Abstract:
An improved sheeter wire device providing constant tension on a feeder spool even during wire breakage. A constant speed motor draws wire across the face of the sheeter while a drag motor maintains constant tension on the wire. A pair of pinch rollers prohibits unwinding of the feeder spool in the event of wire breakage.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an improved sheeter wire apparatus and, in particular, to a sheeter wire apparatus which provides for a continuous advancement of sheeter wire using a simple design that provides constant tension on the feed spool even during wire breakage. This is accomplished by the use of a drag motor connected to the supply spool, a constant speed motor connected the take-up spool, and a feed spool tension device. 
     2. Description of Related Art 
     A sheeter is a device commonly used in the food industry for making flattened food products, such as tortilla chips, in a continuous processing operation. Typically, a dough product is compressed between a pair of counter rotating sheeter rollers that are located closely together, thereby providing a pinch point through which the dough is formed into sheets. The dough can then be cut by, for example, a cutting roller to form the shape of the product desired. 
     Many dough products, particularly those that are corn based (“masa”), have a tendency to stick to the sheeter rollers rather than dropping onto a conveyer for transportation to the next processing step, such as a baking oven. One common approach to this problem is to string a stripper wire across the face of the sheeter roller so that the stripper wire can scrap away the dough product off of the surface of the roller. 
     An example of a prior art design in this regard is illustrated by FIG.  1 . FIG. 1 is a perspective view of the output of a dough sheeter device  110 . The cut dough product, in this case uncooked tortilla chips  120  made from masa, can be seen on a conveyer  130  after being deposited on the conveyer  130  by a sheeter roller  140 . The sheeter roller  140  will typically have plurality of plastic bands  150  about the circumference of the sheeter roller  140 . These bands  150  ride in groves (now shown) in the sheeter roller  140  and hold the sheeter wire  160  close to the surface of the sheeter roller  140 . The bands  150  also provide a surface for returning ribbons of unused masa to the sheeter  110 . A sheeter wire  160  is shown strung across the face of the sheeter roller  140 . This sheeter wire  160  is attached to two fixed points  170 ,  180  and is threaded across the face of the sheeter roller  140  underneath each of the bands  150 . This provides a flush contact between the sheeter wire  160  and the surface of the sheeter roller  140 . 
     Also shown is a tension device  190 , which can be a hydraulic or pneumatic device that provides a constant tension on the wire  160 . This tension device  190  is typically connected to a warning device to provide an indication of wire breakage. Alternatively, the tension device  190  can also act as the second fixed point, thereby eliminating the post  180  shown in FIG.  1 . FIG. 1 shows the sheeter wire  160  on the front or open side of the sheeter roller  140 . The sheeter wire  160  can also be located in the same relative vertical position but on the back, or concealed, side of the roller  140 . 
     The sheeter wire  160  is typically commercial piano wire. A typical tension on the wire during operation is 100 to 125 pounds. Contact with hardened masa, particularly during start-up, can subject the sheeter wire  160  to higher tension for short time periods. During operation the wire is also subject to friction from the moving face of the sheeter roller  140 . The wire  160  must be replaced periodically or it is prone to breakage after time. In fact, in a continuous use operation for a typical sheeter device producing tortilla chips, it has been observed that such fixed sheeter wire  160  will break, if not replaced, nearly daily. 
     In order to replace a broken sheeter wire  160  the entire sheeter device  110  and, consequently, the entire chip processing assembly, must be stopped. The old sheeter wire  160  is removed. A new sheeter wire  160  is attached to the first attaching point  170 , strung across the face of the sheeter roller  140  under the bands  150 , and attached to a second attaching point  180 . Then the tension device  190  must be reactivated. Raw material is lost because the dough that was on the sheeter must be thrown away and additional product downstream my need to be discarded. In addition, line start-up procedures must be initiated, which usually results in the loss of further product. A wire breakage event, therefore, results in a substantial amount of unscheduled downtime and lost product. The alternative is to schedule, on a daily basis, the replacement of the sheeter wire  160 . A scheduled replacement of the sheeter wire  160 , however, results in even more frequent, although scheduled, downtime. 
     One attempt at addressing the wire breakage problem is reflected in U.S. Pat. No. 5,720,990 (“Lawrence”) issued on Feb. 24, 1998. The Lawrence patent discloses a wire separator system for a sheeter device comprising a motor that drives a feed spool and a motor that drives a take-up spool. Tension is maintained on the sheeter wire by use of a tension sensing pulley providing input to a controller which modulates the torque on the take-up reel. Provided that the wire does not unexpectedly break, the Lawrence patent discloses a device that will allow the sheeter to run for long periods of time without the necessity of stopping the sheeter to replace the sheeter wire, because new wire is constantly drawn across the contact surface. 
     The invention disclosed by Lawrence has several drawbacks, however. First, the design assumes that the wire will not break during operation. Unfortunately, this is not a safe assumption. In fact, it is not an infrequent occurrence that wire breakage occurs on the prior art model illustrated by FIG. 1 shortly after a new wire has been installed. This could occur due to a sudden contact with a dried piece of dough that has become affixed to the sheeter while the sheeter is stationary. Further, an initial steady-state friction between the sheeter wire and the sheeter must be overcome at the instant the sheeter begins to rotate. Since the Lawrence device provides that one motor feeds wire while another motor takes-up wire, a breakage between the two motors can result in the continued feeding of wire into the sheeter until the feed motor comes to a stop. A breakage also results in a loss of tension on the feed spool and can lead to unraveling or the “weed eater” effect, whereby the spool becomes unwound. Further, the Lawrence device is designed to maintain constant tension of the wire by using a variable speed pulling motor connected to the take-up reel. Since the Lawrence feed spool is connected to a fixed speed motor, the tension will necessarily fluctuate at the point that the wire is leaving the feed spool when, for example, the wire encounters a piece of dried dough product on the sheeter during operation. These torque fluctuations could effect the consistency of the feed spool&#39;s wound tension, thereby leading to further torque fluctuations and potential feed problems. 
     Consequently, a need exists for an improved continuous sheeter wire apparatus that maintains a constant tension on the feed spool even during wire breakage. This apparatus should be designed, in a fail safe way, to avoid driving sheeter wire into the sheeter after a wire breakage. The improved apparatus should also be of a relatively simple design with a minimum number of necessary and washable components. 
     SUMMARY OF THE INVENTION 
     The proposed invention comprises an improved continuous sheeter wire apparatus that uses a drag motor to control constant tension on the feed spool and a constant velocity motor driving the take-up spool. The invention also incorporates pinch rollers on the feed spool to insure that, even during wire breakage, constant tension is maintained. 
     In use, the constant speed motor pulls wire onto the take-up spool. Constant tension is maintained on the sheeter wire by the torque of the drag motor connected to the feed spool. Since tension is controlled at the feed end of the device, as opposed to the take-up end, minor tension fluctuations will be experienced by the take-up spool as opposed to the feed spool. This keeps the wire wound consistently on the feed spool. Since, in the event of wire breakage, the wire on the take-up spool will be discarded, winding variations due to minor tension variations on the take-up spool are inconsequential. 
     In the event of wire breakage, there is no possibility of feed wire being driven into the sheeter, since the feed spool is connected to a drag motor. A loss of torque on the drag motor is sensed and the entire sheeter assembly is shut down. Further, pinch rollers insure that there is no loss of tension on the feed spool itself, thereby avoiding unraveling of this spool or the “weed eater” effect. 
     The above as well as additional features and advantages of the present invention will become apparent in the following written detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective representation of a prior art sheeter device with a fixed sheeter wire; 
     FIG. 2 is a perspective representation of one embodiment of the invention; 
     FIG. 3 is a schematic side view representation of one embodiment of the invention; and, 
     FIG. 4 is a perspective view of the feeder spool and spool tension device of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 shows one embodiment of the present invention installed on a sheeter device  210 . Shown are the bands  250 , sheeter roller  240 , conveyer  230 , and a resultant product  220 . Rather than affixing the sheeter wire  260  in a stationary position, however, the present invention provides for a constant speed motor  288  which reels the sheeter wire  260  onto a take-up spool  284 . The sheeter wire  260  is dispensed from a feed spool  282 , which is connected to a drag motor  286 . The drag motor  286  is set for a specific constant torque which insures that the tension on the sheeter wire  260  is always constant near the feed spool  282 . From the feed spool  282 , the sheeter wire  260  is threaded past a post or pulley  292 . As with prior art designs, the sheeter wire  260  is then strung across the face of the sheeter roller  240  by threading the sheeter wire  260  under the several bands  250 . The sheeter wire  260  is then strung across a second post or pulley  294  before being attached to the take-up spool  284 . FIG. 2 also shows two opposed pinch rollers  296 ,  297 , which are addressed in more detail in FIG.  4 . 
     FIG. 3 is a schematic side view of the present invention in operation in conjunction with a sheeter device. Masa  346  is fed between a press roller  342  and the sheeter roller  340 . The press roller  342  turns at a slower rotational speed than the sheeter roller  340 . This results in the masa adhering to the sheeter roller  340 . The masa  346  is next cut by a cutter roller  344 . The cut masa is then stripped from the sheeter roller  340  by the sheeter wire  360 , which is being slowly pulled across the face of the sheeter roller  340 . The cut product  320  then drops onto a conveyer  330  to be transported for further processing. As with the prior art devices illustrated in FIG. 1, the location of the sheeter wire  360  can be on the front of the sheeter roller  340  (as illustrated) or on the back of the sheeter roller  340  immediately downstream of the cutter roller 
     FIG. 4 illustrates one embodiment of a pinch roller design that provides a constant tension on the feed spool in the event of wire breakage. The feed spool  482  is mounted on a shaft  494  connected to the drag motor  486 . Two spring-loaded pinch rollers  496 ,  497  are then placed in pressure contact with the feed spool  482 . As the sheeter wire  460  is dispensed from the feed spool  482 , the pinch rollers  496 ,  497  ride along the surface of the feed spool  482 . If the sheeter wire  460  were to break, the drag motor  486  would stop and the sheeter wire  460  would be held in place on the feed spool  482 , thereby prohibiting unraveling of the feed spool  482  by the stationary pinch rollers  496 ,  497 . 
     The feed spool  482  can be removed from the shaft  494  by spreading apart the pinch rollers  496 ,  497  and pulling the feed spool  482  off of the shaft  494 . It should be understood that while the embodiment illustrated in FIG. 4 shows two pinch rollers  496 ,  497 , it is contemplated that the invention might utilize any number of roller designs, including a single stationary roller riding on the surface of the wire wound around the feed spool  482 , as long as the design provides adequate pressure on the surface of the feed spool  482  while also allowing the sheeter wire  460  to be dispensed from the feed spool  482  during continuous operation. 
     As can be seen by FIG. 2, the invention is simple in design and in use. Using a drag motor  286  to regulate tension on the feed spool  282  is a fail safe method of insuring that the sheeter wire  260  will not be fed into the sheeter  210  in the event of a wire breakage event. The drag motor  286  is electrically connected to a controller (not shown). When the controller senses that there is no longer any torque force applied to the drag motor  286 , as is the case in the event of wire breakage, the controller stops the sheeter device  210  and the pull motor  288 . The pinch roller  296 ,  297  design insures that the feed spool  282  will never come unraveled regardless of the mode of operation or whether the sheeter wire  260  breaks. 
     In order to be compatible with use in the food industry which requires frequent antiseptic cleaning, it is recommended that as many as possible of the components disclosed be made of stainless steel. For example, the two posts  292 ,  294  can be simple stainless steel rods. A suitable motor for both the drag motor  280  and the pull motor  288  is the Bulletin 1326 Servo Motor manufactured by Allen Bradley. This motor is operated in the “torque mode” when used as a drag motor  286  and the “velocity mode” when used as a pull motor  288 . The use of a single motor compatible for use as either the drag motor  286  or pull motor  288  facilitates a smaller spare parts inventory. The sheeter wire  260  is again commercially available piano wire which is wrapped to a set tension on the feed spool  282  prior to installation for use with the invention. 
     This invention is an improvement over the prior art in that it is a simple, fail safe design improving upon the concept of a continuous sheeter wire apparatus. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.