Abstract:
Method and arrangement for controlling the temperature of two cylinders forming a nip. The temperature of at least one point on each cylinder is sensed by sensors, forming a point of measuring, wherein the highest sensed temperature is used as set point and wherein the cylinders are heated in areas where the sensed temperature is below the set point.

Description:
TECHNICAL FIELD 
       [0001]    The present invention concerns a system and a method of controlling and balancing the temperature of two cooperating cylinders forming a nip. 
       PRIOR ART 
       [0002]    In many circumstances where two cylinders form a nip it is most important that the distance between the cylinders are kept within a certain range. Often it is also important that cooperating parts of the cylinders are kept in line with each other. 
         [0003]    For many types of cylinders such as scoring cylinders forming a nip it is important that they are properly aligned in relation to each other. In machines for forming containers from a web of a paper or laminate material, there are normally scoring cylinders at some stage. Scores are formed in the web, to assist in the folding of the packages. One of the scoring cylinders has projections that are to go into interacting grooves of the other cylinder. Not properly aligned scoring cylinders may lead to cuts in the web to be scored. When cylinders are heated they will expand. If scoring cylinders are unevenly heated they will expand unevenly which may lead to that cooperating parts of the cylinders does not align properly. Thus, the projection of one cylinder may hit the sides of the grooves of the other cylinder, which probably will cut the web. 
       SUMMARY OF THE INVENTION 
       [0004]    In view of the above one object of the present invention is to eliminate or at least reduce the risk of cutting of a web at a scoring unit due to uneven heating. 
         [0005]    One aspect of the present invention is to control the temperature of the two cylinders forming the nip. According to the invention the temperature of the cylinders including bearings and drive are measured continuously in a number of separate points. The algorithm for the temperature control is based on the highest registered temperature, which temperature will form the set point. The other parts of the cylinders, bearings and drive are then heated to the registered highest temperature, i.e. the set point. 
         [0006]    In another aspect of the present invention the temperature at different parts of the cylinders, bearings and drive are still registered. Heaters ate still provided for heating of the different parts of the cylinders. However, according to this aspect of the present invention the cylinders are placed displaceable at the ends in relation to each other. Either only one or both cylinders are displaceable. The cylinder or cylinders are displaced based on the sensed temperatures. 
         [0007]    By means of the present invention the temperature of the cylinders are evenly distributed. Without a control system such as according to the present invention there may be a relatively large difference between the highest and the lowest temperature of the cylinders of the nip. 
         [0008]    Even tough the present invention is normally described in connection with scoring cylinders at machines for forming containers, a person skilled in the art realises that the principles of the present invention may be used for other cylinders forming a nip. 
         [0009]    The control cycle of the present invention is developed for webs having a thickness of at least 150 μm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention will be described further below by way of examples and with reference to the enclosed Figs. In the Figs., 
           [0011]      FIG. 1  is a schematic side view of two scoring cylinders incorporating the present invention, 
           [0012]      FIG. 2  is a detailed view of a part of a nip of the scoring cylinders of  FIG. 1 , 
           [0013]      FIG. 3  is one example of a heater assembly that may be used with the present invention, and 
           [0014]      FIG. 4  is a schematic end view of one of the cylinders of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0015]    In  FIG. 1  two scoring cylinders  1 ,  2  are shown, as one example. Each end of the cylinders  1 ,  2  is received in a bearing housing  3 ,  4 ,  5 ,  6 . One of the bearing housings  6  includes a drive unit. 
         [0016]    One of the scoring cylinders  1  has projections  8  formed on the surface of the cylinder  1 . The projections  8  are to be received in grooves  7  of the other scoring cylinder  2 . If the cylinders  1 ,  2  are unevenly heated they will expand in various degrees. If the projection  8  of one scoring cylinder  1  due to such uneven heating gets too close to the groove  7  of the other cylinder  2 , the web to be scored may be cut in the contact between projection  8  and groove  7 . 
         [0017]    Heaters  23 - 28  are arranged along each cylinder  1 ,  2 . Normally at least three heaters  23 - 28  are arranged for each cylinder  1 ,  2 , one at each end and one in the middle. A person skilled in the art realises that the exact number of heaters are decided in each case depending on the dimensions of the cylinders, the demands on sensitivity etc. In  FIG. 3  one example of a heater is shown as a ramp  9  having a number of IR-carbon light heaters  10 . In this embodiment heaters may be placed also inside the bearing housings  3 - 6 , which heaters may be air heaters. In other embodiments there are no heaters in the bearing housings  3 - 6  as the drive unit and bearings normally generates much of the heat during use. The bearing housings  3 - 6  include oil that assists in distributing the generated heat inside the bearing housings  3 - 6 . 
         [0018]    A sensor  11  is associated with at least each heater  23 - 28  but further sensors may be arranged. The sensors  11  measure the temperature at specific points  12 - 21  on the cylinders or parts associated with the cylinders. The sensors  11  are normally IR-sensors, but any suitable type of sensor may be used. 
         [0019]    In use one IR-sensor  11  is directed against points of measuring  13 - 15 ,  17 - 19  on the cylinders  1 ,  2 . The IR-sensors measure without contact. In the bearing housings  3 - 6  other types of temperature gauges may be used, such as a strain gauge. In each bearing housing  3 - 6  a point of measuring  12 ,  16 ,  20 ,  21  is established. The points of measuring  13 - 21  are indicated in  FIG. 1 . In the example shown in  FIG. 1  there are six heater assemblies  23 - 28 , one at each end and one in the middle of each cylinder  1 ,  2 . The six heaters  23 - 28  are associated with one point of measuring  13 - 15 ,  17 - 19  each. A person skilled in the art realises that many different types of sensors and heater assemblies may be used. 
         [0020]    To reduce the risk of the heaters  23 - 28  influencing the sensors  11 , one or several shields  22  may be placed between the heaters and the sensors along each cylinder  1 ,  2 , as indicated in  FIG. 4 . The shields  22  will extend directed away from the cylinders  1 ,  2 . 
         [0021]    The control system of the present invention is based on the highest sensed temperature. Said highest sensed temperature will be used as set point for the other points of measuring  12 - 21 . Thus, if the sensed temperature of a specific measuring point is below the hottest sensed measuring point, the heater associated with that measuring point is activated. If the difference to the highest sensed temperature is above a predetermined value, the associated heater will be run at full effect. When the difference is below said predetermined value the heater will be run at less than 100% and will normally be controlled in such a way that the temperature of the specific measuring point will approach the established set point without exceeding it. 
         [0022]    As long as the temperatures of the points of measuring  12 - 21  are within a certain interval the cylinders  1 ,  2  will expand relatively evenly, which means that the risk of cutting of the web to be scored is reduced dramatically. A person skilled in the art realises that the temperature interval and the maximal allowed temperature difference between specific points of measuring  12 - 21  will depend on a number of factors, such as the dimensions of the cylinders  1 ,  2 , the dimensions of the cooperating projections  8  and groove  7  in the forming of the scores, the quality and material of the web, the speed of the web. 
         [0023]    In one example the heaters  23 - 28  are run at full effect if the sensed difference between a specific point of measuring  12 - 21  and the set point exceeds 2° C. When the difference is below 2° C. the specific heater  23 - 28  is controlled to let the temperature approach the set temperature without exceeding it. If the temperature in one specific point exceeds the set temperature, that higher temperature will be the new set temperature, if it still exceeds the former set temperature after a predetermined time interval. In one example this time interval was set to 8 minutes. 
         [0024]    In one other embodiment the distances between the ends of the cylinders  1 ,  2  may be altered. This is done in that either only one of the cylinders  1 ,  2  or both cylinders  1 ,  2  are arranged moveable, in relation to each other in such a way that there mutual distance is varied. Normally only one of the cylinders  1 ,  2  is arranged moveable. In this embodiment there are no heaters in the bearing housings  3 - 6 , but there are heaters along the cylinders  1 ,  2  in the same way as described above. Also in this embodiment the highest sensed temperature is the set temperature for the rest of the points of measuring  12 - 21 . 
         [0025]    The sensors  11 , heaters  23 - 28  and possible actuators to move one or both cylinders  1 ,  2  are connected to a controller, such as a computer or a CPU. The controller will hold the algorithm by which the heaters  23 - 28  and possible actuators are controlled, based on the temperatures sensed by the sensors  11 . 
         [0026]    In some embodiments fans, vortex tubes or other cooling means are placed together with the heaters  23 - 28 , in which case the temperature control may be done by a combination of heating and cooling or only by cooling. Often the cooling means are only placed at end shafts of the cylinders  1 ,  2 . 
         [0027]    The temperature range and the time interval are determined based on the dimensions of the cylinders  1 ,  2  and the scoring parts  7 ,  8  of the cylinders  1 ,  2 , on the expected temperature of the cylinders  1 ,  2  and on the quality and dimensions of the web to be scored.
     1 . cylinder (scoring cylinder)     2 . cylinder (scoring cylinder)     3 . bearing housing     4 . bearing housing     5 . bearing housing     6 . bearing housing, drive     7 . groove     8 . projection     9 . ramp     10 . IR-carbon light heater     11 . IR-sensor     12 . point of measuring     13 . point of measuring     14 . point of measuring     15 . point of measuring     16 . point of measuring     17 . point of measuring     18 . point of measuring     19 . point of measuring     20 . point of measuring     21 . point of measuring     22 . shield     23 . heater     24 . heater     25 . heater     26 . heater     27 . heater     28 . heater