Abstract:
A rope system includes an endless rope, a measuring device and a rope cutter. The endless rope is configured to travel through a machine, while the endless rope is under tension. The measuring device is used to measure the tension in the endless rope. The rope cutter is positioned to sever the endless rope if the tension exceeds a predetermined value.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a rope system and more particularly, an endless rope which is arranged to travel through a machine while being tensioned in its longitudinal direction.  
           [0003]    2. Description of the Related Art  
           [0004]    In conventional rope systems, sometimes there is a danger that a rope gets stuck or that a rope is inadvertently wrapped around a drying cylinder or around a roll. This may result in serious damage to the equipment, e.g. to the rope tensioning device or to other elements of the rope system.  
           [0005]    In the paper technology, in particular in paper or cardboard making machines or in paper or cardboard finishing machines, a rope system is often used for threading the paper or cardboard web into the machine (in particular into the drying section) when the machine is started up or after a web break. Basically, two (sometimes three) endless ropes are used which travel together along the web travel path through a drying section, a calendar section or a coating section. At the upstream end of a section, the two ropes form a rope nip. At this point, the ropes grip the beginning of an edge strip (a so-called “tail”) of the paper or cardboard web and transfer the edge strip through the section.  
           [0006]    What is needed in the art is a rope system wherein the potential of damage to the equipment is eliminated or at least reduced.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a rope system and method for using a rope system that includes a measuring device for measuring the tension value in at least one endless rope. Preferably, the tension value is measured continuously during operation of the machine.  
           [0008]    The measuring device is adapted to detect excessive tension, which is above the desired tension value normally maintained in the rope. Excessive tension may appear if the rope gets stuck or if other damage occurs to the rope system.  
           [0009]    According to one embodiment of the invention, a rope cutter is provided for severing the endless rope if the rope suddenly is excessively tensioned. The rope cutter becomes immediately active when excessive tension is detected.  
           [0010]    Generally, after severing the rope, the paper making machine is able to continue operating in the normal way because any danger of damage to the machine has been eliminated. Certainly, some loss arises from severing the rope. However, this loss is inconsequential in comparison to the damage that would occur to the mechanical equipment if the rope was not cut.  
           [0011]    Preferably, the rope system of the present invention includes a rope tensioning device with a cylinder which is adapted to move at least one sheave, that is wrapped by the rope, for tensioning the rope. A selected pressure will be supplied to the cylinder which corresponds to the desired tension value. The measuring device is adapted to measure the prevailing pressure in the cylinder. The measuring device may be embodied as a pressure switch which creates a signal if the pressure in the cylinder exceeds the selected pressure. That signal will then be transmitted to the rope cutter.  
           [0012]    In one embodiment of the invention, the rope cutter includes a cylinder for actuating the rope cutter. A control valve may be provided to control the cylinder such that the cylinder actuates the rope cutter when the signal exists. In a preferred embodiment of the invention, the control valve is controlled by a pressure fluid (e.g. compressed air) which is admitted to the control valve when the signal exists.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 shows a section of a rope system, namely a rope tensioning device including a rope cutter according to the invention; and  
         [0015]    [0015]FIG. 2 is a view along arrow II of FIG. 1. 
     
    
       [0016]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Referring now to the drawings, and more particularly to FIG. 1, there is shown a rope tensioning device  8  of the rope system including two movable sheaves  11  and  12  which support rope  9   a ,  9  and  9   b . As an example, rope  9   a  is the incoming run and rope  9   b  is the outgoing run of rope  9 . The arrangement is such that, where rope  9   a ,  9  and  9   b  wraps sheaves  11  and  12 , rope  9   a ,  9  and  9   b  form a single S (or an inverted S). Sheaves  11  and  12  are movable from an initial position, shown in full lines, away from each other, each by a distance L, into a final position as shown in dot-dash-lines, thereby extending rope  9  by a length of four times distance L.  
         [0018]    In another embodiment of the invention, the tension device may include only one movable sheave.  
         [0019]    Rope tensioning device  8  (FIGS. 1 and 2) includes a stationary frame  10  supporting two rodless pneumatic cylinders  14  and  15 . Each cylinder  14  and  15  having a movable piston (not shown) to which sheave support  13  is connected. Sheave supports  13  are adapted to support rotatable sheaves  11  and  12  (e.g. by antifriction bearings).  
         [0020]    In yet another embodiment of the invention rope tensioning device  8  will be positioned in a paper-making machine in which rope  9  is used. In the paper-making machine, the tensioning device may be arranged horizontally (as shown in FIG. 1), vertically, upside down or in any other orientation. Two or more tensioning devices may be combined in order to tension a twin-rope-system or a three-rope-system. Usually, each rope forms an endless loop traveling at the operating speed of the paper-making machine.  
         [0021]    At the infeed end of rope tensioning device  8  (close to the incoming run  9   a  of rope  9 ), rope cutter  20  is mounted on frame  10 . Rope cutter  20  includes a pivotable knife  21  which is adapted to cooperate with stationary counter knife  22 . Knife  21  is pivotable around an axle having an axis  23 . Also, knife  21  is coupled to piston  24  of a double acting pneumatic cylinder  25  which is coupled to frame  10 .  
         [0022]    A two position control valve  30  connects pressure source  31  via line  32  and  
         [0023]    either via line  26  to one side of cylinder  25  for moving (shown in the drawing) and holding knife  21  in its inoperative position as shown in FIG. 2,  
         [0024]    or via line  27  to the other side of cylinder  25  for actuating knife  21 .  
         [0025]    If knife  21  is to be actuated, valve  30  is switched over, e.g. pneumatically, by supplying pressure from pressure source  31  via line  33 , auxiliary control valve  34  and line  35  to valve  30 . This occurs if a signal is transmitted from rope tension measuring device  36  via line  37  to auxiliary control valve  34 . As an alternative, the signal may be directly transmitted from measuring device  36  via line  38  to control valve  30 .  
         [0026]    Measuring device  36  is adapted to measure the tension in rope  9 . Normally, the tension in rope  9  is held at a desired value, by maintaining a selected pressure, supplied from pressure source  19 , via line  18  to cylinder  15 .  
         [0027]    If the tension in rope  9  increases to a predetermined excessive tension value (above the desired value), resulting in increased pressure in cylinder  15  and in line  18 , measuring device  36  creates the signal to be transmitted by line  37 . As an example, measuring device  36  is designed as a pressure switch pilot valve (sometimes called “sequence valve”) which connects line  18  to line  37 . If the pressure in line  18  exceeds a certain value which can be adjusted, e.g. by setting the force of a spring  39 , the signal is generated.  
         [0028]    While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.