Abstract:
A reel-up having pivoting first members mounted on carriages where the first members engage the bearing housings of a reel spool. The first members are mounted between stops which limit their maximum deflection. A load cell is positioned on each carriage, the pivoting first members being between the load cell and the reel spool bearing housings. The load cells and the flexibility of the pivoting first members are selected so that each first member bottoms out on a stop before the load cell is subjected to more than its design load.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to reel-ups which operate on papermaking machines in general, and more particularly to force sensors which measure the nip loading between a reeling cylinder and a forming paper parent reel. 
   Paper which is made on a papermaking machine is wound up into reels which are periodically removed from the papermaking machine for further processing. The reels are large, sometimes 10 m in length and 3 or 4 m in diameter and weighing over 120 tons. To maintain the quality of the paper wound into the reel, the formation of the reel must be carefully controlled. There are three primary factors which control the quality of the reel formed, these are: the web tension, the center wind assist torque, and—most importantly—the nip loading between the paper reel and the reeling cylinder. The reeling cylinder is a roll drum which is normally driven and which is positioned just before the reel. The paper web typically wraps part of the reeling cylinder and then enters a nip formed between the reeling cylinder and a forming paper reel, and is wound onto the paper reel. It is the loading of this nip formed between the reeling cylinder and the paper reel which must be controlled to maximize the quality of the paper reel formed. The nip loading will typically be varied, typically decreasing in magnitude as the size of the paper reel increases. 
   The reel-up process begins with an empty spool or reel core which is brought down from a storage unit positioned above the reeling cylinder and into engagement with the reeling cylinder—typically on a pair of rotating arms which terminate in forks which extend on either side of the reel core bearings. The web is transferred from a fully formed paper reel to the empty spool or reel core in a process known as the reel change-over. Immediately, or once the paper reel has reached a given size, the roll spool is positioned between a pair of carriages which ride on level rails. The reel spool rotates freely on bearings contained within bearing housings. The bearing housings in turn are supported by the carriages which are movable on the horizontal rails. Web tension is controlled by the reeling cylinder, and torque is applied to the reel spool via center wind assist. Nip load is controlled by hydraulic cylinders which position the carriages on which the bearing housings and thus the paper reel are supported. The hydraulic cylinders adjust the position of the paper reel to control the nip loading of the paper reel with the reeling cylinder. Nip pressure may be monitored by monitoring the pressure in the hydraulic cylinders which position the carriages. More recently, load cells have been incorporated in the pins which join the hydraulic cylinders to the carriages. Although the use of load cells is superior to measuring hydraulic cylinder pressure, the use of load cells would benefit from more accurate determination of nip loading. What is needed is a load cell arrangement where load cells of smaller range and more accurate output can be used. 
   SUMMARY OF THE INVENTION 
   The reel-up of this invention employs pivoting arms mounted on a carriage which engages the bearing housings of a reel spool. The arms are mounted between stops so the maximum deflection of the pivoting arms is limited by the stops. A load cell is positioned on the carriage with a pivoting arm between the load cell and the reel spool bearing housings. The load cell, and the flexibility of the pivot arm are selected so that the pivot arm bottoms out on a stop before the load cell is subjected to more than its design load. In prior art designs the load cell was considerably over designed because it could be subjected to loads many times higher than the nip loading forces. Because load cell accuracy is a fraction of total load cell range, nip loading suffered from a lack of accuracy because only a small percentage of the load cell&#39;s range was employed during normal nip loading. The load cell of the current invention is selected to have a range up to only the maximum nip load used by the reel-up. 
   It is a feature of the present invention to provide a reel-up which forms paper reels of improved quality. 
   It is another feature the present invention to provide a reel-up which can more precisely control the nip pressure used in forming the paper reel. 
   Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is simplified side elevational view of a paper reel-up incorporating the load cell mounting arrangement of this invention. 
       FIG. 2  is a detailed view of the load cell mounting arrangement of FIG.  1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring more particularly to  FIGS. 1-2 , wherein like numbers refer to similar parts, a reel-up  20  is shown in FIG.  1 . The reel-up  20  receives a paper web  22  from a papermaking machine (not shown) which travels over the reeling cylinder  24  mounted reel-up frame  25  to a nip  26  formed with a parent reel  28 . The paper web  22  is then wound on to the parent reel  28 . The parent reel  28  is formed about a reel spool  30  which is moved from a reel spool storage (not shown) into engagement with the reeling cylinder  24  between a pair of primary arms  32 . Although only one primary arm  32  is shown in the figures, it will be understood that the structures described herein will be substantially duplicated with respect to the front and back of the reel-up  20 . The primary arms  32  have opposed grippers  34  which hold the reel spool bearing housings  36 . 
   The primary arms  32  transport the reel spool  30  to horizontal support rails  38 , shown in  FIG. 1 , where the bearing housings  36  are received by carriages  40 . The position of the carriages  40  is controlled by hydraulic actuators  42  which position the reel spool  30  with respect to the reeling cylinder  24 , and directly control the nip pressure formed in the nip  26  between the forming parent roll  28  and the reeling cylinder  24 . 
   Each carriage  40  has a first arm  46  and a second arm  48  which together engage a roll bearing housing  36  which carries the reel spool  30 . The first arm  46  is on the side of the reel spool  30  facing the reeling cylinder  24 , while the second arm  48  is on the opposite side of the reel spool. The reel spool  30  is held on the carriages by the roll bearing housings  36  between first arms  46 , and second arms  48  which are positioned opposite the first arms  46 . The operation of a carriage with arms that engage a roll bearing housing is described more fully in U.S. Pat. No. 6,036,137 to Myren and U.S. Pat. No. 6,550,713 to Ruha et al. which are incorporated herein by reference. 
   As best shown in  FIG. 2 , each second arm  48  incorporates a rotating first member  50  which is mounted by a pivot bearing  52  to the carriage  40 . Each rotating first member  50  extends upwardly from a pivot  52  between an upstream stop  54  mounted to the structure of the second arm  48  and a downstream stop  56  also mounted to the structure of the second arm  48 . A load cell  58  is mounted to a bracket  59  on the second carriage arm  48  opposite the downstream side  60  of the rotating first member  50 . 
   When the parent reel  28  is urged against the reeling cylinder  24  by the operation of the hydraulic actuators  42  a force is applied at the nip  26 . The force applied at the nip  26  is nearly identical to the force applied to the first members  50 . The weight of the parent reel  28  is supported by the bearing housings  36  on the support rails  38 . And the only lateral force applied to the parent reel  28  is where the first members  50  engage the roll bearing housings  36 . Hence it is possible to determine the nip force by determining the force on the load cells  58  positioned on the second arm  48 . 
   Each load cell  58  is positioned to be engaged by a rotating first member  50  as the member  50  moves toward the downstream stop  56 . Load cells are typically designed with relatively little deflection so that deflection of the load cell does not affect the mechanical properties of the mechanical system in which it is incorporated. Thus a load cell can be used to replace a substantially rigid support, or is designed to replace a pin or a bolt in a mechanical linkage while preserving the properties of the bolt or support which deflect little under load. Although the stiffness of the load cell is an advantage in designing load cells into structures, this feature has the disadvantage that if the structure is subjected to transitory loads caused, for example, by one part hitting or coming to a sudden stop against another, the capabilities of the load cell must be large or the limits of the load cell may be exceeded by the transitory loads, this can have detrimental effects on the reliability and accuracy of the load cell. 
   The rotating first member  50  is used to limit the loading on the load cell  58 . The rotating first member  50  has a pivot base  62  with a cantilevered beam  64  extending from the base. The cantilevered beam  64  extends between the pivot base  62  which is mounted to the pivot  52  and the reel spool bearing housing  36  or the downstream stop  56 . By design choice, the cantilevered beam  64  forms a flexible member or flexible portion of the rotating member, which portion has a selected amount of beam flexure so as to allow significant deflection of the beam  64  as the load cell  58  is loaded. The beam  64  is designed with a spring constant such that elastic deflection of the beam between the point when the beam  64  first engages the load cell  58  and where the beam  64  engages the downstream stop  56  produces a force on the load cell which is less than its maximum load measuring capability or range. The downstream stop  56  together with the position of the load cell  58  sets the maximum deflection to which the cantilevered beam  64  of the rotating first member  50  can be subjected. The maximum deflection of the cantilevered beam  64  in turn sets the maximum load which can be applied to the load cell  58 . The cantilevered beam  64  can apply a certain amount of mechanical advantage depending on the position of the load cell between the pivot  52  and the roll bearing housing  36  contact point  66 . For example, if the load cell is positioned halfway between the contact point  66  and the pivot  52 , the force applied by the first member  50  to the load cell  58  would be twice that applied to the bearing housing  36 . 
   In one known application of a load cell used to measure paper reel nip load, a 100 kN measuring load cell is used to measure a loading force of about 8 kN. The prior art load cell is incorporated in the pin conection where the hydraulic actuator  42  joins the carriage  40 . If the load cell drifts even 1 percent a considerable error, of about 10 percent in the measured nip force will result. The load cell  58  can have a maximum range which approximately matches or is slight greater than the applied load. Depending on the mechanical advantage applied by the rotating first member  50 , the load cell could be a range of values, but in all cases because the applied load is matched to the load cell maximum range, load cell drift will be considerably smaller in proportion to the total load measured. Another problem is that friction of the linear bearing where the carriage  40  slides on the horizontal support rails  38  also affects the load in the nip  26 , however the output of the prior art load cell located between the hydraulic actuator  42  and the carriage  40  does not measure the carriage friction loads. The location of the load cell  58  of this invention measures the forces applied directly to the roll bearing housings of the reel spool which includes the force of the hydraulic actuators  42  and the carriage friction loads. 
   Accurate measurement of nip force loads is particularly important with paper grades that cannot handle high nip loading, such as tissue paper and release paper. Another advantage of the load cell  58  and its mounting position is that less disassembly of the carriage  40  is required to change a damaged or defective load cell. Measurement of the zero point and gain for the sensor is easier to check and adjust because the sensor is not part of the basic carriage structure. 
   It should be understood that the load cell arrangement described hearin could be used with a wide range of reel-up designs, but may be particularly advantageously used with those designs sold under the trademarks OptiReel™, and OptiReel™, M model, sold by Metso Paper, Inc., but could be used with the Beloit style TNT reel such as disclosed in U.S. Pat. No. 5,370,327, or conventional Pope style reels or ValReel™ available from Metso Paper, Inc. where the carriage which holds the reel spool may be fixedly mounted to pivoting arms. For example the primary arms  32 , which terminate in two grippers  34  can be considered carriages and could incorporate the load measuring structure of this invention. It should be understood that the load cell  58  could be of any design which meets the required performance criteria, for example, model LBM series load buttons available from Interface, Inc. of Scottsdale, Ariz., can be used. 
   It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.