Abstract:
A web printing press is provided. The web printing press includes at least one printing unit printing images on a web, at least one press component in direct contact with the web, a cutting device for cutting the web into sheets and a controller transmitting a virtual master signal to the at least one printing unit and at least one press component. A sensor senses the at least one press component or directly senses the web downstream of the at least one print unit and generates a sensor signal. A processor receives the sensor signal and the virtual master signal, the processor transmits a modified virtual master signal to the cutting device as a function of the received sensor signal. Methods are also provided.

Description:
[0001]    This claims the benefit of U.S. Provisional Application No. 61/368,144 filed Jul. 27, 2010, and hereby incorporated by reference herein. 
         [0002]    The present invention relates to printing presses, and more particularly to printing presses which utilize a virtual master to provide proper commands to various press components. 
     
    
     BACKGROUND 
       [0003]    U.S. Pat. No. 5,894,802 describes a method and apparatus for establishing an isolated position reference in a printing operation. To compensate for discrepancies that can arise over time between isolated position reference signals generated by different regulators, and to avoid problems in the printing process that would result from such discrepancies, the isolated position reference signals generated within the various regulators can be periodically corrected or standardized. In accordance with one of the exemplary embodiments, the isolated position reference signals are corrected or standardized at a time when the print unit chosen as the standard is not being influenced by transient disturbances. This configuration can, for example, be applied to an existing printing press that, due to original design limitations, cannot transmit the same isolated position reference signal to all of its drive units. 
       SUMMARY OF THE INVENTION 
       [0004]    One deficiency of this concept is that the system does not know or react to variations in roll motions. Any disturbances, such as a mechanical transmission error, will cause variations in the roll motions. These variations in roll motion cause the web to strain which shifts the print alignment relative to the cut. 
         [0005]    The present invention provides a web printing press that includes at least one printing unit printing images on a web, at least one press component in direct contact with the web and a cutting device for cutting the web into sheets. A controller transmits a virtual master signal to the at least one printing unit and at least one press component. A sensor senses the at least one press component or directly senses the web downstream of the at least one print unit and generates a sensor signal. A processor receives the sensor signal and the virtual master signal. The processor transmits a modified virtual master signal to the cutting device as a function of the received sensor signal. 
         [0006]    The present invention also provides a method for printing a web. The method includes the steps of printing a web using a printing unit receiving a virtual master signal, sensing a characteristic of a press component in direct contact with the web or directly sensing a characteristic of the web downstream of the printing unit and modifying the virtual master signal for a further press component downstream of the print unit and the press component as a function of the sensed characteristic. 
         [0007]    The present invention further provides a method for printing a web. The method includes the steps of printing a web using a printing unit receiving a virtual master signal, acting on the printed web with at least one press component receiving the virtual master signal, determining a deviation between the virtual master signal and an actual characteristic of the at least one press component and modifying the virtual master signal for a further press component downstream of the at least one press component as a function of the deviation. 
         [0008]    Preferred embodiments of the present invention may include one or more of the following features. The virtual master signal may include velocity, position and acceleration information. The modified virtual master signal may correct the print to cut alignment of the image printed on the web. The sensor may sense an actual velocity of the at least one press component or an actual velocity of the web downstream of the at least one press component. The processor may compare the actual velocity of the at least one press component or the actual velocity of the web downstream of the at least one press component with the virtual master signal and may provide the modified virtual master signal to compensate for any undesired variations. The web printing may include at least one web compensator for guiding the web to the cutting device, the web compensator may also receive the modified virtual master signal to correct any change in the print to cut alignment. The at least one press component may be driven by a dedicated motor and the cutting device may be driven by a dedicated motor. The at least one press component may be, for example, a chill unit or a slitter. The sensor may be an encoder on the at least one press component. 
         [0009]    Preferred embodiments of the present invention may also include one or more of the following features. Modifying the virtual master signal may include generating a modified virtual master signal and sending the modified virtual master signal to the further press component. Sensing a characteristic may include using an encoder on the press component. The further press component may be a cutting device cutting the web or a web compensator guiding the web. Determining a deviation may include sensing an actual velocity of the at least one press component. The method of printing may include the step of observing a characteristic of the printed web downstream of the at least one press component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows schematically a first exemplary embodiment of a printing press and virtual master control system of the present invention; and 
           [0011]      FIG. 2  shows schematically a second exemplary embodiment of a printing press and virtual master control system of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Printing presses may include a plurality of individually driven press components each having a dedicated motor. These individually driven press components may be, for example, print units, blanket cylinders, plate cylinders, chill units, slitters, cut cylinders and web or ribbon compensators. A printing press may employ a virtual master system to control the individually driven components. The virtual master system sends an identical, virtual master signal to each dedicated drive of the individually driven press components in order to maintain a uniform drive throughout the printing press during the printing process. The virtual master signal typically includes a velocity component and a position setpoint component. 
         [0013]    The virtual master signal does not compensate for real-time press activity. As a result, no drive has information about how the other drives are operating. So, the virtual master signal is not able to compensate for or react to variations, for example, roll motions, that may occur in the printing press components. Any disturbances, such as a mechanical transmission error, may cause variations in the roll motion of press components and affect the velocity of the press components, the velocity of the web and/or print-to-cut alignment. 
         [0014]    The variations in roll motion may cause strain in the web which shifts the print-to-cut alignment. Thus, the printed image is shifted with respect to the cut which may lead to waste or undesirable products. In accordance with the present invention, a modified virtual master signal is employed that compensates for variations in the web or press components and any resulting changes in print to cut register and alignment. A virtual master signal is sent to the cut cylinder and may be modified as desired to compensate for undesired roll motions or press/web variations. Thus, understanding system, web and register dynamics allows predictions of print relative to cut for various roll motions and other disturbances. 
         [0015]      FIG. 1  shows an embodiment of a virtual master control system in accordance with the present invention. A printing press  100  includes a plurality of individually driven press components. Printing units  20 ,  22 ,  24 ,  26  each print an image on a web  10 . Each print unit  20 ,  22 ,  24 ,  26  may print a different color, for example, cyan, magenta, yellow and black. Each print unit may  20 ,  22 ,  24 ,  26  be a perfecting offset print unit and include two blanket cylinders and two plate cylinders. Each print unit may include a motor or drive,  21 ,  23 ,  25 ,  27 , respectively. Alternatively, only one print unit may be driven and the remaining print units may be geared to the driven print unit. Each print unit drive  21 ,  23 ,  25 ,  27  is connected to a print unit controller  60 ,  62 ,  64 ,  66 . The printing press may preferably be a multicolor offset lithographic printing press; with for example four print units which receive the same virtual master signal. 
         [0016]    Other individually driven press components include a chiller  30  for chilling web  10  after web  10  has been printed on by print units  20 ,  22 ,  24 ,  26  and a slitter  40  for slitting web  10  into a plurality of ribbons. A cutting unit  50  may be provided to cuts web  10  or ribbons into sheets  12 . Chill unit  30  may include two chill rolls  32  and an encoder  34 . Chill rolls  32  may be in direct contact with web  10 . Chill rolls  32  are driven by a motor  36  which is connected to a controller  68 . Encoder  34  measures the actual velocity of chill roll  32 . 
         [0017]    Slitter  40  may slit web  10  into a plurality of ribbons. Slitter  40  includes a slitting cylinder pair  42 ,  44  having at least one knife  41  or blade for slitting web  10  in the direction of web travel. Slitting cylinder pair  42 ,  44  includes an encoder  46  for measuring the actual velocity of slitting cylinder pair  42 ,  44 . Slitter  40  also includes a motor  48  that drives cylinder pair  42 ,  44 . Motor  48  is connected to a controller  70 . Slitting cylinder pair  42 ,  44  may be in direct contact with web  10  as slitter blade  46  slits web  10 . 
         [0018]    Cutting unit  50  includes a cutting cylinder pair  52 ,  54  having at least one knife  51  or blade for cutting the web  10  across the direction of travel into sheets  12 . Cutting unit  50  is individually driven by a respective motor  56  which is connected to a controller  72 . 
         [0019]    Each motor  21 ,  23 ,  25 ,  27 ,  36 ,  48  is connected to a respective controller  60 ,  62 ,  64 ,  66 ,  68 ,  70  in printing press  100 . Alternatively, each motor may be connected to one controller or any desired number of controllers. Each controller  60 ,  62 ,  64 ,  66 ,  68 ,  70  is connected to a virtual master processing device  80 . Virtual master processing device  80  sends a signal  81  to each controller  60 ,  62 ,  64 ,  66 ,  68 ,  70  thereby instructing each controller  60 ,  62 ,  64 ,  66 ,  68 ,  70  to operate corresponding motor  21 ,  23 ,  25 ,  27 ,  36 ,  48 . Signal  81  includes position, velocity and acceleration commands for motors  21 ,  23 ,  25 ,  27 ,  36 ,  48 . 
         [0020]    Since chill rolls  32  and slitting pair  42 ,  44  contact web  10  directly during printing operation, any deviations in the actual velocity relative to the desired velocity of chill rolls  32  and slitting pair  42 ,  44  will cause web  10  to strain and affect the print-to-cut register of cutting cylinder pair  52 ,  54 . Thus, in accordance with the present invention, encoders  34 ,  46  are used to determine the actual velocity of chill rolls  32  and slitting pair  42 ,  44 . Actual velocity  37  of chill rolls  32  and actual velocity  49  of slitting cylinder pair  52 ,  54  are sent to web and register processor  84 . Web and register processor  84  compares the virtual master signal  81  with actual velocities  37 ,  49  and estimates how much a printed image has shifted on the web  10  relative to the anticipated cut. Web and register processor  84  then transmits a modified virtual master signal  86  to controller  72  of cutting device  50  to compensate for any roll motion deviations or variation in chill unit  30  or slitter  40 . Thus, modified virtual master signal  86  controls motor  56 . Modified virtual master signal  86  transmitted to cutting device  50  may be different then virtual master signal  81  transmitted by processor  80  since modified signal  86  compensates for variations and changes in web characteristics or press components, specifically variations and changes that may affect print-to-cut register. 
         [0021]    For example, if a mechanical disturbance causes chill roll motor  36  to move relative to the chill roll  32  itself, actual velocity  37  measured at the chill roll  32  or web  10  at the chill unit  30 , will differ from virtual master velocity included in virtual master signal  81 . Web and register processor  84  measures this difference, and transmits a modified virtual master signal  86  to cutting device  50  to correct for the variation. Thus, controller  72  controls the speed of motor  56  based on the information provided in modified virtual master signal  86 . 
         [0022]    Being able to observe a characteristic of web  10  and/or press components  30 ,  40  provides real time information for printing press  100 . With this information, processor  84  can calculate or determine the deviation between virtual master signal  81  and the observed qualities of web  10  or press components  30 ,  40 , for example, actual velocities  37 ,  49 . By updating the virtual master signal  81  with a modified virtual master signal  86  errors in downstream processing, for example, cutting the web into sheets, may be reduced. The observed characteristics of the web and/or press components may be directly sensed from the web or press components themselves or determined empirically or any combination thereof. 
         [0023]    In another preferred alternative, sensors on web may be used to determine the web velocity or strain on the web. Sensors may be located downstream of each individually driven component to detect the fluctuations in web characteristics. 
         [0024]    In a further preferred embodiment, virtual master processor  80  may send virtual master signal  81  to controller  72  of cutting device  50 . Web and register processor  84  may then send a modified virtual master signal  86  to controller  72 . Based on the differences between signals  81 ,  86 , controller  72  will advance or retard motor  56  as needed. Alternatively, if virtual master signal  81  is sent to controller  72 , modified virtual master signal  86  many only include information for modifying the original virtual master signal  81  as desired instead of tranmitting a new, complete modified virtual master signal  86 . 
         [0025]    A modified virtual master signal may also be employed in duplex web presses. In this case the web compensators for each press are modified along with the cutting device. Observed characteristics, for example, roll motion information, from each press are used to estimate the shift of the print relative to the cut. Since the effect of these observed characteristics can be estimated, modified signals can be sent to the web compensators and cutting device which minimizes the shift of the print relative to the cut caused by variations or disturbances during printing, for example, roll motion in press components. 
         [0026]      FIG. 2  shows an embodiment of the virtual master control system for a duplex press  200  in accordance with another preferred embodiment of the present invention. Duplex press  200  includes two presses,  100 ,  100 ′ which include components similar to those in printing press  100  shown in  FIG. 1 . The same components are identified by the same reference numerals and will not be described in detail again. Printing press  200  includes printing units  20 ,  20 ′ driven by motors  21 ,  21 ′ which are connected to controllers  60 ,  60 ′, respectively. More than one printing unit may be provided for each web  10 ,  10 ′. Chill units  30 ,  30 ′ are individually driven by motors  36 ,  36 ′ which are connected to controllers  68 ,  68 ′. Encoders  34 ,  34 ′ on one of chill rolls  32 ,  32 ′ records the actual velocity  37 ,  37 ′ of chill rolls  32 ,  32 ′. Slitters  40 ,  40 ′ are individually driven by motors  48 ,  48 ′ which are connected to controllers  70 ,  70 ′. Slitting pairs  42 ,  44 ,  42 ′,  44 ′ include encoders  48 ,  48 ′ for measuring the actual velocity  49 ,  49 ′ of slitting pairs  42 ,  44 ,  42 ′,  44 ′. Web compensators  90 ,  90 ′ are provided for guiding webs  10 ,  10 ′ to cutting device  50 . Chill units  30 ,  30 ′, slitters  40 ,  40 ′ and web compensators  90 ,  90 ′ directly contact webs  10 ,  10 ′, thus any variation in roll motion of these components may change the velocity of webs  10 ,  10 ′ and affect print to cut register. 
         [0027]    Each controller  60 ,  68 ,  70 ,  60 ′,  68 ′,  70 ′ is connected to a virtual master processing device  80 . Virtual master processing device  80  sends a signal  81  to each controller  60 ,  68 ,  70 ,  60 ′,  68 ′,  70 ′ to operate corresponding motor  21 ,  36 ,  48 ,  21 ′,  36 ′,  48 ′. Signal  81  includes position, velocity and acceleration commands for each press  100 ,  100 ′. 
         [0028]    Web and register processor  84  estimates the amount the print shift relative to the cut for each web  10 ,  10 ′ based on roll motion variations. Virtual master processing device  80  sends a virtual master signal  81  to a web and register processor  84 . Actual roll velocities  37 ,  49 ,  37 ′,  49 ′ are also inputs to web and register processor  84 . Web and register processor  84  calculates the estimated amount the print shifted relative to the cut and uses this estimate to transmit modified virtual master signals  88 ,  88 ′,  86 . Web compensators  90 ,  90 ′ receive modified virtual master signals  88 ,  88 ′, respectively. Processor  84  transmits modified virtual master signal  86  to cutting device  50 . Alternately, ribbon compensators can be used instead of or in conjunction with the web compensators  90 ,  90 ′. In an alternative preferred embodiment, web compensators  90 ,  90 ′ and/or cutting device  50  may each be connected to controllers that receive the modified virtual master signals  88 ,  88 ′,  50 , respectively. 
         [0029]    In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.