Abstract:
A device to provide a moment loading to one roller of a pair of nip rollers to counteract the bending moment created by a nip force between the rollers, the one roller being rotatably supported by a journal bearing at each end thereof, the device comprising a lever mechanism for imparting translational and torsional movement to the journal bearing with respect to a frame.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/170,342, filed on Apr. 17, 2009, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to laminating and printing machine rollers, and more particularly to an arrangement to prevent uneven nip force along the web due to reaction forces bending the rollers apart. 
     BACKGROUND 
     Deflection rollers are used in many printing and laminating machines. The journal ends of the shaft of the paired cylinders are mounted in journal bearings. The bearings on one or both of the cylinders are attached to a moveable arm to move the cylinders into and out of contact with each other and to set the pressure applied to the web at the nip point. The frictional driving force on the web produces an equal reaction force on the cylinders. Since the cylinder shafts are fixed at the ends, this reaction force produces a torque that increases proportional to the distance from the fixed end points, becoming greatest toward the middle and tending to causing a bend of the roller cylinders that can result in uneven nip pressure across the web. If no compensation is made to counter the roller bending, the web will be stretched at the edges more than in the center, creating a risk of tearing or wrinkling. The uneven pressure caused by the bending can also result in non-uniform transfer of ink or creases in the lamination. 
     There have been many techniques developed to compensate for the torque and reduce the bending. In heavier roller assemblies, mid-point or intermediate bearings for the shaft inside the roller cylinder may have an adjustable eccentric collar to produce a counterforce at the bearings, as described in U.S. Pat. Nos. 2,261,740 and 4,637,109. Another known technique is to pre-set a counter torque on the shaft by adjustable angle journal boxes for the shafts, for example by changing the angle of the bearings by way of adjustment screws in the bearing sleeve, as described in U.S. Pat. No. 5,052,294. The torque can also be applied by an eccentric bearing. 
     Another technique has been the use of crowned roller surfaces, where the elastic cover of the roller tapers from a higher crown in the center section to a reduced diameter toward the ends. The term “crown” is usually used to denote the shape or diameter profile of the roller necessary to compensate for deflection in order to maintain a uniform nip pressure distribution. Since roller deflection is dependant upon the roll dimensions, the elastic material, and the load applied, the crowning profile is generally matched to a particular roller configuration and constant operating loads. Common profiles can be roughly approximated using a 70 degree cosine curve to approximate the bending curve of a simple beam under uniform load. In heavier loads, rollers with long lengths may start with a longer profile up to a 90 degree cosine curve. Even after approximating the profile, however, the crown is usually adjusted by experimenting with nip impression paper to get the finished crown. 
     Since the crown profile is selected to optimize uniform pressure under a fixed set of conditions, changing the nip pressure for any reason is likely to reduce the uniformity. With relatively long slender rolls as often used in laminating machinery and some printers, it may be useful or necessary to increase the nip pressure depending upon the thickness of the laminating films or other web materials and the selected operating speed. Consequently, it would be useful to have a convenient method and versatile apparatus that can compensate for these pressure variations over a wide range of conditions. 
     BRIEF SUMMARY 
     In a pair of roller cylinders supported at each end thereof by a journal bearing attached to moveable arms for moving the cylinders into and out of contact with each other and setting the internal nip force (the pressure at the nip point), a cam and lever mechanism is provided to apply an adjustable torque to the journal bearing to produce a bending moment in the cylinders that is counter to the internal bending moment produced by the rolling contact of the cylinders. The external bending moment is proportionally adjusted when increasing or decreasing an external nip force applied to the cam and lever mechanism. The lever arm on which the cam is mounted has selectable attachment holes to increase or decrease the effective length of leverage. The bending moment can be easily set up in the static condition to accommodate variations in the thickness of the web and to then make adjustments to the internal nip force or pressure at operating speeds while maintaining the nip pressure uniformity across the roller nip axis. 
     A device is disclosed for providing a moment loading to one roller of a pair of nip rollers to counteract the bending moment created by a nip force between the rollers, the one roller being rotatably supported by a journal bearing at each end thereof. The device includes a lever mechanism for imparting translational and torsional movement to the journal bearing with respect to a frame. 
     A device is disclosed for providing a moment loading to one roller of a pair of nip rollers to counteract the bending moment created by a nip force between the rollers, the one roller being rotatably supported by a journal bearing assembly at each end thereof, the journal bearing assembly being movable with respect to a frame. The device includes a mounting arm having a journal end and a lever end, a connecting arm supported by the frame such that the connecting arm is movable in a direction substantially perpendicularly to the frame, and a lever arm pivotable about an axle supported at one end by the connecting arm and at an opposite end by the mounting arm proximal to the lever end. The journal bearing assembly is connected to the mounting arm proximal to the journal end so as to be translationally and rotationally moveable via the journal end of the mounting arm. A roller cam is rotatably supported by a first portion of the lever arm and a pull rod is supported by a second portion of the lever arm, the first and second portions of the lever arm being disposed on opposite sides of the lever arm with respect to the axle. When a force is applied to the pull rod in one direction, the lever arm forces the roller cam against the frame, thereby urging the lever end of the mounting arm away from the frame such that the journal end of the mounting arm imparts a torque to the journal bearing to increase the nip force between the rollers. 
     A method is disclosed for providing a moment loading to a pair of nip rollers that is equal and opposite to the bending moment created by the nip force between two rollers, each roller being supported at the ends thereof by journal bearings movable with respect to a frame. The method includes applying a torque to the journal bearings supporting a first one of the rollers. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a nip roller and an apparatus for controlling the roller nip force and moment loading according to the present invention. 
         FIG. 2  is an elevation partial section view of a nip roller and apparatus as in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a nip roller device  10  applied to a simple two cylinder roller system. It should be understood that web processing machinery such as printing and laminating machines many have multiple sets of rollers, some of which are pairs and others of ganged cylinders in different arrangements. For easy of understanding this invention, the device  10  is depicted as used on a sample roller pair. For purposes of this description, one of the cylinders  20  is referred to as a top cylinder and the other as a bottom cylinder  120 , although the orientation need not always be vertical. The cylinders  20 ,  120  are typically hollow. Note also that  FIG. 1  shows the rear side of a laminator machine frame  12  at one end of the roller pair. The drawing should be understood to have a similar configuration on the frame  12  at the other end of the rollers. 
     Force and torque are applied to the top cylinder  20  by actuating a bottom pull rod  32  connected via a cam and lever mechanism  22  to journal bearing assemblies  50  at either end of the cylinder  20 . In most instances, the bottom cylinder  120  will be held in a fixed position during operation of the top cylinder  20  by locking a top pull rod  132 , which is connected via a cam and lever mechanism  122  to journal bearing assemblies  150 . The static nip force and any nip force adjustments made when the web is running is usually provided through the pull rod  32 . 
     Although not depicted, it should be understood that the forces applied to the pull rods  32 ,  132  can be produced by hydraulic or other mechanical means. The forces applied by the pull rods  32 ,  132  at the ends of the cylinders  20 ,  120  is sometimes referred to as the external nip force. The reaction to the external nip force across the nip axis of the cylinders  20 ,  120  is then referred to as the internal nip force. 
     When the web is stopped, the internal nip force and external nip force are static. Once the web is in motion, these opposing forces increase due to reaction to the friction of the moving web. The effect of the static nip force applied at the ends of the cylinders  20 ,  120  and the friction component across the nip axis is well known to produce a bending moment in the shafts of the cylinders  20 ,  120  that tends to move the cylinders  20 ,  120  apart toward the middle of the nip axis. This reduced pressure in the center can cause the edges of a film web to stretch or tear, or can cause creases in the film. The device  10  solves this problem by changing the angle of the journal bearings using pull rods connected to moveable arms on which the journal bearings are mounted by a cam and lever arm arrangement. 
     In the embodiment shown in  FIG. 2 , the hollow cylinders  20 ,  120  are supported not by internal shafts but by the journal bearing assemblies  50 ,  150 , respectively. Each journal bearing  50 ,  150  includes a journal bearing sleeve  52 ,  152  and a journal bearing  54 ,  154  disposed inside an end of its respective hollow cylinder  20 ,  120 . The end of each bearing  54 ,  154  has a short journal-like shaft that extends to the sleeve  52 ,  152  holding the bearing  54 ,  154 . Alternatively, the system could use a more typical setup in which an internal shaft runs the length of each hollow cylinder  20 ,  120 , the internal shafts having journal ends that are mounted in or to journal bearings supported by journal sleeves at the ends of the hollow cylinders  20 ,  120 . In either configuration, journal ends of the cylinder  20 ,  120  are mounted in or to journal bearings  54 ,  154  and bearing sleeves  52 ,  152  forming bearing assemblies  50 ,  150  that are attached to a lever end of movable mounting arms  48 ,  148 . 
     Force to move the cylinders  20 ,  120  into and out of contact with each other and to set the static pressure at the nip point (the junction between the two roller cylinders  20 ,  120 ) is provided through pull rods  32 ,  132  connected to the respective mounting arms  48 ,  148 . In a conventional set up of this type, the pull rods  32 ,  132  would be at a fixed connection to the moveable arms  48 ,  148  so as to apply a straight line force to the arms  48 ,  148 . In the present invention, however, the pull rods  32 ,  132  are connected to the respective moveable arms  48 ,  148  by a lever mechanism  22 ,  122 , which is essentially a cam and lever arm arrangement described in more detail below, that can be used to apply a selectable torque on the journal bearing assemblies  50 ,  150  that in turn produces a bending moment on the cylinder shafts  20 ,  120 . 
     The following description of the structure of the device  10  will be done with respect to only the hollow cylinder  20 , it being understood than an identical mechanism exists with respect to the hollow cylinder  120 , as shown in the figures, with each reference numeral being identical except for being in the 100 series. 
     The lever mechanism  22  operates to apply leverage between the frame  12  and the mounting arm  48 . A bracket  40  includes an undercut groove  44   a  extending along the bracket  40  substantially perpendicularly to the frame  12 . A short connecting arm  42  extends substantially parallel to the frame  12 . The arm  42  includes a tongue  44   h  for slidingly mating with the groove  44   a  in the bracket  40  so as to permit the arm  42  to slide generally toward and away from the frame  12  while remaining substantially parallel to the frame  12 . The mating between the tongue  44   a  and groove  44   b  allows for sufficient play that the arm  42  can skew or deviate slightly from parallel to the frame  12  while still being generally constrained to move in a direction toward and away from the frame  12 . 
     An axle  36  interconnects the connecting arm  42  with a lever end of the mounting arm  48 , the lever end being at an opposite end of the mounting arm  48  from the journal end. A lever arm  24  is pivotably supported on the axle  36  between the connecting arm  42  and the mounting arm  48 . The lever arm  24  extends in both directions from the axle  36 . In one direction, a first portion of the lever arm  24  rotatably supports a roller cam  34  that engages the frame  12 . In the other direction, a second portion of the lever arm  24  includes several spaced adjustment holes  26  along its length for receiving a pin  28 . A pull rod yolk  30 , connected to and actuated by the pull rod  32 , spans the second portion of the lever arm  24 . The pin  28  connects the pull rod yolk  30  to the lever arm  24  via the holes  26  to enable the pull rod  32  to cause the lever arm  24  to pivot about the axle  36  with respect to the frame  12 . 
     In operation, the lever mechanism  22  is used to apply torque to the journal bearing assembly  50  to increase the internal roller nip force as required to maintain adequate tension across the entire film being guided through the roller pair  20 ,  120 . When an outward (tensile) external nip force is applied to the pull rod  30 , the pull rod yolk  32  and pin  28  in turn apply a pivoting force to the lever arm  24 , causing the lever arm  24  to pivot in a first direction about the axle  36 . The pivoting of the lever arm  24  forces the roller cam  34  against the frame, thereby causing an outward reaction force to be applied to the axle  36  to force the axle  36  in a direction away from the frame  12 . The outward movement of the axle  36  concomitantly moves the connecting arm  42  and the lever end of the mounting arm  48  away from the frame  12 . 
     The tongue and groove connection  44   a ,  44   b  constrains the direction of movement of the connecting arm  42  and has sufficient rigidity to balance against the torque to be applied to the bearing assembly  50 . The length of the connecting arm  42  is preferably kept as short as possible to minimize the amount of torque that must be carried by the tongue and groove connection  44   a ,  44   b . The journal end of the mounting arm  48  is constrained against movement away from the frame  12  due to its rigid connection to the bearing assembly  50 . Therefore, the journal end of the mounting arm  48  remains translationally fixed with respect to the frame  12  while the lever end, driven by the force applied via the axle  26 , is moved away from the frame  12 , thereby creating a torque on the bearing assembly  50 . 
     The torque on the bearing assembly  50 , and specifically on the bearing housing  52 , is passed to the bearing  54 , which causes a torque or bending moment to be applied to the end of the hollow cylinder  20  to create the desired internal nip force. The ratio between the external nip force applied to the pull rod  32  and the internal nip force generated by the bending moment on the roller cylinder  20  can be controlled by adjusting various parameters. In one variation, a shorter mounting arm  48  applies more torque to the bearing assembly  50  per unit movement of the axle  36  away from the frame, and a longer mounting arm  48  applies less torque. In another variation, the pin  28  connecting between the pull rod yolk  30  and the lever arm  24  can be located in one of a number of adjustment holes  26 , wherein an adjustment hole farther from the axle  36  provides for a higher ratio of internal-to-external nip force and an adjustment hole closer to the axle  36  provides for a lower ratio of internal-to-external nip force. 
     Using the device  10 , when an increased tensile force is applied to the bottom pull rod  32 , the top cylinder  20  receives both a vertical force and a torque which are transferred from the bearing assembly  50  through the journal sleeve  52  and the bearing  54  to the end of the cylinder shaft  20 . The bottom cylinder  120  reacts to the increased tensile force applied to the top pull rod  132  in a similar manner. The vertical component of the increased force to the top cylinder  20  produces a reaction force against the bottom cylinder  120  and thus against the top pull rod  132 , which in turn in turn produces a torque in the bottom cylinder bearing assembly  150  that transfers though the sleeve  152  and the bearing  154  to the journal end of the bottom cylinder  120 . These torque forces at the journal ends produce a bending moment in the cylinder shafts  20 ,  120  that can cancel out the opposite natural bending moment of the rollers  20 ,  120  and maintain uniform pressure along the nip point axis. 
     It should be clear from the above description that this cam and lever arm arrangement allows much easier adjustment of the counter bending moment than having to adjust set screws or eccentric collars or the like, and allows for adjustment to be made while the web is running. The bending moment change is proportional to the nip pressure change. The ability to change the lever arm effective length also allows a range selection of nip pressure to bending moment ratios. This allows a machine such as a film laminator to be more versatile in that it can accommodate a wide range of crowned or uncrowned rollers and web thickness, and operate effectively through a variable range of processing speeds and nip pressures.