Abstract:
A tension control device for a printing press having an adjustment roller, with a web of the press passing from a supply roll of the web to the adjustment roller. Means are provided for measuring the tension on opposed sides of the web passing downstream from the adjustment roller, and means are provided responsive to the measuring means for automatically approximately equalizing the tension of the web by adjustment of the adjustment roller on one end only of the adjustment roller.

Description:
RELATED APPLICATION  
       [0001]    This is a continuation-in-part of U.S. application Ser. No. 09/294,921, filed Apr. 19, 1999, which is a continuation of U.S. application Ser. No. 08/908,008, filed Aug. 11, 1997, now U.S. Pat. No. 5,894,797, which is a continuation of U.S. application Ser. No. 08/734,552, filed Oct. 17, 1996, now abandoned, which is a continuation of U.S. application Ser. No. 08/521,157, filed Aug. 30, 1995, now abandoned. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to tension control devices for a printing press.  
         BACKGROUND OF THE INVENTION  
         [0003]    Before the present invention, multi-color printing units have been used in a printing press to print colored images on a paper web. The webs used in the press unwind the web from a supply roll, and may be centered on the rollers of the press or may be positioned off-center. Due to the relatively fast speed of the press, the rolls have been completely unwound in a relatively short period of time, such as 15 minutes.  
           [0004]    In accordance with prior practice, a new roll of the web is pasted onto the web of the previous roll when it is almost depleted. However, the rolls each have different characteristics, such as different manufacture and different winding tensions. As a result, the tension on opposed sides of the new web becomes significantly different, causing loss of registration in the press and flapping of the web, which may cause a web break.  
           [0005]    Adjustments must be made to the press in the event of loss of registration, and due to the relative frequency of web pasting. Such adjustments result in loss of press time, wasted product, and inconvenience to the operator of the press.  
         SUMMARY OF THE INVENTION  
         [0006]    In accordance with certain aspects of the present invention, a tension control device is provided for a printing press. The device includes an adjustment roller, with a web of the press passing from a supply roll of the web to the adjustment roller. Means are provided for measuring the tension on opposed sides of the web passing downstream from the adjustment roller. Means responsive to the measuring means are provided for automatically approximately equalizing the tension of the web by adjustment of the adjustment roller on one end only of the adjustment roller.  
           [0007]    In accordance with additional aspects of the present invention, a tension control device is provided for a printing press. The device includes an adjustment roller and a tension roller positioned downstream of the adjustment roller, with a web of the press passing from a supply roll to the adjustment roller and tension roller, wherein the web is positioned off-center with respect to the adjustment roller and tension roller. Means are provided for measuring the tension on opposed ends of the tension roller, wherein a tension differential is detected at the opposed ends of the tension roller when the tension at opposed sides of the web are substantially equal. Means responsive to the measuring means are provided for automatically approximately equalizing the tension at opposed sides of the web by adjusting the adjustment roller on one end only of the adjustment roller to maintain the tension differential.  
           [0008]    In accordance with further aspects of the present invention, a tension control device is provided for a printing press having a web. The device includes an adjustment roller and a tension roller located downstream of the adjustment roller, wherein the web passes over the adjustment roller and tension roller. A pair of transducers are provided for measuring tension at opposed ends of the tension roller, and means are provided for adjusting one end only of the adjustment roller. A controller controls the adjusting means in response to the transducers to approximately equalize tension on opposed sides of the web.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a diagrammatic view of a printing press for use with a tension control device of the present invention;  
         [0010]    [0010]FIG. 2 is a side elevation view of the tension control device;  
         [0011]    [0011]FIG. 3 is a diagrammatic view of a tension roller for the device of FIG. 2; and  
         [0012]    [0012]FIG. 4 is a block diagram of a control system of the tension control device of FIG. 2. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    Referring now to FIG. 1, there is shown a printing press generally designated  10  for printing an image on a paper web  14 . The press  10  has a plurality of printing units  28 ,  30 ,  32 , and  34  for printing different colors of ink on the web  10 . As shown, the printing unit  28  may print an ink having a color Cyan C, the printing unit  30  may print an ink having a color Magenta M, the printing unit  32  may print an ink having the color Yellow Y, and the printing unit  34  may print an ink having a color Black K in a four-color press  10 .  
         [0014]    The printing units  28 ,  30 ,  32 , and  34  each have a plurality of print rolls or cylinders  36  associated with a blanket cylinder or roll  40 . During printing by the press  10 , an image of the ink is transferred from the print rolls  36  to the associated blanket rolls  40  to print the image on one surface of the web  14 . In addition, the press  10  may have a plurality of printing units having a plurality of print rolls  38  associated with a plurality of blanket rolls or cylinders  42  on an opposed surface of the web  14  in order to transfer the ink image from the print rolls  38  to the blanket rolls  42  for printing an image on the other surface of the web  14 . The following description of the print rolls is equally applicable to either the print rolls  36  or the print rolls  38  on the opposed surfaces of the web  14 .  
         [0015]    With reference to FIG. 2, the press  10  has a device  50  for controlling tension of the web  14  of the press  10 . As shown, the web  14  passes from a supply roll around an adjustment roller  52  to a tension roller  54 . The web  14  passes from the tension roller  54  around a dancer roller  56  to an idler roller  58  and then to the printing units of the press  10 .  
         [0016]    With reference to FIG. 4, the press  10  has a control system  62  having a computer  60  or Central Processing Unit (CPU) having a Random Access Memory (RAM) and Read Only Memory (ROM). As will be seen below, the control system  62  controls operation of the device  50 , as shown in FIG. 2.  
         [0017]    As shown in FIGS. 2 and 3, the tension roller  54  has transducers  64  and  66  on opposed ends of the tension roller  54 . The transducers  64  and  66  are of known type, and measure the tension caused by the web  14  on opposed ends of the tension roller  54 .  
         [0018]    With reference to FIG. 2, the adjustment roller  52  has a bearing cup  68  on one end only of the adjustment roller  52 , along with a bearing housing  70  for the cup  68 . The bearing housing  70  has a bore  72  having inwardly directed helical teeth  74 . The device  50  has an elongated shaft  76  having outwardly directed helical teeth  78  which mesh with the teeth  74 . The device  50  has an elongated shaft  80  having the teeth  78  in the region of the bearing housing  70 , while the housing  70  has the teeth  74  which mesh with the teeth  78  of the shaft  80 . Thus, rotation of the shaft  80  causes a displacement of the bearing cup  68 . In this manner, the tension of the web  14  on the one end of the adjustment roller  52  may be adjusted, which takes place automatically since the shaft  80  is rotated by a two-speed motor  82  attached to the shaft  80 . The device  50  also has an elongated hand wheel  84  attached to an opposed end of the shaft  80  relative to the motor  82  in order to make manual adjustments to the shaft  80 , with the automatic system off, if desired.  
         [0019]    The device  50  may be operated to sense a difference in tension on the transducers  64  and  66  and to equalize the tensions on opposed sides of the web  14 . When the web  14  is substantially centered on the tension roller  54 , it is desired to obtain an identical tension on the opposed ends of the tension roller  54  in order to compensate for the paste of the web  14  from a depleted roll of web  14  to a new roll of the web  14 . The condition of pasting a new roll of web  14  usually causes the device  50  to determine a different tension on the transducers  64  and  66 .  
         [0020]    In the event of the differing tension of the transducers  64  and  66 , the device  50  actuates the motor  82  to rotate the shaft  80  and cause displacement of the bearing cup  68  and the one end of the adjustment roller  52 . The motor  82  operates on the shaft  80  in a direction which will minimize the difference in tension on the transducers  64  and  66  of the tension roller  54 . In this manner, the press  10  compensates for the web paste and minimizes the occurrence of the loss of registration and flapping of the web  14  due to the web pastes.  
         [0021]    In certain situations where the web  14  is off-center, such as when running a partial web, the device  50  may also be operated to maintain substantially equal tensions at opposed sides of the web  14  by detecting tension on the transducers  64  and  66  and maintaining a pre-set tension differential between the opposed ends of the tension roller  54 . When a partial web is run, the web  14  is often positioned to one end of the rollers, as shown in phantom in FIG. 3. Consequently, the longitudinal centerline  15  of the web  14  is spaced from a center  55  of the tension roller  54 . For example, the web centerline  15  may be closer to the right end of the tension roller  54 , as shown in FIG. 3, and therefore closer to the transducer  66 . As a result, when the tension at opposed sides of the web  14  is substantially equal, the tension measured at transducer  66  is greater than the tension measured at transducer  64 . It is desirable, however, to maintain the tension differential at the ends of the tension roller  54  so that the web tension is substantially equalized.  
         [0022]    The desired tension differential when running an off-center web is primarily a function of web width and web position on the tension roller  54 . Assuming, for example, that the web  14  is a partial web having a width approximately equal to one-half the width of the tension roller  54 , and that the partial web is positioned so that its right side is substantially even with the right of the tension roller  54 , as shown in FIG. 3. In this example, the longitudinal centerline  15  of the web  14  passes over the tension roller  54  at a point midway between the center  55  of the tension roller and the right end of the tension roller. As a result, the distance from the centerline of the web  14  to the right end is approximately one-fourth of the total width of the tension roller  54 , while the distance from the web centerline  15  to the left end of the tension roller  54  is three-fourths of the tension roller width. It is expected that the measured tensions on the ends of the tension roller  54  should be roughly inversely proportional to the distances from the web centerline  15  to the ends of the tension roller, or  3 : 1  in the stated example. Accordingly, the tension measured at the right transducer  66  should be approximately three times the tension measured at the left transducer  64 .  
         [0023]    The tension differential approximation may be affected by several additional factors, such as the geometry of the rollers, whether the web  14  is wound evenly across the roller, and other considerations, and therefore the relationship between tension and web position is not necessarily linear.  
         [0024]    In any event, once the desired tension differential is determined, the CPU  60  may be programmed to adjust one end of the tension roller  54  so that the tension differential at the transducers  64  and  66  is maintained. If the tensions measured at the transducers  64  and  66  produce a differential other than the desired value, the device  50  actuates the motor  82  to adjust the shaft  80  as noted above, thereby to obtain the desired tension differential.  
         [0025]    As shown in FIG. 2, the device  50  also has a limit switch  86  which signals the computer  60  in the event that a predetermined limit on adjustment of the adjustment roller  52  takes place, in which case the motor  82  is deactivated.  
         [0026]    The transducers  64  and  66  can measure when the web  14  is initially pasted due to relatively high fluctuation of the tension on opposed ends of the tension roller  54 . In this case, the motor  82  runs at a first fast speed in order to make coarse corrections to the one end of the adjustment roller  52  as controlled by the CPU. Once the coarse corrections have been made by the motor  82 , the CPU causes the motor  82  to move at a second slow rate in order to make fine adjustments to the one end of the adjustment roller  52 . In this manner, the one end of the adjustment roller may be adjusted in a rapid and accurate manner.  
         [0027]    Fine adjustments are made as the expiring roll decreases to adjust for small variations in tension.  
         [0028]    Although certain exemplary apparatus constructed in accordance with the teachings of the invention have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all embodiments of the teachings of the invention fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.