Patent Publication Number: US-2005115428-A1

Title: Strip printing unit for an automatic machine

Description:
The present invention relates to a strip printing unit for an automatic machine.  
      The present invention may be used to advantage in an automatic cigarette manufacturing machine, to which the following description refers purely by way of example.  
     BACKGROUND OF THE INVENTION  
      On an automatic cigarette manufacturing machine, a strip of paper is unwound off a reel and fed to a tobacco bead forming beam where it is folded about the tobacco bead. The machine normally also comprises a printing unit located along the path of the paper strip and for printing symbols and/or writing on the strip.  
      Known printing units normally comprise a printing roller with printing areas on its lateral surface; a pressure roller which cooperates with the printing roller to press the paper strip against the lateral surface of the printing roller; and a number of inking rollers for depositing ink on the printing areas of the printing roller. In use, the paper strip is fed between the printing roller and the pressure roller, and is printed cyclically by the printing areas on the printing roller.  
      During operation of the automatic cigarette manufacturing machine, format changes are frequently necessary to change the type of cigarettes produced on the machine, and which normally also involve changing the printing areas on the lateral surface of the printing roller, or the printing roller as a whole. Once the change is made, the position of the printing roller with respect to the pressure roller must be adjusted accurately to obtain the best pressure of the pressure roller on the printing roller. With known printing units, adjusting the position of the printing roller with respect to the pressure roller is a particularly time-consuming job, in which the operator must stop the machine repeatedly to make a position change, and then start the machine up again to check the print quality. Printing roller to pressure roller position adjustments therefore call for skilled labour for a relatively prolonged period of time, during which, cigarette production is halted, thus reducing the average output of the machine.  
      DE 4413735 discloses a printing unit comprising a printing roller  4  (i.e. a roller designed for depositing ink on a strip  14 ) and a pressure roller  2 ; the position of the printing roller  4  is adjustable with respect to the pressure roller  2 . The unit disclosed by DE 4413735 has several drawbacks: inter alia, since the printing roller is moveable, the ink feeding devices of the unit are relatively complex, as they are designed to adapt their configuration to the different positions of the printing roller  4 .  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a strip printing unit for an automatic machine, designed to eliminate the aforementioned drawbacks, and which, in particular, is cheap and easy to produce.  
      According to the present invention, there is provided a printing unit for printing a strip on an automatic machine; the printing unit comprising a printing roller with printing areas on its lateral surface, and a pressure roller which cooperates with the printing roller to press the strip against the lateral surface of the printing roller; the printing unit being characterized by comprising a first actuator for adjusting the position of the pressure roller with respect to the printing roller; a non-contact sensor facing the printed surface of the strip, downstream from the printing roller, and for determining the intensity of the print on a printed surface of the strip; and a control unit for adjusting the position of the pressure roller with respect to the printing roller as a function of the print intensity determined by the non-contact sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:  
       FIG. 1  shows a schematic side view of a preferred embodiment of a strip printing unit in accordance with the present invention;  
       FIG. 2  shows a larger-scale view of part of the  FIG. 1  printing unit and illustrating a servo-assisted adjusting system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Number  1  in  FIG. 1  indicates as a whole a printing unit for printing a paper strip  2  on an automatic cigarette manufacturing machine (not shown). More specifically, paper strip  2  is unwound off a reel (not shown), is fed through printing unit  1 , and is then fed to a tobacco bead forming beam (not shown) where it is folded about the tobacco bead.  
      Printing unit  1  comprises a printing roller  3  fitted in a fixed position to a frame  4  of the automatic machine, and rotated continuously by an electric motor (not shown) about an axis  5  perpendicular to the  FIG. 1  plane. Printing roller  3  has three printing areas  6  equally spaced on the lateral surface of printing roller  3 , and which are pressed against strip  2  to print strip  2 . A pressure roller  7  cooperates with printing roller  3 , and is rotated continuously about an axis  8  parallel to axis  5  of printing roller  3  to press strip  2  against the lateral surface of printing roller  3 . More specifically, pressure roller  7  is fitted in rotary manner to a frame  9 , in turn fitted in rotary manner to frame  4  of the automatic machine to oscillate about an axis  10  parallel to axis  5  of printing roller  3 .  
      Printing unit  1  also comprises an inking assembly  11  for depositing ink on printing areas  6  of printing roller  3 . Inking assembly  11  comprises an inking roller  12  mounted to rotate continuously about an axis  13  parallel to axis  5  of printing roller  3 , and for depositing ink on printing areas  6  of printing roller  3 ; and an inking roller  14  mounted to rotate continuously about an axis  15  parallel to axis  5  of printing roller  3 , and for depositing ink on inking roller  12 . Inking rollers  12  and  14  are fitted in rotary manner to a frame  16 , in turn fitted in rotary manner to frame  4  of the automatic machine to oscillate about an axis  17  coaxial with axis  15  of inking roller  14 .  
      Inking assembly  11  also comprises an inking roller  18  mounted to rotate continuously about an axis  19  parallel to axis  5  of printing roller  3 , and for depositing ink on inking roller  14 ; an inking roller  20  mounted to rotate continuously about an axis  21  parallel to axis  5  of printing roller  3 , and for depositing ink on inking roller  18 ; a sprayer  22  for depositing ink on inking roller  20 ; and a coating roller  23  mounted to rotate continuously about an axis  24  parallel to axis  5  of printing roller  3 , and which cooperates with inking roller  20  to coat inking roller  20  with the ink sprayed by sprayer  22 . Inking rollers  18  and  20  are fitted in rotary manner to a frame  25 , in turn fitted in rotary manner to frame  4  of the automatic machine to oscillate about an axis  26  coaxial with axis  21  of inking roller  20 .  
      The fact that the axis  17  of oscillation of frame  16  is coaxial with axis  15  of inking roller  14  enables frame  16  to oscillate about axis  17  to adjust the position of inking roller  12  with respect to printing roller  3  without in any way affecting the connection between inking roller  14  and inking roller  18 . Similarly, the fact that the axis  26  of oscillation of frame  25  is coaxial with axis  21  of inking roller  20  enables frame  25  to oscillate about axis  26  to adjust the position of inking roller  18  with respect to inking roller  14  without in any way affecting the connection between inking roller  20  and coating roller  23 .  
      As shown in  FIG. 2 , an electric actuator  27  is provided to control oscillation of frame  9  about axis  10  to adjust the position of pressure roller  7  with respect to printing roller  3 . More specifically, frame  9  is connected mechanically to actuator  27  by a transmission (not shown in detail) which keeps frame  9  in a fixed position when actuator  27  is idle, and which comprises a screw integral with actuator  27 , and a nut screw connected to the screw and integral with frame  9 .  
      An electric actuator  28  is also provided to control oscillation of frame  16  about axis  17  to adjust the position of inking roller  12  with respect to printing roller  3 . More specifically, actuator  28  comprises an eccentric body  29  which engages a respective seat  30  formed in frame  16 , and is oscillated about an axis parallel to axis  5  of printing roller  3  to adjust the position of inking roller  12  with respect to printing roller  3 . To keep frame  16  in a fixed position when actuator  28  is idle, frame  16  is provided with elastic fastening members  31  which keep frame  16  pressed against frame  4  to oppose oscillation of frame  16  with a given force lower than the force generated by actuator  28 . Each fastening member  31  comprises a central threaded pin  32  which is inserted inside a respective seat  33  formed in frame  16 , is screwed at one end to frame  4 , and at the opposite end is screwed to a knob  34  which compresses a Belleville washer (not shown) against frame  4 . To keep frame  25  in a fixed position, frame  25  is provided with an elastic fastening member  35  ( FIG. 1 ) identical with fastening members  31  described above.  
      Printing unit  1  also comprises a television camera  36  located downstream from printing roller  3  and facing the printed surface of paper strip  2  to pick up a real-time image of the print on paper strip  2 . Camera  36  is connected to a control unit  37  which drives both actuators  27  and  28  to control both the angular position of frame  9 , and therefore of pressure roller  7  with respect to printing roller  3 , and the angular position of frame  16 , and therefore of inking roller  12  with respect to printing roller  3 .  
      In actual use, control unit  37 , by means of camera  36 , determines the intensity of the print on the printed surface of strip  2  and, accordingly, adjusts the position of pressure roller  7  with respect to printing roller  3 . For example, pressure roller  7  is moved closer to printing roller  3  if the intensity of the print is below a desired value, and is moved away from printing roller  3  if the intensity of the print is above the desired value. In use, control unit  37  also adjusts the position of inking roller  12  with respect to printing roller  3  by driving actuator  28 . For example, inking roller  12  is moved closer to printing roller  3  if the intensity of the print is below a desired value, and is moved away from printing roller  3  if the intensity of the print is above the desired value. In a different embodiment not shown, camera  36  is replaced with a different non-contact sensor for determining the intensity of the print on the printed surface of strip  2 .  
      In one possible embodiment, a position sensor  38  (in particular, an angular encoder) is connected to control unit  37 , and determines the angular position of frame  9  about axis  10 , and therefore the position of pressure roller  7  with respect to printing roller  3 . Using position sensor  38 , control unit  37  is able to set a predetermined position of printing roller  3  with respect to pressure roller  7 , depending on the characteristics of printing areas  6  on printing roller  3 . A position sensor  39  (in particular, an angular encoder) is also connected to control unit  37 , and determines the angular position of frame  16  about axis  17 , and therefore the position of inking roller  12  with respect to printing roller  3 . Using position sensor  39 , control unit  37  is able to set a predetermined position of inking roller  12  with respect to printing roller  3 , depending on the characteristics of printing areas  6  on printing roller  3 . Position sensors  38  and  39  are obviously also employed by control unit  37  to feedback-control actuators  27  and  28  for adjusting the angular position of frame  9 , and therefore of pressure roller  7  with respect to printing roller  3 , and the angular position of frame  16 , and therefore of inking roller  12  with respect to printing roller  3 .  
      In a further embodiment, a force sensor  40  is connected to control unit  37 , and determines the contact force between printing roller  3  and pressure roller  7 . In actual use, control unit  37  prevents a predetermined maximum value of the contact force between printing roller  3  and pressure roller  7  from being exceeded, so as to avoid subjecting printing areas  6  to excessive mechanical stress, and so avoid damaging paper strip  2 . A force sensor  41  is also connected to control unit  37 , and determines the contact force between inking roller  12  and printing roller  3 . In actual use, control unit  37  prevents a predetermined maximum value of the contact force between inking roller  12  and printing roller  3  from being exceeded, so as to avoid subjecting printing areas  6  to excessive mechanical stress.  
      Printing unit  1  as described above therefore provides for fully independently and automatically adjusting the position of pressure roller  7  and inking roller  12  with respect to printing roller  3 , to achieve optimum printing quality. When making a format change, once printing roller  3  or printing areas  6  on the lateral surface of printing roller  3  have been changed, printing unit  1  need simply be started up again, and, in the space of a few seconds, is capable of independently and automatically achieving optimum printing quality, thus greatly simplifying and speeding up format changes of printing unit  1 . Moreover, once the format change is completed, and before printing unit  1  is started up, the operator may inform control unit  37  of the type of printing roller  3  or printing areas  6  currently fitted to printing roller  3 , so that, before printing unit  1  is started up, control unit  37  can set the initial positions of pressure roller  7  and inking roller  12  with respect to printing roller  3  on the basis of predetermined values stored in a memory of the control unit and depending on the characteristics of printing roller  3  or printing areas  6  on printing roller  3 .  
      In a further embodiment not shown, oscillation of frame  25  about axis  26  may also be powered, like frame  16 , to enable control unit  37  to also adjust the position of inking roller  18  with respect to inking roller  14 .  
      Printing unit  1  as described above may obviously be used in any automatic machine other than an automatic cigarette manufacturing machine, such as an automatic cigarette packing machine, an automatic food packing machine, and, in general, any automatic machine involving printing strip material.