Abstract:
The present invention provides a web perforating apparatus which includes a system for detecting and indicating when a blade in the apparatus is broken, dull or otherwise not perforating the web. The apparatus is typically used with rewinders or other similar machines that produce perforated sheets of products, such as paper, using sets of stationary anvil blades and rotating perforating blades. The apparatus comprises at least one anvil including a blade holder and an anvil blade which is positioned within the blade holder. The blade holder is formed of an insulating material for electrically isolating the anvil blade from the machine frame of the rewinder. An electrical conductor is coupled to the anvil blade for supplying an electric current to the anvil blade from a current source. The apparatus also includes at least one grounded perforating blade for moving relative to the anvil blade and cooperating with the anvil blade to perforate the web at predetermined points along its length. The perforating blade will contact the anvil blade after perforating the web. A closed circuit is formed and maintained along the anvil blade at points where the blades are in contact with each other. The apparatus further includes means for detecting if a closed circuit has been formed and maintained along the anvil blade when the perforating blade moves into a position where the blades should contact each other.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a system for detecting when a web is not being completely perforated, cut, scored or otherwise weakened at spaced intervals along its length, and more particularly to a web perforating system that detects and indicates when a perforator in a rewinder or similar machine is operating with a broken or dull perforating blade.  
           [0003]    2. Description of the Prior Art  
           [0004]    During the production of paper products such as toilet tissue and paper towel rolls, a paper web is unwound from a parent roll by a rewinder as is well known in the art. As the paper web enters the rewinder, it contacts one or more rolls which deliver it to a web cutting apparatus or “perforator” that is equipped with a perforating roll. One such perforator is disclosed in U.S. Pat. No. 2,870,840 to Kwitek which is hereby expressly and completely incorporated by reference. The perforator includes a perforating roll carrying rows of perforating blades or “fly knives.” These rows are spaced from each other along the circumference of the perforating roll. The perforating blades rotate relative to and cooperate with stationary anvils that carry anvil blades. The anvils are secured in a helical pattern to a perf anvil head which extends across the path of travel of the web. The perf anvil head in such a device can rotate relative to the perforating roll between an open position and an operating position. In an open position, the perf anvil head spaces the anvils from the perforating blades so that the web will not be perforated. When the perf anvil head is rotated into the operating position, the perforating blades contact the anvil blades and perforate the passing web, thereby creating perforations at predetermined spaced intervals in the passing web. After the web passes through the perforator, it moves to a winding system which winds it onto a core.  
           [0005]    A perforating roll can rotate at speeds typically up to 1500 feet per minute. As a result, the perforating blades experience high compressive and shearing forces when they contact the stationary anvil blades. These forces can cause a perforating blade to fail at any time during a production run. Additionally, over time, the teeth of a perforating blade can dull as a result of repeatedly impacting an anvil blade. When the perforator operates with a broken or dull blade, it may not fully perforate the web. As a result, rolls of paper products which are not fully perforated will be sent to the customer. Paper rolls with incomplete perforations are the largest complaint of perforated product customers.  
           [0006]    Perforating machines such as that discussed above lack a system for detecting if a perforating blade has broken or become so dull that it does not perforate the passing web. Instead, perforated paper producers rely on an operator to visually inspect the perforations between sheets of a wound paper product at regularly spaced time intervals, such as every hour. Between these inspections, a broken blade may only be detected if the operator hears a noise which suggests that a blade has broken. As difficult as it is for an operator to hear when the perforator is operating with a broken blade, it is virtually impossible to detect if it is operating with a dull blade without visually inspecting the perforated rolls.  
           [0007]    If a perforating blade breaks or becomes too dull to properly perforate the web at any time between visual inspections, the machine will continue to operate and produce incomplete perforated products until at least the next visual inspection. For example, if the operator stops and examines the results of the perforating process every hour, a blade that breaks fifteen minutes into a run will cause the perforator to produce forty-five minutes worth of improperly perforated sheet product. This can add up to a significant amount of improperly perforated product when the rewinder is operating at 1500 or more feet of paper web per minute. Additional problems associated with visual inspection are the loss of production time if the line is shut down while the visual inspection is performed, and the waste of the product that is used for the inspection.  
           [0008]    Various machines have included systems to detect when a web has not been properly prepared. One such system is disclosed in U.S. Pat. Nos. 4,813,320 and 5,091,962 to Malloy et al. which disclose a stamping machine having an associated sensing device for determining when a stamped web has been incorrectly fed. After the web is stamped, it passes from the press to a sensing device which includes an internal coil for generating an electromagnetic flux field. The sensing device produces a waveform which is based upon the amount of metal in the web and the position of the stamped portions relative to the sensors. This waveform is compared to a reference waveform. If a deviation exists between the waveforms, this indicates that the web was incorrectly fed. The stamping machine is then stopped and the position of the web is corrected. However, since the sensing device is spaced away from the press, the press will continue to stamp the incorrectly fed web and create waste for the length of time that it takes the frame with the first perceptible amount of deviation to reach the sensor.  
           [0009]    U.S. Pat. No. 3,339,434 to Sparling discloses a drill press including a monitoring apparatus that generates a control signal when the drill bit is broken or dull. The monitoring apparatus measures the duration of each drilling cycle and compares it with a reference cycle. Extended cycle times are caused by broken or dull drill bits taking longer to contact a reference point, such as the work piece, than a normally operating drill bit. When the measured cycle exceeds the reference cycle, a control signal is generated, indicating that a problem exists with the process. An apparatus which uses a timing cycle for monitoring a plurality of drill bits is also disclosed.  
           [0010]    U.S. Pat. No. 2,792,833 to Pokorski discloses an automated cutting press that forces a cutting die through a sheet material until it contacts a cutting block. The reciprocating die and cutting block include electrically conductive surfaces. A detection system establishes a circuit when the die and cutting block contact each other. The circuit affects the retraction of the die to its starting position so that the cycle can be repeated. This system is designed to automate the operation of the press, not to detect the presence of a broken tool. Additionally, this system will operate with a broken tool, as long as the tool can be forced through the sheet material and at some time contact the cutting block. This can result in a substrate cut that is not properly sized or shaped.  
           [0011]    It is an object of the present invention to overcome the drawbacks associated with the prior art rewinders and perforators.  
           [0012]    It is also an object of the present invention to provide a perforator that detects and indicates when one of its blades breaks or becomes so dull that it cannot properly perforate a web.  
           [0013]    A further object of the invention is to provide a method for detecting when a perforator is operating with a broken or dull perforating blade.  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention provides a web perforating apparatus which includes a system for detecting and indicating when a blade in the apparatus is broken, dull or otherwise not making contact with an opposing blade and thereby not perforating the web. This apparatus is typically used with rewinders or other similar machines that produce perforated sheets of products, such as paper, using sets of stationary anvil blades and rotating perforating blades. The perforating blades are typically attached to a bed roll and rotate relative to the anvil blades. These anvil and perforating blades are finely adjusted to make light, accurate contact with each other. As the perforating blades contact the web extending across the anvil blades, perforated product is produced. The anvil blades are solid in profile shape and connected to a movable mounting bar by blade holders. The blade holders secured to the rewinder also hold electric conductors for supplying a low amperage current to the anvil blades. The anvil blades and conductors are insulated from the grounded blade holders and the remainder of the machine base so the applied current does not go to ground.  
           [0015]    The electric current is used to detect when the perforating blade is not extending through the web and contacting the anvil blade. As the grounded perforating blades make contact with the current carrying anvil blades, a closed circuit is formed, a signal is generated and a representation, such as a waveform is produced. When all the perforating blades properly contact the anvil blades, a “normal” waveform is produced and recorded. If a perforating blade is broken, the recorded waveform will include an anomaly. The presence of the anomaly can be transmitted to the machine operator via a flashing light, siren etc. When an anomaly is detected, the machine can be quickly, if not immediately or automatically, shut down and the broken blade changed so as to reduce the amount of unperforated product. This detection system prevents a broken blade from unknowingly being used during the production of perforated paper product.  
           [0016]    In an embodiment of the present invention, the apparatus comprises at least one anvil including a blade holder and an anvil blade which is positioned within the blade holder. The blade holder is formed of an insulating material for electrically isolating the anvil blade from the machine frame of the rewinder. An electrical conductor is coupled to the anvil blade for supplying an electric current to the anvil blade from a current source. The apparatus also includes at least one grounded perforating blade for moving relative to the at least one anvil blade and cooperating with the at least one anvil blade to perforate the web at predetermined points along its length. The at least one perforating blade will contact the anvil blade after perforating the web. A closed circuit is formed and maintained along the at least one anvil blade as long as the perforating blade remains in contact with the anvil blade. Since the anvil blades are on a spiral mount, their contact with the perforation blades is progressive. This results in progressive single point contact between the perporation and anvil blades along the length of the anvil blades. The apparatus further includes means for detecting if a closed circuit has been formed and maintained along the anvil blade when the perforating blade moves into a position where it should make contact with the anvil blade.  
           [0017]    The present invention also includes a method for perforating a web using a perforating apparatus and detecting when the web is not being completely perforated. The method comprises the steps of grounding a first blade of the perforating apparatus, electrically isolating a second blade of the perforating apparatus from a ground and connecting the isolated second blade to an electric current source. The method also includes moving one of the blades relative to the other blade so at least a portion of the first blade contacts a portion of the second blade, and creating a closed circuit at points along the second blade where contact is made between the second blade and the first blade. A step of generating a signal which represents where closed circuits were created along the second blade also forms part of the present invention. Additionally, the method can include the steps of comparing the generated signal to a reference signal, and indicating to an attendant when the generated signal differs from the reference signal.  
           [0018]    According to the present invention, an operator will be notified and the perforation run stopped as soon as a broken or dull blade is detected, thereby keeping the amount of unperforated product to a minimum. This will significantly reduce waste and down time by doing away with the need to shut down the run to visually inspect the blades and the need to unroll the produced product to visually inspect the perforations or lack thereof. Moreover, rolls of completely perforated paper can be critical to the operation of dispensers which use the perforation rows to recognize the leading edge of a sheet in order to either begin or stop the paper dispensing process. Proper perforation rows also facilitate clean and complete separation of the sheet when pulled by user. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0019]    [0019]FIG. 1 is a perspective view showing the web perforating apparatus according to the present invention with a perf anvil head partially illustrated;  
         [0020]    [0020]FIG. 2 is a diagrammatic view of a perforation detecting and indicating system according to the present invention;  
         [0021]    [0021]FIG. 3 is a cross section of an anvil shown in FIG. 1;  
         [0022]    [0022]FIG. 4 is a cross section of the perforating apparatus with a perforating roll shown in partial cross section and an anvil shown in cross section;  
         [0023]    [0023]FIG. 5 is an exploded end view of an anvil shown in FIG. 1 and electric current delivering members;  
         [0024]    [0024]FIG. 6 is a sectional view looking down a perforating shaft showing an anvil blade and a perforating blade in a perforating or cutting step;  
         [0025]    [0025]FIG. 7 is an exploded perspective view of an anvil as shown in FIG. 5 and electric current delivering members;  
         [0026]    [0026]FIG. 8 illustrates a representative waveform or trace indicating that a closed circuit was formed and maintained along the lengths of monitored anvil blades A and B;  
         [0027]    [0027]FIG. 9 illustrates a representative waveform or trace indicating that open and closed circuits were formed along the lengths of the monitored anvil blades A and B;  
         [0028]    [0028]FIG. 10 illustrates a perforating blade according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    [0029]FIG. 1 illustrates an apparatus  10  including a perforator  15  which is used with a rewinder or similar converting machine for forming lines of perforations, scoring or otherwise weakening a web  12 . The lines of perforations are formed at regular or differing intervals along the length of the web  12  and extend across the web  12  in a direction normal to its length. The web  12  can be of any material that is capable of being perforated, especially, materials such as paper or a plastic film that can be wound onto a core with each successive piece being able to be torn off for use. The apparatus  10  can be used with webs having one or more plies.  
         [0030]    The apparatus  10  is typically employed with a rewinder or related machinery. As well known in the art, the web  12  passes over a series of rollers which deliver it from the parent roll to the perforator  15  that is equipped with a perforating roll  20  that cooperates with a plurality of anvils  40  to perforate the web  12 . The perforating roll  20  includes an elongated tubular body  60  that can be from 70 to 100 inches long and have a substantially circular cross section, as illustrated in FIG. 6. However, other sized perforations rolls can also be used. The ends of the perforating roll  20  are positioned within bearings and secured to a gear that is driven by a series of gears connected to the output of a drive motor, as is known in the art. The bearings are also secured to the housing of the rewinder to prevent the perforating roll  20  from translating along the rewinder. Alternative known ways of driving the perforating roll  20  are also contemplated. The perforating roll  20  can operate at speeds of up to and exceeding 1000 revolutions per minute.  
         [0031]    As shown in FIG. 1, the perforating roll  20  includes transverse rows of perforating blades  21  which are each received in a transversely extending blade holding recess  22 . The recesses  22  extend along the length of the perforating roll in a direction substantially parallel to the longitudinal axis of the bed roll  20 . Each blade receiving recess  22  has a bearing surface  23  and a notch  24  underlying the installed perforating blade  21 , as shown in FIG. 4. The notch  24  relieves the forward edge of the perforating blade  21  during flexing. The transversely extending recesses  20  are spaced from each other around the circumference of the perforating roll  20  by a distance which corresponds to the desired interval between the lines of perforations in the web  12 . The shorter the interval between perforations, the more recesses  22  and rows of perforating blades  21  on the perforating roll  20 . In a preferred embodiment, the perforating roll  20  includes four longitudinally extending rows of perforating blades  21 . However, between three and six rows can also be spaced around the perforating roll  20 .  
         [0032]    A blade clamp  26  secures each perforating blade to the perforating roll  20  within its respective recess  22 . Each blade clamp  26  includes a clamping shoe  28  and an interference bolt  27  which is threaded into a tapped hole in the perforating roll  20 . A piece of resilient material  29 , such as rubber, can be positioned between the blade  21  and the perforating roll  60 . In a preferred embodiment, the perforating blades  21  are secured to the perforating roll  20  so that their forward ends extend a small distance away, such as 0.060 inches from the periphery of the perforating roll  20 .  
         [0033]    Each perforating blade  21  is typically between four and six inches long. The number of perforating blades  21  within a recess  22  depends on the width of the web being perforated. The wider the web  12 , the more perforating blades  21  that must be secured within the recesses  22  of the perforating roll  20 . The perforating blades  21  are formed of a resilient steel which flexes when making contact with the anvils  40  during the operation of the perforator. In a preferred embodiment, each perforating blade  21  has a thickness of approximately 0.032 inches which allows it to deflect slightly when it contacts an anvil  40 , as discussed below. However, any well known perforating blade could be used with the present invention. Each perforating blade  21  includes a cutting edge  75  having a length aligned with the length of the perforating roll. The cutting edge includes a plurality of cutting contact members  76  that are separated by recesses  77  to create an interrupted cutting surface. This interrupted surface creates the perforated cut extending across the width of the web  12 .  
         [0034]    As shown in FIG. 1, the perforator includes a pivotable perf anvil head  80  carrying the anvils  40 . The anvils  40  extend in a substantially helical pattern across the perf head  80  in a direction which is transverse to the path of travel of the web, as seen in FIG. 1. Each anvil  40  is securely fastened to the perf head  80  to prevent their relative movement during the operation of the perforator. One side of the perf head  80  is rotatably secured to a shaft (not shown) that is connected to the housing of the rewinder or similar machine. The other side of the perf head  80  is connected to a lifting mechanism (not shown) such as a pneumatic cylinder for moving the perf head  80  up to an “open” position and down to an “operating” position. When the lifting mechanism is activated and the perf head  80  is in an operating position, the anvils  40  are positioned to contact their respective perforating blades  21  and perforate the web  12 . When the perf head  80  is in an open position, the anvils  40  are spaced away from the perforating blades  21  so that perforation of the web  12  does not occur and the web  12  passes cleanly over the perforating blades  21 .  
         [0035]    As shown in FIGS. 5 and 7, each anvil  40  has an anvil block  43  which includes a channel  41  with a U-shaped cross section. An anvil blade holder  42  and a respective metal anvil blade  45  are secured within the channel  41 . The channel  41  is tilted within the anvil  40  so that its bottom wall extends at an angle to the upper surface  48  of the anvil  40  to maintain the proper angle of contact between the anvil blades  45  and the perforating blades  21 . Each anvil block  43  is typically formed of a rigid material such a steel that will not fail during the operation of the perforator. Two spring urged bolts (not shown) extend through each anvil block  43  for securing it to the perf head  80 . The anvil blocks  43  are also connected to the perf head  80  by a central threaded bolt  81  which is received in a threaded hole in the anvil  40 . In addition, a pair of adjustment screws  82  are positioned on either side of this central bolt  81  for adjusting the distance the anvil  40  is from the perforating roll  20  in order to control the pressure that an anvil blade  45  makes with a respective set of perforating blades  21 , as is well known. For example, if one end of the anvil blade  45  needs to make additional contact with the perforating blades  21  to achieve a complete perforation of the web  12 , the adjustment bolt  82  on that side of the anvil block  43  is advanced against the bottom of the anvil block  43 , in order to move the anvil blade  45  into contact with the perforating blades  21 . The anvil blade holder  42  is formed of DELRIN or other well known electrically insulating materials that will not fracture during the operation of the perforator.  
         [0036]    A shoe  55  and an interference screws  56  secure blade holder  42  within channel  41 . As shown in FIG. 3, the blade holder  42  includes a groove  44  for receiving the metal anvil blade  45  and electrically isolating it from its respective anvil block  43  and the other metal parts of the anvil  40 . The shoe  55  is positioned within channel  41  between one of its inner walls and a cantilevered portion  47  of the blade holder  42 . As the interference screws  56  are advanced through a tapped hole  46  in the anvil block  43 , the shoe  55  is advanced toward the anvil blade  45  and deflects the cantilevered portion  47  in the direction of the anvil blade  45  for securing the anvil blade  45  within the groove  44 .  
         [0037]    In order to accommodate the insulating blade holders  42 , the anvil blocks  43  according to the present invention extend further away from the mounting surface  84  of perf head  80  than do conventional anvil blocks. As a result, the anvil blades  45  are also positioned further away from the mounting surface  84  on the perf head  80  than conventional anvil blades. To compensate for this change in distance and to allow the present invention to be used with conventional perforators, the groove  44  positions the anvil blade  45  at a different angle than conventional anvils. This results in the contact angle between the perforating blades  21  and the anvil blades  45  being the same, or substantially the same, as that accomplished by the apparatus shown in U.S. Pat. No. 2,870,840 to Kwitek. The difference between the angle at which groove  44  positions the anvil blade  45  and the conventional positioning angle will change from perforator to perforator depending on the size difference between a conventional anvil block and the anvil block according to the present invention. This angle also directs the forces applied to the anvil blade  45  by the perforating blade  21  into the anvil block  43 .  
         [0038]    As shown in FIGS. 3 and 4, the anvil blade  45  has a blade contacting face  49  extending at an angle to the upper surface of the anvil and the rotating perforating blades  21  when positioned in the blade receiving groove  44 . This contacting face  49  creates a contact area which permits the contacting members  76  of the perforating blades  21  to strike the web  12  and the contacting face  49  of the anvil blade  45 , and perforate the web  12 , as shown in FIG. 6. The anvil blades  45  include a rigid steel bar or other such material with a thickness that will withstand the pressure applied by the perforating blades  21  without breaking.  
         [0039]    The anvils  40 , as shown best in FIG. 6, support the anvil blades  45  in a spiral arrangement along perf head  80 , as shown in FIG. 1, so that as each blade  21  of the perforating roll  20  moves in a counterclockwise direction, each of the contacting members  76  in longitudinal alignment on roll  20  engages a corresponding anvil blade  45  in a successive movement during the arc of travel shown between the first anvil  40  at the right of FIG. 6 and the last anvil  40  indicated at the left-hand side of FIG. 6. The distance between the first and last anvils  40  in the direction of the spiral arrangement is less than the distance between adjacent rows of the perforating blades  21  so that the signal, discussed below, generated for a first row of anvil blades  21  does not overlap with the signal for an adjacent row of anvil blades  21 . Not only is the row of blades  45 , as shown in FIG. 1, at an angle, but each individual blade  45  is at an angle so that the cutting at any instant is at a single point of contact.  
         [0040]    In the operation of the apparatus, the paper web  12  is advanced, as indicated by the arrows in FIG. 4, over the perforating roll  20 . As the web  12  is carried forwardly in the direction of the arrow on roll  20 , the blade  21  at one end of the roll  20  engages the anvil blade  45 , and then successively the blades  21  running longitudinally of roll  20 , engage the spirally-arranged individual anvil blades  45 , so as to perforate the web  12  transversely, the perforations, however, being produced sequentially from one edge of the web to the other. The perforated web  12  then leaves the roll  20  and is further processed.  
         [0041]    As previously discussed, the web  12  may not be fully perforated during the operation of the perforator  15  if one or more of the blades  21 ,  45  do not penetrate completely through the web  12  because they are broken or dull, or if one or both ends of an anvil blade  45  are not in proper position relative to the perforating roll  20 . The present invention includes a system for detecting and signaling an operator when one or more of the contacting members  76  of a perforating blade  21  do not fully cut through the passing web  12 . The detecting and signaling system supplies an electric current to the anvil blades  45  isolated by the insulating blade holder  42  when they are contacted by one of the grounded perforating blades  21 . Therefore, as the grounded contacting members  76  of the perforating blades  21  contact their respective anvil blades  45 , current flows to the contacted portion of the anvil blade  45  and a closed circuit is formed. This closed circuit can be electronically represented as a waveform and interpreted by the operator using a device such as an oscilloscope. Alternatively, the generated waveform representation can be received and compared to a reference waveform or other representation by a microprocessor. A logics program can also be used to provide a signal to the operator identifying the status of the perforation operation. If a closed circuit is created and maintained across the face of the anvil blade  45 , the generated electronic representation will be “normal” and the operator will know that the web  12  is being fully perforated. The generated representation can be a waveform or trace, as shown in FIG. 8, with a first vertical line  96  indicating when the closed circuit was created, a flat horizontal line  97  indicating that the circuit was maintained and a second vertical line  98  indicating when the circuit was opened.  
         [0042]    If for some reason, such as a broken, dull or out of position blade  21 ,  45 , a contacting member  76  does not pass through web  12  and contact the anvil blade  45 , an open circuit will exist at that position along the face of the anvil blade  45 . This open circuit is represented as an anomaly  95  or other type of deviation in the interpreted electronic representation. In one embodiment, when the representation of the formed circuit includes such an anomaly, the presence of the anomaly is visually evident in the generated waveform or trace displayed by an oscilloscope. Such a representation is shown in FIG. 9. As discussed above with respect to FIG. 8, the vertical lines  96 - 99  indicate when a closed circuit has been established and how long it is maintained along the length of the blade  45 . The presence of the anomaly can also be communicated to the operator by an audio or visual alarm, such as sirens or lights, produced by the logic carrying processor that interprets the generated circuit representation. The operator is then on notice that the perforator must be stopped and the blades  21 ,  45  inspected.  
         [0043]    In order to provide the electric current to the anvil blades  45 , the present invention includes an electric generator which produces a low amperage current at low voltage and low impedance. Electrically conductive probes  60  (also referred to as conductors) each contact a respective one of the anvil blades  45  and electrically couple the blades  45  to an electric current carrying cable  70  as shown in FIGS. 3 and 4. Each electrically conductive probe  60  is threaded into a tapped hole in one of the insulating blade holders  42 . A female end  65  of the probe  60  receives a male end  71  of the current carrying cable  70  for delivering the current carried by the cable  70  to the male end  64  of the probe  60  which contacts the anvil blade  45 . The male end  64  can be spring loaded so that it can move within the blade holder  42  in order to adjust to different sized cables and different sized anvil blades. When assembled, the current carrying male end  71  is electrically connected to the male end  64  of the probe  60  so that current will flow from the generator to the electrically isolated anvil blade  45 . The cable  70  includes a coupling cover  73  which mates with the outer surface of female end  65  to hold the cable  70  on the probe  60 . In a preferred embodiment, cables  70  are shielded similar to sparkplug wires. The shielded cables  70  prevent interference with the circuit and are easy to connect to the probes  60  on the anvil blade.  
         [0044]    During operation of the perforating apparatus  10 , a current having low amperage in the range of 100 milliamps is applied to the anvil blades  45  via cable  70  and probe  60 . The perforating roll  20  is rotated by a driving mechanism and perforating blades  21  move relative to the anvils  40 . Each perforating blade  21  contacts the web  12  extending between it and a respective one of the anvil blades  45 . However, before a perforating blade  21  contacts a cooperating anvil blade  45 , an open circuit exists across the anvil blade  45 . This open circuit is represented to the detecting system. As discussed above, the insulating blade holder  42  prevents the current applied to the anvil blade  45  from traveling to the anvil  40  or machine frame and thereby completing a circuit separate from the perforating blades  21 . As a contacting member  76  of the grounded perforating blade  21  makes contact with the anvil blade  45 , it acts like a switch and creates a closed (hot) circuit with the anvil blade  45  at each point of contact. This closed circuit will remain along the anvil blade  45  as long as one of the contacting members  76  of blade  21  is always in contact with blade  45 . When contact is interrupted as a result of a broken or dull perforating blade, or an out of position anvil blade, the circuit will open.  
         [0045]    The results of the contact between the perforating blades  21  and anvil blades  45  and the resulting circuit can be represented and monitored in many ways. One such way is to generate a signal that can be represented as a waveform, as discussed above and shown in FIGS. 8 and 9. In one embodiment, the generated signal is supplied to an oscilloscope which is monitored by an operator. As long as the generated trace is free of anomalies  95 , as shown in FIG. 8, the operator will permit the perforator to continue to operate normally. When a waveform having an anomaly, such as that shown in FIG. 9, is produced, the operator will stop the machine and change the broken blade  21 ,  45  or adjust the position of the anvil blade  45  relative to the perforating roll  20 . These anomalies are clearly visible on the oscilloscope. As a result, an experienced operator may be able to locate the broken portion of blade by merely looking at the location of the anomaly along the waveform.  
         [0046]    In another embodiment, the generated signal can be sent to a computer  90  and interpreted by a microprocessor  91 . In this embodiment, the microprocessor  91  compares the generated signal or waveform to a “normal”, reference waveform. When the generated waveform is the same as the reference waveform, the machine operates as normal. When the presence of an anomaly  95  is detected in the generated waveform, a logic circuit activates an alarm  92  which generates a signal alerting the operator to the existence of the anomaly and the fact that the web  12  is not being fully perforated. This signal can take the form of an audible message such as a statement or a siren. Alternatively, the signal could activate a flashing light or other visual indicators. It is contemplated that the machine can be automatically stopped when an anomaly is detected so that the minimum possible amount of unperforated product is produced.  
         [0047]    If the microprocessor  91  is used to detect the anomaly, it can also be used to indicate which contacting member(s)  76  is (are) not making contact with the anvil blades  45 . In this embodiment, a shaft encoder would be used in combination with the microprocessor  91  so that the microprocessor  91  will indicate the existence of the anomaly and its position along the length of the perforating shaft  20  and around its circumference. The shaft encoder is mounted on the machine frame and set so that the beginning of a row of perforating blades is at 0 degree. The contact with an anvil blade  45  of each successive perforating blade  21  will be interpreted as a different position along the 360 degree circumference of the shaft  20  as a result of the helical positioning of the anvil blades  45 . Therefore, as the shaft  20  rotates and the perforating blades  21  pass the helically positioned anvil blades  45 , the contact point being analyzed will move along the circumference of the perforating shaft  20 . For example, if the last anvil blade  45  is  30  degrees offset along the circumference of the perforating shaft  20  from the first anvil blade  45 , an anomaly detected at 30 degrees will be in the last blade  21  of the first row. If there are four rows of perforating blades, then an anomaly detected at 105 degrees will be in the center perforating blade  21  in the second row.  
         [0048]    Numerous characteristics, advantages and embodiments of the invention have been described in detail in the foregoing description with reference to the accompanying drawings. However, the disclosure is illustrative only and the invention is not limited to the illustrated embodiments. Various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention. For example, the current could be provided to the rotating perforating blades  21  by positioning electrical brushes in contact with the shaft  20  and the anvil blades  45  could be grounded. Also, the web can be fed into the perforator and across the face of the anvil blades as flat continuously moving substrate or it can be fed over the perforating roll so that it advances as the perforating roll rotates. Moreover, while disclosed to be used with systems that perforate a web in a direction normal to its length, the detecting system can be used with systems that perforate a web in directions parallel to its length.