Abstract:
A method and apparatus for chopping long unwound items like fiber, fiber strands, yarn, etc. having an idler roll for pressing the item(s) against a backup roll for pulling the item(s) into the chopper uses an improved mount for the idler roll that maintains the outer peripheral surface of the idler roll into more consistent contact with more consistent force with the item(s) being chopped.

Description:
BACKGROUND 
     The present invention involves an improved chopper for chopping continuous or very long loose items such as fiber, fiber strands, yarn, wire, string, ribbon, tape and the like by pulling the item(s) into the chopper while the loose items are held tightly against the surface of a rotating backup roll with a rotating idler roll biased against the backup roll and carrying the item(s) on into a nip between a rotating blade roll and the rotating backup roll where they are separated into short pieces. More specifically the present invention involves a chopper having an improved mounting for an idler roll which allows the idler roll to reliably self align with the surface of a back up roll to more reliably and more effectively hold down and pull item(s) being pulled and chopped such as loose wet or dry strands of glass fibers with, or without, a chemical sizing thereon. 
     It has long been known to chop continuous fibers or fiber strands into short lengths of about 3 inches or shorter. Billions of pounds of such product including chopped glass fibers and fiber strands are produced each year in process and chopping apparatus such as disclosed in U.S. Pat. Nos. 5,970,837, 4,398,934, 3,508,461, and 3,869,268, the disclosures of which are incorporated herein by reference. The choppers disclosed in these patents comprise a blade roll containing a plurality of spaced apart blades for separating the fibers into short lengths, a backup roll, usually driven, which the blades work against to effect the separation and which pulls the fibers or fiber strands and an idler roll to hold the fibers or fiber strands down onto the surface of the backup roll. In the chopped fiber processes disclosed in these patents, the chopper is usually the most productivity limiting equipment in the processes which are 365×24 type processes, i.e. operate continuously every day of the year, 24 hours each day. Therefore, improvements in the chopper which allow the chopper to pull and chop faster, for longer times between maintenance shutdowns, and/or to pull and chop more fibers or fiber strands at a time have an extremely positive impact on productivity and production costs. 
     In the published prior art the idler roll has been mounted and held against the surface of the back up roll in a generally rigid manner and with a variable force such as a force applied by an air or hydraulic cylinder. The working surface of the idler roll has been knurled and chrome plated in the past to better grip the fibers or fiber strands to prevent the fibers or fiber strands from sticking to the roll and wrapping and to avoid having to shut the chopper down to remove the wrap. Normally several strands such as up to 14 are fed into the chopper, each strand containing 2000 or more fibers. As more fiber strands and fibers are fed into the chopper it becomes more difficult to pull all of the strands and fibers at the same speed, so more pressure is applied to the cylinder pushing the idler roll against the backup roll with more force. If all of the strands or fibers are not pulled at the same speed, the slower strands and fibers will have a greater fiber diameter which is unacceptable and the bushings of the slower strands frequently will not operate at the proper temperature causing more frequent breakouts and/or additional fiber diameter variations, both of which are unacceptable. Also, fiber slippage can cause some of the fibers to be cut to shorter lengths than desired resulting in an unacceptable product. 
     As the pulling speed is increased, and/or as the number of strands and fibers are increased, above about 3000-4000 ft./min. (FPM), depending on the product, the present state of the art choppers begin to vibrate and the idler roll begins to allow one or more of the strands to slip some thus reducing the pulling speed of one or more of the strands. Also, if all of the strands are not pressed between the idler roll and the elastomer layer of the backup roll, a strand can slip partially out of the nip leaving some of the fibers unchopped, producing double cuts and stringers in the chopped product and causing the product to be scrapped. This condition worsens as the backup roll and blades become worn with use, typically about 6-24 hours following a chopper rebuild in which the blade roll is replaced with a roll having new blades and the backup roll is replaced with either a refurbished or new backup roll. The backup roll has a working layer of polyurethane at least about a half inch thick on the surface of a metal wheel. As the chopper life increases the surface of the backup roll becomes chopped up due to the blades pressing and cutting into the polyurethane. 
     Periodically the backup roll must be removed and either the polyurethane layer turned down on a lathe or sander or must be replaced with a new layer of polyurethane. It would be very desirable to be able to run the chopper at higher speed without vibration and strand slippage to make good chopped fiber than is possible with the current state of the art choppers because the remainder of the process is capable of producing fiber that can be pulled much faster in terms of speed and pounds of fiber per hour than is currently possible. Also, in the preferred state of the art chopper the idler roll mount is exposed to broken fiber and sizing being thrown from the various rolls on the chopper and must be frequently cleaned to avoid serious malfunction at current speeds. 
     SUMMARY OF THE INVENTION 
     It has been discovered that the reason for certain strands slipping on the idler/backup roll of the current choppers is the manner in which the idler roll is mounted, the manner in which the force is applied to hold the idler roll onto the surface of the backup roll and the fact that the peripheral surface of a new and used backup rolls often have a slight taper from side-to-side or misalignment with the idler roll, either initially or after the new backup roll has been in use for a few hours. 
     The present invention is a chopper having an improved idler roll mount assembly for a chopper for separating long lengths of one or more unwound items selected from a group consisting of fibers, fiber strands, wires, strings, tape(s), strip(s) and ribbon(s) into short lengths while one or more of, preferably a plurality of, the long lengths of material are pulled into the chopper in an unwound form at speeds exceeding 1,000 FPM, preferably at speeds exceeding 2000 FPM by a rotating idler roll pressing the item(s) against the peripheral surface of an elastomer layer on the peripheral surface of a rotating backup roll which carries the item(s) on into a nip between the elastomer layer and a rotating blade roll. The item(s) being chopped can be either dry or wet with or without a chemical sizing on the surface of the item(s). The chopper having an improved idler roll mount assembly comprises a blade roll having a plurality of spaced apart blades in its peripheral surface, a backup roll having an elastomeric working layer on its periphery, and an idler roll, preferably having a knurled surface. 
     The improvement comprises a mount assembly for the idler roll having a yoke spaced from the peripheral surface of the idler roll that spans the length of the idler roll and beyond, each end of which turns down to support an axle about which the idler roll is free to rotate, a connector connecting said yoke to a shaft whose axis is perpendicular to an axis of said connector, said connector allowing said yoke to rotate back and forth around the axis of said connector, said shaft being held in a rotatable manner by a structural member of the chopper in such a manner that the outer peripheral surface of the idler roll is or can be in contact with, preferably with the full width of, the outer peripheral surface of the backup roll and/or item(s) on the outer peripheral surface to be chopped, an arm rigidly connected to said shaft, a source of a variable force for said arm or a means for applying a variable force to said arm, which force causes the outer peripheral surface of said idler roll to press against either the peripheral surface of said backup roll or against one or more of said items laying on the peripheral surface of said backup roll and thus holding the peripheral surface of said idler roll into pulling contact with said one or more of said items. Preferably, the chopper has an enclosed cabinet on the inboard side of the outboard face of the front plate and preferably at least some of the components of the idler roll mount are located in this cabinet to protect them from foreign matter in the environment around the idler roll. This foreign matter includes water mist, chemical sizing from the surface of fibers, dust and pieces of the item(s) being chopped. 
     The connector can either be a female socket or a male stub rigidly or rotatably attached to the shaft or to the yoke and the male stub is attached to either the yoke or to the shaft in either a rigid or rotatable manner. The preferred means for applying a force to the arm is either an air or hydraulic cylinder, most preferably an air cylinder, but can be other sources of force such as a high torque motor mounted to the structure of said chopper, the rotor of said motor eccentrically attached to said arm. The arm could be dispensed with by attaching the end of the shaft opposite the end portion attached to the connector to a rotor of a high torque motor, the latter being mounted appropriately to a frame member of the chopper. 
     Optional items on the present invention include an air purge system for applying positive fluid pressure to the interior of the yoke pivoting mechanism, including the connector, to prevent foreign matter like water, chemical sizing and fiber or fiber chips from entering and impeding the free pivoting action. The fluid is preferably air but could be other gases and liquids such as water. Also, the air purge system can include a fluid cooling system for the idler roll bearing(s) as well as positive fluid pressure in the interior of the idler roll, again to prevent intrusion by foreign material present in the vicinity of the idler roll during operation and cleaning. Other optional features include means for limiting the degree of rotation of the idler roll yoke or axis as an aid to a mechanic when changing a backup roll and locator means to aid the mechanic, etc. in replacing an idler roll or idler roll mount sub-assembly. Also, various known means for applying a force to press the idler roll into the item(s) being chopped and towards the surface of the elastomer layer can be used. 
     The invention also includes a method of chopping items as described above using an improved chopper containing an improved idler roll mount as described above to permit a higher productivity of chopped fiber than is obtained with prior art choppers while also enjoying an idler roll mount that does not require frequent cleaning to avoid malfunctions and/or scrap caused by an exposed idler roll mount and force actuator. 
     When the word “about” is used herein it is meant that the amount or condition it modifies can vary some beyond that so long as the advantages of the invention are realized. Practically, there is rarely the time or resources available to very precisely determine the limits of all the parameters of one&#39;s invention because to do so would require an effort far greater than can be justified at the time the invention is being developed to a commercial reality. The skilled artisan understands this and expects that the disclosed results of the invention might extend, at least somewhat, beyond one or more of the limits disclosed. Later, having the benefit of the inventors disclosure and understanding the inventive concept and embodiments disclosed including the best mode known to the inventor, the inventor and others can, without inventive effort, explore beyond the limits disclosed to determine if the invention is realized beyond those limits and, when embodiments are found to be without unexpected characteristics, those embodiments are within the meaning of the term about as used herein. It is not difficult for the skilled artisan or others to determine whether such an embodiment is either as might be expected or, because of either a break in the continuity of results or one or more features that are significantly better than reported by the inventor, is surprising and thus an unobvious teaching leading to a further advance in the art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a chopper of the present invention with a portion cut away to show the novel idler roll mount assembly. 
     FIG. 2 is a plan view of the preferred idler roll mount assembly shown in FIG.  1 . 
     FIG. 3 is an end view of the preferred idler roll mount assembly shown in FIGS. 1 and 2. 
     FIG. 4 is a back view of the preferred idler roll mount assembly shown in FIG.  1 . 
     FIG. 5 is a blown-up partial front view of the chopper showing the novel idler roll mount assembly of the present invention. 
     FIG. 6 is a partial plan view showing another embodiment of the novel idler roll mount assembly of the present invention. 
     FIG. 7 is a partial plan view showing still another embodiment of the novel idler roll mount assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a chopper  2  for separating long items such as fibers, fiber strands, strings, wires, tape(s) or ribbon(s)  1  into short lengths  3 . Typically the short lengths are about 3 inches or less, but can be longer if the diameter of the blade roll  12  and the backup roll  4  are more than about one meter. For purposes of describing the invention an improved chopper  2  for separating long fiber strands, such as glass fiber strands, is illustrated. Such a chopper typically comprises a backup roll  4  having an elastomer layer  6  on its outer periphery and mounted on a rotating spindle  8  and held on with a large washer  9  and nut  10 , a blade roll  12  having blades  14  spaced apart around its outer periphery and mounted on a rotating spindle  16  in a similar manner as the backup roll  4 . The typical chopper also comprises a front plate  5 , which preferably is an element of a conventional chopper frame (not shown) and a rotating idler roll  20  having a knurled surface that is pressed against the fiber strands  1  and the elastomer layer  6  of the backup roll  4 . The idler roll  20  serves the purpose of pressing the fiber strands  1  against the rotating backup roll  4  which will help pull the fiber strands  1  at the desired speed into the chopper  2 . Typically a strand separator and guide roll  18  mounted on or off the chopper is used to separate the fiber strands  1  and to guide them to the desired location on the backup roll  4 . 
     The improved chopper  2  of the present invention comprises a novel and preferred idler roll mount assembly  22 . The front plate  5  is partially cut away in FIG. 1 to show the parts of the idler roll mount assembly  22  that are behind the front plate  5 . 
     The idler roll mount assembly  22  of the present invention is illustrated in FIGS. 1-5 and comprises a C shaped yoke  23  spaced from the outer peripheral surface and the ends of the idler roll  20  and attached to each end of an axle  24  for the idler roll  20 . The yoke  23  is rotatably attached to a socket connector  26  with a stub shaft  25 . The stub shaft  25  is preferably rigidly attached to the yoke  23 , preferably by passing through the yoke at a location in which a longitudinal axis of the shaft will align generally close to a peripheral center line of the surface of the elastomer layer  6  of the backup roll  4  and is fixedly attached to the yoke  23  by welding, pinning or other suitable means in a known manner. By generally close is meant being within about 1 inch, preferably within about 0.5 inch and most preferably within about 0 to 0.25 inch from each other. 
     The connector  26  preferably has a first portion  27  having a first cylindrical opening  28  to hold the stub shaft  25  in a rotatable manner, preferably also lined with a bushing  29 , preferably a lubricated bushing, that allows the stub shaft  25  to freely rotate in the first portion  27 . The stub shaft  25  is retained in the first portion  27  by any known means such as by a snap ring  30 , which allows rotation of stub shaft  25  but prevents significant axial direction movement. 
     The connector  26  has a second portion  31  which has a second cylindrical opening  32 , the axis of which is perpendicular to the axis of the first cylindrical opening  28 . The second portion  31  of the connector  26  is rigidly attached to the first portion  27  by any suitable means such as by the welds  33 . The second cylindrical opening  32  surrounds an outboard end portion  35  of a main shaft  34 . The outboard end of the main shaft  34  is spaced from the outer periphery of the stub shaft  25 . The second portion is fixedly and removably attached to the main shaft  34  by any suitable means such as with a handle  36  and a first removable pin  37 , such as a McMaster-Carr™ stainless steel positive locking quick release T-handle pin to allow the exposed idler roll parts to be quickly removed and replaced without opening the housing of the chopper  2 . 
     An inboard portion  38  of the main shaft  34  is preferably held generally horizontally in a rotatable manner by a housing  39  having a cylindrical opening  40  therethrough, an axis of which aligns with the axis of the second cylindrical opening  32  in the connector  26 . An outboard end of the housing  39  is preferably attached to the plate  5  of the chopper either directly or preferably to a removable plate  42 , which is attached to the plate  5 , preferably with bolts. The housing  39  is of a length to preferably allow the inboard portion  38  of the main shaft  34  to extend beyond an inboard end of the housing  39  at least about 0.5 inch to permit any means of applying a torque to the main shaft  34 , such as a first end  41  of a torque arm  43  to be fixedly attached to the inboard portion  38  of the main shaft  34  in any suitable manner, such as by a key  52  in a slot or keyway as shown in FIG. 4 and a tightening bolt  88  shown in FIGS. 2 and 4. A first bushing  53  and a second bushing  56 , preferably both being lubricated bushings, with a gap  57  therebetween surround the main shaft  34  in the cylindrical opening  40  of the housing  39  to ease the rotation of the main shaft  34 . 
     A fluid cylinder  44 , preferably an air cylinder, is located inside the chopper  2  housing on the inboard side of the plate  5  by any suitable means, such as with a cylinder mount  50 , with the cylinder rod  49  attached to a clevis  46  attached to a second end portion  45  of the torque arm  43  opposite the first end portion  41 . Air or other fluid is fed to the cylinder  44  via either one of a first line  47  or a second line  48  depending on whether the idler roll  20  is being pressed against the elastomer layer  6  or backed away from the elastomer roll  6 . A first fluid pressure regulator  51  is connected to line  47 , which is used to regulate the amount of force applied to the torque arm  43  which in turn regulates the force the idler roll  20  applies to the elastomer layer  6  and the item being chopped such as strands  1 . 
     Optionally, but preferably, the idler roll mount assembly  22  can also be equipped with an air purge system, shown in FIGS. 2 and 3, to prevent water, chemical sizing and fiber dust that are prevalent in the air surrounding the idler roll and mount from entering the bushings or bearings in the idler roll mount assembly  22  or idler roll  20  and reducing the freeness of rotation of the moving parts. The air purge system comprises a purge air line  54  connected to the end of the inboard portion  38  of the main shaft  34  where it aligns with a first channel  55  that runs through the interior of the main shaft  34  and empties into a cavity  59  at the end of the main shaft  34  and inside the openings in the connector  26 . This cavity  59  feeds purge air into a second channel  60  which communicates on one end with a space between the bushing  29  and the stub shaft  25  between two “O” rings  58  and with a third channel  61  on the other end whereby purge air flows through the third channel  61  into the interior of the yoke  23 . The third channel  61  preferably lies on an axis  72  of the stub shaft  25 . 
     The third channel  61  communicates with a fourth channel  62 , which is in the interior of the yoke  23  and extends to the idler roll axle  24 . 
     A limited amount of purge air can also optionally flow from the cavity  59  out between the stub shaft  25  and the bushing  29  through the first cylindrical opening  28  towards the snap ring  30  and even towards yoke  23  which prevents foreign material from entering this first cylindrical opening  28 . Foreign material entering the first cylindrical opening  28  would after a time impede the pivoting movement of the yoke  23  and idler roll  20  and cause non-uniformity in the pressing force exerted by the surface of the rotating idler roll  20  on the items being chopped and the backup roll  6 . 
     The fourth channel  62  empties into a fifth channel  63  (FIG. 3) running down a portion of the length of an axis of the idler roll axle  24 . The fifth channel  63  dumps purge air into a sixth channel  64  which preferably, but not necessarily, runs completely through idler roll axle  24  to dump purge air into a reservoir  65 . The reservoir  65  preferably, but not necessarily, surrounds a portion of the length of the idler roll axle  24  and communicates with idler roll bearings  68  located near both ends of the idler roll axle  24 . The fifth channel  63  also dumps purge air into seventh channel  66  and eighth channel  67  each located at opposite ends portions of the idler roll axle  24  outside of idler roll bearings  68 . Purge air escapes from the idler roll through escape spaces  69  at each end portions of the idler roll axle  24  outboard of the seventh and eighth channels  66 ,  67  to prevent foreign matter from entering the idler roll bearings  68  and various internal clearances which could impede rotation of the idler roll  20 . The proper air pressure to achieve these results while conserving high-pressure air is regulated with a second pressure regulator  80  in the second air line  54 . 
     While the preferred purge air system of the present invention has been shown, once given this concept, it will be obvious that many modifications can be made to this system to get the air, or other fluid such as water or other gas, to the desired locations to achieve the same or similar result. Other modifications to the idler roll mount assembly  22  will also be obvious given the disclosure above. 
     Another optional feature is shown in FIG. 2. A U shaped slot  82  can be formed in the end of the first portion  27  of the connector  26  opposite the yoke  23  and centered above the axis  72  of the stub shaft  25  with the open end of the U being on the edge and end of the connector  26  as shown. A second removable pin  83  is placed in a vertical hole in the stub shaft  25  after the idler roll  20 , yoke  23  and stub shaft  25  with snap ring  30  have been installed onto the connector  26 . The location of the second removable pin  83 , when in the hole in the stub shaft  25  and centered in the U shaped slot  82 , is such that when the second removable pin  83  is vertical, the axis of the idler roll  20  is horizontal. The width of the slot  82  is greater than the width of the second removable pin  83  which allows the axis of the idler roll  20  to move off of horizontal a few degrees in clockwise and counter clockwise directions, preferably plus or minus about 2 or 3 degrees, but greater movement can used if desired or necessary. 
     The second removable pin  83  and wider slot  82  allows the surface of the idler roll  20  to follow different tapers on the peripheral surface across the width of the elastomeric layer  6 , but prevents it from rotating up to 180 degrees or more when the backup roll  4  is removed for replacement. If the idler roll  20  were free to rotate without limit, the operator would have to make sure the idler roll  20  was properly oriented before installing the backup roll  4 , which takes time and could also be difficult or awkward for one person to accomplish. 
     Another optional feature is shown in FIG.  2 . An elongated U-shaped slot  84  can be formed in the top inboard end of the second portion  31  of the connector  26 , preferably centered above a cylindrical axis of the second portion  31 . A locator pin  85  protrudes from the top of the main shaft  34 , is aligned with the axis of the main shaft  34  and is spaced between the outboard end of the second portion  31  and the hole in the main shaft  34  for the first removable pin  37 . The location of the elongated slot  84  and its closed end is such that when the locator pin  85  is in the slot  84  and against the closed end of the elongated slot  84 , the first removable pin  37  can be inserted into the appropriate hole for it in the main shaft  34 . 
     When the knurled surface of the idler roll becomes worn it becomes necessary to replace the idler roll  20  with a new or rebuilt one. To do this quickly, the removable pin  37  is pulled out using its handle  36  and the sub-assembly of the connector  26 , and attached parts including the idler roll  20 , is removed and replaced with a new sub-assembly. This optional feature reduces the time that would otherwise be required to properly position the new connector  26  to allow insertion of the removable pin  37 . The open end of the elongated slot  84  can be wider than the closed end portion if desired to make it easier to start the elongated slot  84  around the locator pin  85 . 
     The means for providing rotation of the idler roll yoke  23  to allow the peripheral surface of the idler toll  20  to closely follow the changing surface of the elastomer layer  6  on the backup roll  4  can be varied. Two such variations and different embodiments are shown in FIGS. 6 and 7. FIG. 6 is a partial plan view of another embodiment of the present invention. In this embodiment the idler roll  20  and idler roll axle  24 , shown in FIG. 2, are unchanged from the preferred embodiment, but a different C shaped yoke  70  contains the yoke pivot means inside the yoke  70  itself. A cylindrical opening  71  passes partway through the portion of the yoke  70  that spans the idler roll  20 , preferably at a location that will align the axis  72  of the opening  71  with or close to the centerline of the elastomer layer  6 . By close to is meant within one inch, preferably within 0.5 inch and most preferably within 0.25 inch. A bearing or bushing  73  rests in the larger diameter portion of the opening  71  and on a ledge yoke  70  in the opening  71 . In this embodiment an L shaped connector  74 , of a type that can be connected to the main shaft  34  in the same or similar manner as connector  26 , has a round stub shaft  75  of smaller diameter than the connector  74  on the end opposite the end for connecting to the main shaft  34 . The stub shaft  75  passes through the bearing  73  and entirely through the yoke  70  with a snap ring  76 , or pin or other retainer, attached to the stub shaft  75  next to the surface of the yoke  70  closest to the surface of the idler roll  20  to hold the yoke  70  onto the connector  74  in a rotatable manner. A modification of this embodiment would use two spaced part bearings in place of the single bearing  73  to improve the structural rigidity. Plate  79 , bolted to the yoke  70  as shown retains the bearing  73  in the opening  71 . 
     The embodiment shown in FIG. 6 can optionally be equipped with the air purge concept described above. In such case a passage  77  communicates with a source of high pressure fluid like air in the main shaft  34  on one end and with a space between the opening  71  and the stub shaft  75  to dump air into this space so that the air can flow towards both ends of the opening  71  to keep foreign material out of the opening  71  and to provide an air cushion between the bearing  73  and the connector  77 . Additional yoke passages could also be provided to allow purge air to also flow to the idler roll axle  24  in a similar manner as shown in FIG.  2 . 
     FIG. 7 shows a still further embodiment in which the idler roll  20 , idler roll axle  24 , yoke  23 , stub shaft  25  and snap ring  30  are unchanged from the preferred embodiment shown in FIGS. 2-5. A simpler connector  78  is used. The connector attaches to the main shaft  34  in the same manner as the connector  26  in the preferred embodiment, but has only one portion and has a cylindrical opening  79  completely through the connector  78 , the axis of the opening being perpendicular to the axis of the main shaft  34 . If desired this embodiment can also be equipped with the same or similar air purge system of the preferred embodiment, as well as same or similar shaft bushings and locating pins and guide slots and pins. A still further embodiment places the point of rotation in the stub shaft itself at a point between where the stub shaft  25 , attaches to either the connector of FIG. 2 or the main shaft of FIG.  7  and the yoke  23 . Other alternative embodiments to achieve the same function of permitting the idler roll to follow the surface of the backup roll and the item(s) being chopped will be obvious to the chopper artisan. 
     In the preferred embodiment disclosed herein, many of the parts of the novel idler roll and mount assembly are contained within the chopper cabinet behind the front plate  5  to protect the parts from the hostile environment on the outside of the chopper. However, if one wanted to put up with the problems caused by the environment outside the chopper cabinet in front of the front plate  5  more or all of the novel idler roll mount assembly could be located outside the chopper cabinet. 
     It will be obvious to chopper artisans that the embodiments disclosed and the structures can be modified in several ways without significantly changing the result. For example, instead of an air purge system, a lubricating system using a lubricant compatible with the chopped fiber product can be used. Also, instead of a fluid cylinder  44 , various types of springs such as coil, leaf, torsion bar, flexible rods, etc. can be used in a well known manner to apply the force needed to bias the idler roll  20  against the items to be chopped  3  against the elastomer layer  6  of the backup roll  4 . All such modifications are within the concept and scope of the present invention described in the following claims.