Patent Publication Number: US-7717148-B2

Title: Machine having web tension nulling mechanism

Description:
This application is a continuation of U.S. application Ser. No. 11/006,854 filed on Dec. 8, 2004, now U.S. Pat. No. 7,267,153, which claims the benefit of U.S. application Ser. No. 60/549,518 filed on Mar. 2, 2004. The contents of all of these foregoing applications and patent are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a web tension nulling mechanism for a traveling web, so the position and alignment of the traveling web in the machine can be very precisely controlled independently of the tension, or of tension changes, in the traveling web. 
     Corrugated cardboard composite is used in a large number of applications. It is particularly desirable in packaging applications because it is rugged and has high dimensional and structural integrity. 
     A corrugated cardboard composite generally consists of first- and second-face sheets of cardboard material having a relatively flat or smooth contour, and a corrugated sheet sandwiched in between the first- and second-face sheets with the flute crests on each side of the corrugated sheet glued to the adjacent face sheet. This composite typically is made by first gluing (the flute crests on) one side of the corrugated sheet to the first-face sheet to provide a single-faced corrugated sheet or web via known or conventional techniques. This single-faced corrugated web then is fed to a corrugator glue machine, where glue is applied to the exposed flute crests of the corrugated sheet, opposite the first-face sheet, in order subsequently to bond the second-face sheet thereto, thus creating the sandwich construction described above. 
     To carry out this method, a conventional corrugator glue machine has been used for applying glue to exposed flute crests opposite the first-face sheet. Such a conventional glue machine is shown in  FIG. 1 , denoted “Prior Art.” In the conventional glue machine, labeled  10 ′ in  FIG. 1 , the traveling single-faced corrugated web  5  approaches the glue machine  10 ′ toward a delivery idler roller  12 ′. In operation, the traveling web  5  is carried around this roller  12 ′ and is delivered via a generally serpentine path to and around a web positioning roller  14 ′, such that the web  5  passes around the roller  14 ′ and through a gap  18 ′ between the web positioning roller  14 ′ and a glue applicator roller  16 ′. The web  5  is conveyed through this gap  18 ′ oriented such that the exposed flute crests  6  face the glue applicator roller  16 ′ so that glue can be applied thereto by contacting a thin glue film  4  on the outer circumferential surface of the glue applicator roll  16 ′ as the web  5  traverses the gap  18 ′. The glue film is applied to the outer surface of the applicator roller by conventional means or as described, e.g., in U.S. Pat. No. 6,602,546, which is incorporated herein by reference. Other aspects of glue application to the exposed flute crests of the single-faced web are described, e.g., in U.S. Pat. No. 6,602,546 incorporated hereinabove. For purposes of the present invention, it will be sufficient to note that the application of glue to the exposed flute crests  6  requires the gap  18 ′, and therefore the distance between the outer circumferential surfaces of the respective glue applicator roller  16 ′ and the web positioning roller  14 ′, to be precisely controlled to ensure the crests  6  contact the glue film  4  on the surface of the applicator roller  16 ′ with the appropriate amount of pressure. Too much pressure can result in crushing the flutes, and too little can result in insufficient glue application or in no glue application at all. 
     In the conventional glue machine  10 ′ shown in  FIG. 1 , both the delivery idler roller  12 ′ and the web positioning roller  14 ′ are pivotally mounted to the same support arm  20 ′, which is pivotally attached at its proximal end to a base member  40 ′ of the glue machine at pivot joint  22 ′. The reason for the pivotal attachment of the support arm  20 ′ is to permit the position of the positioning roller  14 ′ to be adjusted relative to the applicator roller  16 ′ in order to adjust the gap  18 ′ width. It will be noted that conventionally, except for axial rotation, the rollers  12 ′ and  14 ′ cannot move relative to one another. It also will be noted the rotational axis of the delivery idler roller  12 ′ is located a greater distance from the pivot joint  22 ′ than that of the positioning roller  14 ′, the significance of which will be explained below. 
     A pressure controller  50 ′ is mounted to the glue machine and is operatively coupled to the support arm  20 ′ to actuate the arm  20 ′ for regulating the width of the gap  18 ′. In this manner, the controller  50 ′ is responsible for regulating the pressure with which flutes  6  are compressed against the applicator roller  16 ′ by the positioning roller  14 ′. A significant problem in this conventional construction is that the tension of the traveling web  5  causes unequal and oppositely acting moments M 1  and M 2  at the delivery idler roller  12 ′ and the positioning roller  14 ′, respectively, to act on the support arm  20 ′ which is pivoted from a base member  40 ′ of the glue machine. The reason that moments M 1  and M 2  are unequal is that while each is the result of substantially the same net force (due to web tension), the respective lever arm lengths for each moment, measured from the pivot point of the support arm  20 ′ (pivot joint  22 ′) to the point of action of the respective moment (rotational axes of the rollers  12 ′ and  14 ′), are different. The vector sum of these unequal moments, M 1  and M 2 , is a net effective moment M 3  acting in the direction of the moment M 1 , which tends to pivot the support arm  20 ′, and therefore the positioning roller  14 ′, toward the applicator roller  16 ′. 
     As a result, the pressure controller  50 ′ must compensate for this pivot force on the positioning roller  14 ′ based on the tension in web  5  in addition to regulating the gap width to achieve optimal glue application to the flute crests  6 . This is a substantial burden on the pressure controller  50 ′ in the conventional glue machine. In addition, if there is a sudden or unpredictable change in the tension of the traveling web  5 , the pressure controller  50 ′ may not react quickly enough to compensate for the resulting change in the tension-based pivot force on the positioning roller  14 ′. The pressure controller  50 ′ also can over- or under-compensate which can result in substantial stretches of the single-faced corrugated web having too much or too little glue applied to the flutes  6 , or otherwise having the flutes  6  substantially crushed. These stretches of the web are unusable or unsaleable for the intended purpose, and contribute to substantial material waste, lost profits and/or increased price to the consumer. 
     Alternatively, in conventional glue machines  10 ′ the positioning roller  14 ′ sometimes is maintained in a fixed absolute position during operation by biasing the support arm  20 ′ toward the applicator roller  16 ′ against one or a series of hard stops using an excessive pressure or force such that web tension (or tension changes) are insufficient to counteract the biasing force and divert the fixed position of the roller  14 ′. This design is limited in that neither the width of the gap  18 ′ nor the pressure exerted by the roller  14 ′ on the flute crests  6  against the applicator roller  16 ′ can be metered or controlled during machine operation, but are fixed. 
     There is a need in the art for a mechanism or method of nulling the tension effects in the traveling single-faced web  5 , so that changes in the web tension do not effect the operation of a corrugator glue machine. Most preferably, such a mechanism or method not only will compensate out changes in the web tension, but also will compensate out the baseline or constant tension in the traveling web, so the glue machine does not need to actively compensate or account for web tension regardless of whether the tension is constant or changing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , labeled “Prior Art,” shows a side view of conventional corrugator glue machine. 
         FIG. 2  shows a side view of a corrugator glue machine according to a first embodiment of the invention. 
         FIG. 2   a  is a force-member diagram of certain members of the corrugator glue machine of  FIG. 2  superimposed over the corresponding members from  FIG. 2 , shown during operation thereof. 
         FIG. 3  shows a top perspective view of the corrugator glue machine of  FIG. 2 . 
         FIG. 4  shows a side view of a corrugator glue machine according to a second embodiment of the invention. 
     
    
    
     SUMMARY OF THE INVENTION 
     A machine is provided having an idler roller and a web positioning roller that cooperate to at least partially define a serpentine web path through the machine. A position of the positioning roller is freely adjustable within a predetermined range during operation of the machine. The machine further includes a web tension nulling mechanism effective to cancel out forces exerted on the web positioning roller resulting from tension in the web, such that these forces do not substantially affect the position of the positioning roller within the predetermined range. 
     A machine also is provided having a web positioning roller for carrying a web of material over its circumferential outer surface during operation of the machine, means for adjusting the position of the web positioning roller during operation of the machine, and a web tension nulling mechanism effective to cancel out forces exerted on the web positioning roller resulting from tension in the web, such that the adjusting means experience substantially no forces resulting from web tension. 
     A machine also is provided having a web positioning roller for carrying a web of material over its circumferential outer surface during operation of the machine, a glue applicator roller parallel to the web positioning roller and adapted to be provided with a glue film on its circumferential outer surface during operation of the machine, wherein the positioning and glue applicator rollers define a gap between their respective circumferential outer surfaces. Means also are provided for adjusting the width of the gap during operation of the machine. The machine is configured such that the gap width adjusting means experience substantially no forces resulting from web tension during operation of the machine. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     Herein, all machine elements or members, such as support arms  20   a  and  20   b , cross member  25 , etc., are considered to be rigid, substantially inelastic elements or members under the forces encountered by them in the described corrugator glue machine. All such elements or members can be made using conventional materials in a conventional manner as will be apparent to persons of ordinary skill in the art based on the present disclosure. 
     Referring now to  FIG. 2 , a first embodiment of a corrugator glue machine is shown, incorporating a web tension nulling mechanism according to the invention. The glue machine  10  includes a delivery idler roller  12 , a web positioning roller  14  and a glue applicator roller  16  substantially similar in placement as the corresponding rollers described above. In operation, the web  5  is conveyed toward and around the delivery idler roller  12 , then toward and around the web positioning roller  14  in a generally serpentine path such that, on traversing the gap  18 , the web  5  is oriented having its flutes facing the glue applicator roller  16  and is pressed up against the outer circumferential surface of that roller  16  to achieve the desired level of glue application onto the exposed flute crests  6  of the passing web  5 . 
     Still referring to  FIG. 2 , the delivery idler roller  12  is rotationally attached to a first support arm  20   a  whose proximal end is pivotally attached to a base  40  of the glue machine  10  (or to rigidly connected members which together comprise a base for the glue machine) at support pivot joint  22   a . The web positioning roller is rotationally attached to a second support arm  20   b , whose proximal end is pivotally attached to the base  40  of the glue machine  10  at a second support pivot joint  22   b . Each of the support arms  20   a  and  20   b  is independently pivotable relative to the base  40  of the glue machine about its own respective support pivot axis defined at its respective pivot joint. In an exemplary embodiment, each of the support pivot joints  22   a  and  22   b  is located or vertically aligned substantially beneath the center of gravity (axis of rotation) of the respective roller  12 ,  14  during operation of the glue machine, so the roller masses do not induce significant moments about the pivot joints in their respective support arms  20   a ,  20   b  which must be compensated for by the pressure controller  50  (described below). Alternatively, each of the support arms  20   a  and  20   b  can be pivotally attached at its proximal end at the same pivot joint (e.g. on the same shaft) or at coaxially aligned pivot joints, so long as the support arms  20   a  and  20   b  remain independently pivotable relative to one another (except as a result of the cross member  25 , described below). 
     A cross member  25  is provided extending transversely of, and linking the first and second support arms  20   a  and  20   b  as described in this paragraph. The cross member  25  is pivotally attached at its first end to the first support arm  20   a  at a first linking pivot joint  26 , and at its second end to the second support arm  20   b  at a second linking pivot joint  27 . Thus, the cross member  25  is freely pivotable relative to each of the first and second support arms  20   a  and  20   b  at the respective linking pivot joint  26 , 27 , and but for its attachment to the other support arm at its opposite end, the cross member  25  would be free to rotate about each of the linking pivot joints at each support arm. The geometry of the cross member  25  is selected based on the locations of the rotational axes of the idler and positioning rollers  12  and  14  relative to their respective support pivot joints  22   a  and  22   b  so that the greater moment generated at the idler roller  12 , compared to that generated at the positioning roller  14 , from web tension is mechanically balanced out to achieve equilibrium in both support arms based on web tension-induced forces. 
     Referring now to  FIG. 2   a , a force-member diagram is shown depicting the forces acting on the above-described mechanical system resulting from web tension as the web  5  follows the serpentine path around the idler and positioning rollers  12  and  14 . Represented in  FIG. 2   a  are the first and second support arms  20   a  and  20   b , the cross member  25  and the rollers  12  and  14 , as well as the first and second pivot joints  22   a  and  22   b , and the first and second linking pivot joints  26  and  27 . To balance out the moments generated by forces F 1  and F 2  (caused by web tension) in  FIG. 2   a , the points of attachment of the cross member  25  to the support arms (locations of first and second linking pivot joints  26  and  27 ) are selected so as to compensate out the relative mechanical advantage of the first support arm  20   a  over the second support arm  20   b  based on its longer lever arm length. 
     The following variables used in  FIG. 2   a  are defined:
         d 1 =distance from first pivot joint  22   a  to the axis of idler roller  12 ;   d 2 =distance from second pivot joint  22   b  to the axis of positioning roller  14 ;   d 3 =distance from first pivot joint  22   a  to first linking pivot joint  26 ;   d 4 =distance from second pivot joint  22   b  to second linking pivot joint  27 ;   F 1 =the force on the idler roller  12  based on web tension, which acts horizontally based on the web path;   F 2 =the force on the positioning roller  14  based on web tension, which acts horizontally based on the web path;   F 3 =the compressive force exerted by the cross member  25  on the first support arm  20   a  during operation;   F 4 =the compressive force exerted by the cross member  25  on the second support arm  20   b  during operation;   θ A =the acute angle defined between the cross member  25  and the distance d 1 ;   θ B =the acute angle defined between the cross member  25  and the distance d 2 ;   α=the interior angle between distance d 1  and the horizon; and   β=the interior angle between the distance d 2  and the horizon.       

     At equilibrium, the sum of the moments in each of the support arms  20   a  and  20   b  must equal zero. When the rollers  12  and  14  are vertically aligned over their respective support pivot joints  22   a  and  22   b  as described above, the distances d 1  and d 2  both are substantially vertical and parallel, making angles a and b both about 90°, and angles θ A  and θ B  congruent angles. Thus, for the first support arm  20   a  this gives:
 
Σ M   ARM 20a =0= F   1   d   1   −F   3   d   3   Eq. 1:
 
     For the second support arm  20   b:  
 
 ΣM   ARM 20b =0 =F   2   d   2   −F   4   d   4   Eq. 2
 
     The magnitudes of the forces F 1  and F 2  are equal because they are based on the same web tension. Also, during operation the cross member  25  is in compression due to the oppositely acting forces F 1  and F 2  tending to compress the first and second support arms  20   a  and  20   b  together, and at equilibrium the magnitudes of forces F 3  and F 4  in the cross member  25  must be equal. These relations give the following additional two equations at equilibrium:
 
F 1 =F 2   Eq. 3:
 
F 3 =F 4   Eq. 4:
 
     Substituting Eqs. 3 and 4 into Eq. 1 gives:
 
F 2 d 1 =F 4 d 3   Eq. 5:
 
     Substituting Eq. 2 into Eq. 5 gives:
 
 F   4 ( d   4   /d   2 ) d   1   =F   4   d   3   Eq. 6:
 
     Canceling the F 4  terms and rearranging gives:
 
( d   4   /d   2 )=( d   3   /d   1 )  Eq. 7:
 
     In Eq. 7 above, all the force terms cancel out, and an equilibrium condition is achieved according to the invention for the support arms  20   a  and  20   b , regardless of the web tension  5 , so long as Eq. 7 is satisfied. 
     It is desirable that each of the rollers  12  and  14  be oriented such that, when the glue machine is operating  10 , each roller&#39;s rotational axis is vertically aligned over the respective support pivot joint  22   a  or  22   b , in order to avoid any roller mass-based moments being generated in either of the support arms  20   a  or  20   b . If, for some reason, it is found to be desirable or necessary in a particular application to orient one or both of the rollers in a different geometry, then obviously the resulting mass-based moment in the affected support arm(s) will need to be taken into consideration. In addition, if the distances d 1  and d 2  are not oriented parallel, then the angles α and β will not both be 90° and angles θ A  and θ B  will not necessarily be congruent. In this case, one will need to calculate the normal force components for each of the forces F 1 -F 4  relative to the respective distance d 1  or d 2 , and use these normal force component values to solve an analogous system of equations as above to determine the appropriate geometry for the cross member  25  in a particular installation. Such trigonometric calculations can be performed by the person of ordinary skill in the art for a given system without undue experimentation. 
     It will be understood to those of ordinary skill in the art that each of the distances d 1 -d 4  referred to above is to be measured as the linear distance between the respectively defined points, and not necessarily as the length of any actual member. For example, d 1  is the linear distance between the first pivot joint  22   a  (pivot axis) and the axis of rotation of the delivery idler roller  12 ; d 2  is the linear distance between the second pivot joint  22   b  (pivot axis) and the axis of rotation of the web positioning roller  14 ; d 3  is the linear distance between the axes of the first pivot joint  22   a  and the first linking pivot joint  26 ; and d 4  is the linear distance between the axes of the second pivot joint  22   b  and the second linking pivot joint  27 . This is so regardless of the actual path or shape of the respective first and second support arms  20   a  and  20   b  which may be straight or curved members. Also herein, when referring to the arms  20   a  and  20   b  as being parallel or substantially parallel, it will be understood that what is being referred to are imaginary lines drawn along the respective distances d 1  for the first support arm  20   a  and d 2  for the second support arm  20   b . Where the support arms  20   a  and  20   b  are straight members, these imaginary lines will become substantially colinear with their support arms, and the distinction between the actual support arm and the respective linear distance between two points on that arm will be diminished. However, if the support arms are to be curved members, then parallelism of the support arms, as well as the angles θ A  and θ B , must be measured relative to the linear distances d 1  and d 2  respectively, as they are described in this paragraph. 
     It is noted once again that all of the actual force terms (F 1 -F 4 ) drop out of Eq. 7 above. As a result, not only is the mechanism according to the invention effective to null out web tension effects based on a constant tension in the web  5 , but also changes, even unexpected or sudden changes, in web tension due to factors external to the glue machine  10  do not compromise or substantially compromise the equilibrium (based on web tension effects) established by cross member  25  between the first and second support arms  20   a  and  20   b  in the glue machine for supporting the idler and positioning rollers  12  and  14 . Consequently, the absolute position of the positioning roller  14  need not be fixed during operation of the machine  10  in order to prevent its being acted on by web tension-induced forces or moments, and, according to the invention, the roller  14  is permitted to float freely within a predetermined range in an arc about its support pivot joint  22   b  during operation of the glue machine. Thus, the roller  14  is freely adjustable within this predetermined range during operation of the glue machine. 
     A pressure or gap metering controller  50  is coupled to the second support arm  20   b  as shown in  FIGS. 2 and 4 , which otherwise is freely adjustable during machine operation as described in the preceding paragraph. The controller  50  is capable of precisely metering the width of the gap  18  between the positioning and applicator rollers  14  and  16 , and/or the pressure exerted by the roller  14  on the flutes against the applicator roller  16  to achieve optimal glue application to the passing flute crests  6 . The pressure controller  50  does not have to compensate or account for tension in the web  5 , nor is its operation or the precise metering of gap  18  substantially disturbed or affected due to even significant sudden or unpredictable changes in web tension. This presents several significant advantages over conventional glue machines. First, the pressure controller  50  can incorporate very high precision motors, servos, pneumatic cylinders, or the like, or suitable combinations of these or other conventional mechanical or pneumatic or hydraulic metering devices, to achieve very high precision metering of the position of roller  14  as well as the pressure exerted thereby on the web  5  against the applicator roller  16 , to provide precise dynamic gap metering control for a wide range of different flute sizes (e.g., sizes A through E or smaller) to achieve optimal glue-to-flute application. Conventionally, very high precision metering components for the controller  50  were problematic due to relatively large web tension-effect forces, as well as sudden significant changes in such forces, that the controller  50  had to withstand and compensate for. Because these large magnitude forces have been mechanically nulled or compensated out according to the invention, higher precision and more sensitive metering devices can be used in the pressure controller  50  than were previously possible, and a machine according to the invention provides very precise dynamic gap metering control independent of web tension effects. 
     Second, large stretches of unusable web material associated with over- or under-compensation of the pressure controller  50  due to sudden or unexpected changes in web tension are substantially eliminated, because such changes no longer substantially affect or induce net forces exerted on the positioning roller  14  or the controller  50 . Optionally, the pressure controller  50  can be coupled to the first support arm  20   a  in order to regulate the width of the gap  18 , though this is less preferred. 
     Those of ordinary skill in the art will appreciate that when the rotational axes of the idler and positioning rollers  12  and  14  are aligned directly over their respective support pivot joints  22   a  and  22   b  in respective vertical planes, the masses of these rollers contribute zero moment to the support arms  20   a  and  20   b  that must be accounted for by the controller  50 . However, during operation it is recognized that to the extent the positioning roller  14 , and therefore also the idler roller  12  (assuming the distances d 1  and d 2  to be parallel), are adjusted to a position outside of its respective vertical plane with the associated support pivot joint  22   a , 22   b , then the controller  50  will need to account for the resulting moments induced in the support arms  20   a  and  20   b  in order to counteract their effect on the desired position of the roller  14 . This does not introduce a significant challenge to the design of the controller  50  because the resulting moments, and more importantly the force necessary to counteract them, are known or derivable functions of the position of the positioning roller  14  based on the masses of the rollers  12 , 14  and the geometry of the system, all of which are known variables for a given machine  10 . The nulling mechanism according to the invention as illustrated, e.g., in the disclosed embodiments, is effective to counteract or substantially null out forces and moments exerted on machine members (such as rollers  12 , 14 , and support arms  20   a , 20   b ) resulting from tension in the traveling web  5 , so these forces do not affect the position of the roller  14  within the predetermined range described above. With these forces canceled out, the controller  50  can provide effective metering of the gap  18  during operation of the glue machine  10  that takes into account and compensates against the predictable forces resulting from roller-mass induced moments based on the relative position of the positioning roller  14  within the predetermined range. 
     That predetermined range may vary based on the machine and its particular application, but generally will be broad enough to accommodate a wide range of flute sizes, as well as a broad range of compression rates for each flute size that is to be compatible with the glue machine. The predetermined range can be, for example, an arc length of up to at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, inches, with the controller  50  capable to maintain precise dynamic gap metering control within such range. 
     It will be understood that  FIG. 2  is a side view, and that typically the glue machine  10  will have two “first” support arms  20   a  located at opposite ends of the laterally extending delivery idler roller  12 , as well as two “second” support arms  20   b  located at opposite ends of the laterally extending web positioning roller  14  (see  FIG. 3 ). In the illustrated embodiment, each of the rollers  12  and  14  is rotationally supported on a respective axially extending lateral shaft  31 , 32  that is supported at its opposite ends on the paired “first” support arms  20   a  or the paired “second” support arms  20   b  as shown in  FIG. 3 . In this embodiment, a suitable cross member  25  is provided linking both sets of the adjacent first and second support arms  20   a  and  20   b  located on either side of the glue machine  10 , with each cross member  25  having suitable geometry as described above to null out web tension effects. Alternatively, the glue machine can be provided such that each of the rollers  12  and  14  is rotationally supported on a shaft that is cantilevered from a single support arm, such as the respective first and second support arms  20   a  and  20   b  shown in  FIG. 2 , located on only one side of the machine. In this case, a cross member  25  is provided on only one side of the machine  10  linking the first and second support arms  20   a  and  20   b.    
     In  FIG. 2 , both the first and second support arms  20   a  and  20   b  are anchored to the base  40  of the glue machine  10  at respective pivot joints  22   a  and  22   b  located in substantially the same horizontal plane; i.e. they are at substantially the same elevation. However, this is not required. As seen in  FIG. 4 , it is permissible, and in some cases it is preferred, to anchor the second support arm  20   b  to the machine base  40  at a pivot joint located at an elevation different from that of the first support arm  20   a . As evident by comparing  FIG. 2  and  FIG. 4 , this will result in the cross member  25  having a different slope between the respective first and second linking pivot joints  26  and  27 , assuming the relative positions of the rollers  12  and  14  do not change. However, so long as Eq. 7 (assuming the support arms  20   a  and  20   b  are parallel) is satisfied, the resulting mechanism will be effective to null out web tension effects so they do not cause any net force to be exerted on the positioning roller  14 , and consequently they will not affect the pressure controller&#39;s ability to precisely meter the width of the gap  18  as glue is being applied to the passing flute crests  6 . 
     Thus, it will be understood from the foregoing description that according to the invention, the geometries of the first and second support arms  20   a  and  20   b , the cross member  25 , the first and second pivot joints  22   a  and  22   b  and the first and second linking pivot joints  26  and  27 , all cooperate to provide an effective web tension nulling mechanism such that web tension-effect forces on the respective idler and positioning rollers  12  and  14  are effectively canceled out. In other words, the geometry of the elements mentioned in this paragraph is selected according to the invention such that the moments acting on the first and second support arms  20   a  and  20   b , based on the tension in the web  5  acting through contact with the rollers  12  and  14 , are effectively mechanically canceled out so that their vector sum is equal or substantially equal to zero. It will be seen from the foregoing explanation that the cross member  25  dynamically links the rollers  12  and  14  in a manner so as to achieve this effect. (By “dynamically links,” it is meant that the rollers  12  and  14  are linked through a series of intermediately linked machine members or elements so that their relative positions are not static; i.e. they are movable relative to one another to a degree permitted by the intermediate elements). As a result, any change in the tension of traveling web  5  will result in corresponding equal changes in the magnitudes of the oppositely acting moments in the respective first and second support arms  20   a  and  20   b , the net effect being that these moments mechanically cancel out resulting in a net zero change in the position of the positioning roller  14  due to transient web tension effects. Consequently, the pressure controller experiences no or substantially no net forces as a result of web tension effects, which is then responsible solely for regulating the gap  18  width (and for compensating predictable roller mass-based moments). 
     This is especially important when changing flute sizes in the glue machine. It is important to accurately meter the width of the gap  18  and the pressure exerted by the positioning roller  14  against the flutes  6  (against applicator roller  16 ) to ensure the correct amount of glue is applied across different flute sizes when such different sizes are used. 
     The glue machine according to the invention, incorporating the above-described web tension nulling geometry, allows very precise metering of the gap  18  regardless and independent of the web tension, or of sudden changes in the web tension based on external factors beyond the scope of the glue machine. 
     The above description of the web tension nulling mechanism has been provided with respect to a transversely extending cross member  25  pivotally linked to first and second support arms  20   a  and  20   b , which in turn support the idler roller  12  and web positioning roller  14 . However, the nulling mechanism according to the invention is not to be correspondingly limited to this construction. For example, it is possible and contemplated that linkage systems comprising a plurality of members can be incorporated to dynamically link the idler and positioning rollers  12  and  14 , or the first and second support arms  20   a  and  20   b , so as to effectively cancel out the web tension-induced forces as described herein; the invention is not limited to a single cross member  25 . Also, it will be evident to the person of ordinary skill in the art, on reading the present disclosure, that other mechanical linkages or linkage systems can be established to achieve the web tension nulling effect as described, herein, so that the controller  50  that is operatively coupled to the positioning roller  14  is shielded from web tension-induced forces during operation of the glue machine  10 . It is contemplated that the present invention encompasses all such mechanical linkages and linkage systems. The constructions disclosed herein are provided to illustrate exemplary embodiments of the invention. 
     It is to be noted that precise gap metering control has been described above with respect to adjusting the position of the web positioning roller  14 . Alternatively, it is contemplated that gap metering control can be achieved by fixing the position of the positioning roller  14  and adjusting the position of the glue roller  16 . This construction, however, is less preferred because of the relative complexity associated with adjusting the position of the glue applicator roller  16  during machine operation. For example, the thickness of the glue film  4  applied to the circumferential surface of the applicator roller  16  also typically is precisely metered to achieve optimal glue application, e.g., by the methods described in U.S. Pat. No. 6,602,546 incorporated hereinabove. Thus, in order to adjust the relative position of the applicator roller  16 , the relative positions of a substantial number of additional machine components also would need to be correspondingly adjusted, such as the glue tray and isobar assemblies described in that patent. For example, one method would be to incorporate all of the applicator roller-associated components onto a subassembly and to provide a rail system for translating the subassembly relative to the positioning roller  14 . However, adjustment in this manner may compromise the precision of the glue film application components, as well as contribute excessive complexity and cost to the machine&#39;s manufacture. For at least these reasons, it is preferred to adjust the position of the positioning roller  14  relative to that of the applicator roller  16  whose position is fixed on a stationary rotational axis, and to mechanically cancel out web tension-induced forces acting on the positioning roller, or on any of its associated linkages, by incorporating a web tension nulling mechanism as disclosed herein. 
     Though the web tension nulling mechanism has been described herein with respect to its application in a corrugator glue machine  10 , the basic invention can be applied to null or cancel out transient web tension effects in any processing unit or other machine that carries or operates on a traveling material web. A person of ordinary skill in the art, based on the present disclosure, will be able to adapt the teachings of this document to provide an effective web tension nulling mechanism to other such processing units or machines without undue experimentation. 
     Although the invention has been described with respect to certain embodiments, it will be understood that various changes or modifications can be made thereto based on the present disclosure without departing from the spirit and the scope of the invention as set forth in the appended claims.