duct or fountain and an ink duct or fountain roller, both non-illustrated, as well as an ink ductor roller  14 , which is reciprocatingly movable between the ink duct or fountain roller and an ink transfer roller  15 . The ink transfer roller  15  is followed in rolling contact by further ink transfer rollers  16  to  19 , an ink distributor roller  20  being thrown onto the ink transfer roller  17 , and the ink transfer roller  19  making contact with the ink transfer roller  11 .  
         [0038]     A dampening unit  21  is provided which includes a dampening solution dip roller  22  projecting into a dampening solution container  23  which is filled with dampening solution  24  during printing. A dampening solution metering roller  25  and a dampening solution transfer roller  26  are thrown onto the dampening solution dip roller  22 . Furthermore, the dampening unit  21  includes respective dampening solution transfer rollers  27  in rolling contact with the dampening solution transfer roller  26  and the dampening solution applicator roller  8 . A bridging roller  29  connects the dampening solution applicator roller  8  and the ink applicator roller  7 . In order to clean the rollers and cylinders of the printing unit  1 , spraying devices  30  and  31 , for water  32  and a cleaning agent  33 , and a doctor blade device  34  having a doctor blade  35 , are provided. Nozzles of the spraying devices  30  and  31  are directed towards the surface of the ink transfer roller  17 . The doctor blade  35  is to be set against the ink transfer roller  10 .  
         [0039]     Two motors  36  and  37  are provided for driving the rollers and cylinders of the printing unit  1 . The motor  36  is the main drive motor of the wet offset printing press and feeds a torque into a drive gear train, to which the printing form cylinder  2 , the transfer cylinder  3 , the ink transfer rollers  10 ,  11 ,  16  and  18  and the dampening solution transfer roller  27  are connected. A drive connection between the rollers and cylinders and the respective motors  36  and  37  is symbolically illustrated by thin double lines  38 . The motor  37  represents an auxiliary drive having a drive connection to the dampening solution dip roller  22 . The ink applicator rollers  4  to  7 , the dampening solution applicator roller  8 , the ink transfer rollers  12 ,  13 ,  15 ,  17  and  19 , the ink distributor roller  20 , the dampening solution transfer rollers  26  and  27 , the dampening solution metering roller  25  and the bridging roller  29  are respectively driven by friction from the respectively adjacent actively driven rollers and the printing form cylinder  2 .  
         [0040]     The motors  36  and  37  are connected to a control and regulating device  39 . Rotational movement of the printing form cylinder  2  and of the dampening solution dip roller  22  is registered by rotary encoders  40  and  41 , which are connected to the control and regulating device  39 . A current sensor  42  having an output signal proportional to the torque or drive moment present on the dampening solution dip roller  22  is disposed in a feed line between the control and regulating device  39  and the motor  37 . An output from the current sensor  42  is connected to the control and regulating device  39 .  
         [0041]     Both during printing and during cleaning of the rollers and cylinders of the printing unit  1 , the motors  36  and  37  are driven in such a manner that slippage is produced between the dampening solution dip roller  22  and the adjacent dampening solution transfer roller  26 . During printing, the slippage is, for example, 75%, whereas during cleaning, the slippage is set to about 30%. Since the dampening solution transfer roller  26  is located between the dampening solution transfer roller  27  rotating at high speed and the dampening solution dip roller  22  rotating at lower speed, the dampening solution transfer roller  26  has an average rotational speed dependent upon the pressure with respect to the dampening solution transfer roller  27  and the dampening solution dip roller  22 .  
         [0042]     The control and monitoring of the motors  36  and  37  is illustrated in greater detail in  FIG. 2 . Within the control and regulating device  39 , in addition to a machine control system  43 , there is provided a drive control system  44  and a power section  45  for the motor  37 . The power section  45  includes an output stage  46  which supplies a current I, so that the motor  37  brakes the dampening solution dip roller  22 . An actual value I act  of the current measured by the current sensor  42  is a measure of the braking moment applied to the dampening solution dip roller  22 . The actual value I act  of the current is supplied to a comparator  47 , where it is compared with a desired or nominal value I des  formed by the drive control system  44 . A differential value between the actual and the desired values of the current is outputted to a controller  48  having a P characteristic. An actuating variable for the output stage  46 , which is generated in the controller  48 , causes the desired-actual difference in the current to be reduced or eliminated. Assurance is thereby provided that a defined slippage always occurs between the dampening solution dip roller  22  and the dampening solution transfer roller  26 .  
         [0043]     The desired value I des  is predefined based upon various parameters, events and operating modes. For this purpose, a desired value generator  49  is provided in the drive control system  44 . The desired value generator  49  has logic elements and/or computational aids for obtaining the desired current value I des , which are connected bidirectionally to the machine control system  43 . The machine control system  43  predefines whether the desired current value I des  is to be generated for the printing operation or the cleaning operation. The way in which the desired value for the cleaning operation is obtained is discussed below in greater detail.  
         [0044]     Desired or nominal rotational speeds for the motors  36  and  37  are predefined by the machine control system  43  for cleaning the rollers and cylinders of the printing unit  1 . A desired or nominal rotational speed value n des  for the motor  37  is compared with an actual rotational speed value n act  in a comparator  50 . The actual rotational speed value n act  is measured with a rotary encoder  41 . The nominal or desired-actual deviation of the rotational speeds n des  and n act  is supplied to a controller  51  having a PI characteristic. An output signal from the controller  51  forms an input variable for determining the desired or nominal value I des  for the current in the desired or nominal value generator  49 . A further input variable for determining the desired or nominal value I des  is a limiting value for a torque, which is predefined by the machine control system  43 . Since the braking moment on the dampening solution dip roller  22  depends directly upon the feed current I for the motor  37 , a limiting value for the desired or nominal value I des  is derivable from the limiting value for the torque. If the limiting value for the desired or nominal current I des  is exceeded, a feedback signal is then generated and processed in the machine control system  43 . With the aid of an actuator  52 , the machine control system  43  then controls further operations, such as a change in the speed of the motor  36 , the actuation of the spraying devices  30  and  31  or the adjustment of the pressure between the dampening solution transfer roller  26  and the dampening solution dip roller  22  and/or the dampening solution transfer roller  27 .  
         [0045]     Checking the deaeration of the spray pipes of the spraying devices  30  and  31  is afforded by the invention of the instant application. As long as there is only ink and dampening solution  24 , respectively, between the rollers thrown on in the printing unit  1 , a predetermined moment is required in order to maintain a predefined slippage at the dampening solution dip roller  22 . As long as there is air in the feed lines of the spray pipes, the moment will not change. The instant that cleaning agent  33  and water  32 , respectively, come onto the rollers, the moment will decrease. This change in the moment can be interrogated in order to generate a signal to the effect that deaeration has taken place.  
         [0046]     This application claims the priority, under 35 U.S.C. § 119, of German Patent Application 10 2004 031 946.4, filed Jun. 30, 2004; the entire disclosure of the prior application is herewith incorporated by reference.