WO2012036727A2

WO2012036727A2 - Adjustable tensioning device for fiber roving chopper

Info

Publication number: WO2012036727A2
Application number: PCT/US2011/001572
Authority: WO
Inventors: Jonathan R. Mcmichael; Corey D. Johnson
Original assignee: Graco Minnesota Inc.
Priority date: 2010-09-13
Filing date: 2011-09-13
Publication date: 2012-03-22
Also published as: TW201219179A; WO2012036727A3

Abstract

A tensioning device comprises a mounting plate, a slide bar, a hard stop, a soft stop, a locking device, a shaft and a chopper head. The mounting plate comprises a planar surface, and an slot having a slide surface disposed in the planar surface. The slide bar is disposed within the slot between first and second ends of the slide surface, and is linearly displaceable along the slide surface. The adjustable hard stop is disposed at the first end of the slot to limit linear displacement of the slide bar. The fixed soft stop is disposed at the second end of the slot to bias the slide bar toward the adjustable hard stop. The locking device immobilizes the slide bar within the slot. The shaft extends from the slide bar and the chopper head is coupled to the shaft.

Description

ADJUSTABLE TENSIONING DEVICE FOR FIBER ROVING CHOPPER

BACKGROUND

The present invention relates generally to a chopper device that distributes fiber material into a stream of resin material dispensed from a spray gun. In particular, the present invention relates to a device for controlling tension between a rotating cutter blade head and a rotating anvil.

Chopper guns are frequently used in the composite material industry to form large, shaped products, such as in the marine and watercraft industries and pool and spa industries. Chopper guns comprise assemblies of a fiber chopper and a liquid spray gun. Compressed air is typically supplied to power a pumping mechanism in the spray gun and an air motor in the fiber chopper. The spray gun typically receives a liquid resin material and a liquid catalyst material. Actuation of a trigger on the gun dispenses the materials into a mix chamber before being sprayed out of a nozzle of the gun. Mixing of the catalyst with the resin begins a solidification process, which eventually leads to a hard, rigid material being formed upon complete curing of the materials. The fiber chopper is typically mounted on top of the spray gun. The fiber chopper receives rovings of a fiber material, such as fiberglass, which passes between an idler wheel, an anvil and a cutter blade head. The fiber rovings are cut into small segments between the anvil and cutter blade head while being propelled out of the chopper by rotation of the anvil and the cutter blade head by the air motor. The segments of fiber are mixed into the sprayed mixture of resin and catalyst such that the final cured product is fiber reinforced.

The cutter blade head and anvil of the fiber chopper include consumable pieces that must be replaced after a threshold wear level is surpassed. For example, the cutter blade head typically includes a plurality of razor blades, and the anvil includes a roller of soft material into which the razor blades penetrate while slicing or chopping the fiber roving. However, even before the razor blades and roller need to be replaced, performance of the fiber chopper can be affected by wear of the consumable pieces. In particular, the razor blades can become dull and as a result do not completely cut the fiber rovings. The razor blades also degrade the anvil roller by effectively reducing the diameter of the anvil, which also results in incomplete cuts.

Degraded performance of the fiber chopper can be temporarily improved without having to replace the razor blades or anvil roller by repositioning the anvil closer to the cutter blade head. Prior art designs typically require that the chopper gun be disassembled to perform such adjustments. The inconvenience of such an operation often results in adjustments being disregarded in practice. Other externally activated devices, such as those described in U.S. Pat. No. 4,001 ,935 to Krohn et al. and U.S. Pat. No. 3, 155,320 to Jones, required the operator to precisely adjust tension between the cutter blade head and the anvil. If improperly adjusted, these mechanisms can result in incomplete cuts or rapidly worn razor blades. Other automatically adjusting tensioning devices require elaborate and complicated mechanisms that are prone to malfunction, such as that described in U.S. Pat. No. 3,491 ,443 to Fram. There is, therefore, a need for a simple, externally actuated system for automatically adjusting tension between a cutter blade head and an anvil in a fiber roving chopper.

SUMMARY

The present invention is directed to a tensioning device for adjusting position between rotatably engagable chopper heads in a fiber roving chopper. The tensioning device comprises a mounting plate, a slide bar, an adjustable hard stop, a fixed soft stop, a locking device, a first shaft and a first chopper head. The mounting plate comprises a planar surface against which heads are configured to rotate, and an slot disposed in the planar surface and having a slide surface extending from a first end to a second end. The slide bar is disposed within the slot between the first and second ends, and is linearly displaceable along the slide surface. The adjustable hard stop is disposed at the first end of the slot to limit linear displacement of the slide bar. The fixed soft stop is disposed at the second end of the slot to bias the slide bar toward the adjustable hard stop. The locking device immobilizes the slide bar within the slot. The first shaft extends from the slide bar. The first chopper head is coupled to the first shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a liquid spray gun and a fiber roving chopper assembly in which an adjustable tensioning device of the present invention is used.

FIG. 2A is a perspective view of the fiber roving chopper of FIG. 1 showing a fixed soft stop and a locking mechanism of the adjustable tensioning device.

FIG. 2B is a rear end view of the fiber roving chopper of FIG. 1 showing the locking mechanism and an adjustable hard stop of the adjustable tensioning device.

FIG. 3A is a perspective view of the fiber roving chopper of FIG. 1 with a cover removed to show a cutter blade head, an anvil head and an idler wheel.

FIG. 3B is a perspective view of the fiber roving chopper of FIG. 3A with the anvil head and idler wheel removed to show a slide bar of the adjustable tensioning device. FIG. 4 is a side cross-sectional view of the adjustable tensioning device taken at section 4-4 of FIG. 3B showing shafts for attachment of the anvil head and idler wheel to the slide bar of the adjustable tensioning device.

FIG. 5 is an end cross-sectional view of the adjustable tensioning device taken at section 5-5 of FIG. 3B showing an overhang feature for retaining the slide bar within a slide slot.

DETAILED DESCRIPTION

FIG. 1 is an exploded view of an assembly of liquid spray gun 10 and fiber roving chopper 12 in which an adjustable tensioning device of the present invention may be used. In FIG. 1 , fiber roving chopper 12 is shown slightly enlarged with respect to liquid spray gun 10. Liquid spray gun 1 0 comprises a two component internal mixing gun having handle 14, valve body 16, nozzle 18 and trigger 20. Fiber roving chopper 12 includes air motor 22, housing 24 and cover 26. Valve body 16 of spray gun 10 includes valve assembly 28, air inlet 30, material inlet 32, catalyst inlet 34 and air outlet 36. Housing 24 of fiber roving chopper 12 includes fiber inlets 38, locking mechanism 40, adjustable hard stop 41 , fasteners 43A and 43B, knob 45; and cover 26 includes dispenser chute 42.

In the embodiment shown, spray gun 10 comprises a two component mixing gun that receives two liquid components that mix when dispensed to produce a mixture that cures into a hardened material. A first component comprises a resin material, such as a polyester resin or a vinyl ester, and is fed into valve body 16 at material inlet 32. A second component comprises a catalyst material that causes the resin material to harden, such as Methyl Ethyl Ketone Peroxide (MEKP), and is fed into valve body 16 at catalyst inlet 34. Material inlet 32 and catalyst inlet 34 feed materials, respectively, into valves seated within valve body 16 and connected to valve assembly 28. Other inlets are provided to gun 1 0 for other fluids such as a solvent. Actuation of trigger 20 simultaneously causes valves of valve assembly 28 to open and causes pressurized components to flow into nozzle 1 8. As shown, spray gun 10 comprises an internal mixer where the two components are pressurized at inlets 32 and 34 by an external source (not shown) and mixed within tube 44 before entering nozzle 1 8. Pressurized air may also be provided to nozzle 1 8 to shape or direct the mixed flow stream. In other embodiments, the materials are mixed outside of gun 1 0 after being pressurized within valve body 1 6 from an external source (such as a pump) with air from inlet 31 and atomized by a mixing nozzle.

Pressurized air from air inlet 30 is fed through valve body 16 to outlet 36, which connects to an inlet (not shown) on air motor 22 of fiber chopper 1 2. Rovings or strands of a fiber material, such as fiberglass, are fed into cover 26 through fiber inlets 38. Activation of air motor 22 by actuation of trigger 20 causes the rovings to be pulled into a cutter blade head by an anvil head engaged with an idler wheel mounted on housing 24, as will be discussed in greater detail with respect to FIGS. 3A and 3B. Positions of the anvil head and idler wheel are adjusted with respect to the cutter blade head using locking mechanism 40 and adjustable hard stop 41 of adjustable tensioning device 52. The chopped roving pieces are expelled from dispenser chute 42 into the mixed stream of resin and catalyst materials from nozzle 1 8 such that the hardened material includes fiber reinforcements that increase strength of the final product.

After a period of operation of spray gun 10 and fiber chopper 12, blades of the cutter blade head and a cutting surface of the anvil head become worn, as the blades become dull from cutting the rovings and the cutting surface becomes lacerated from the blades. However, before such components need to be replaced, the anvil head can be repositioned with respect to the cutter blade head to, among other things, recalibrate the depth of cut of the blades of the cutter blade head into a cutting surface of the anvil head. The adjustable tensioning device of the present invention permits the anvil head to be repositioned with controls accessible from the outside of housing 24 and cover 26, while also automatically controlling the tension between the cutting blades and cutting surface.

FIG. 2A is a perspective view of fiber roving chopper 12 of FIG. 1 showing fixed soft stop 39 and locking mechanism 40 of adjustable tensioning device 52. FIG. 2B is a rear end view of fiber roving chopper 12 of FIG. 1 showing locking mechanism 40 and adjustable hard stop 41 of adjustable tensioning device 52. FIG. 3 A is a perspective view of fiber roving chopper 1 2 of FIG. 1 with cover 26 removed to show cutter blade head 46, anvil head 48 and idler wheel 50. FIG. 3B is a perspective view of fiber roving chopper 1 2 of FIG. 3A with anvil head 48 and idler wheel 50 removed to show slide bar 72 of adjustable tensioning device 52.

As such, adjustable tensioning device 52 comprises fixed soft stop 39, locking mechanism 40 and adjustable hard stop 41 , which are coupled to slide bar 72. The external components of fiber roving chopper 1 2 are shown and discussed with reference to FIGS. 2A and 2B. The internal components and operation of fiber roving chopper 1 2 are shown in and discussed with reference to FIG. 3A, with concurrent reference to FIGS. 2A and 2B. The components of adjustable tensioning device 52 are shown in and discussed with reference to FIG. 3B. Operation of adjustable tensioning device 52 is discussed with reference to FIGS. 4 and 5. Fiber chopper 1 2 includes air motor 22, housing 24, fiber inlets 38, fixed soft stop 39, locking mechanism 40, adjustable hard stop 41 , dispenser chute 42, fasteners 43A and 43B, knob 45, adjustable tensioning device 52 and tube 55. Cutter blade head 46 includes blades 54, blade cartridge 56, spacer spool 58 and retention cap 60. Anvil head 48 includes roller 62, retention cap 64 and fastener 66. Idler wheel 50 includes roller 68 and fastener 70.

With reference to FIGS. 2A and 2B, cover 26 comprises a multi-sided body having an opening that mates with housing 24 to conceal cutter blade head 46, anvil head 48 and idler wheel 50. Cover 26 includes an opening to allow chopped rovings from cutter blade head 46 to be thrown from chopper 12. Dispenser chute 42 mounts to cover 26 with fasteners 43 A and 43 B near the opening to receive chopped rovings from cutter blade head 46. Dispenser chute 42 comprises a three-sided angled plate along which chopped rovings pass after being cut by chopper head assembly 46. The angle of dispenser chute 42 on fasteners 43 A can be adjusted using fasteners 43 B to change the trajectory of the chopped roving pieces. Knob 45 extends into cover 26 to engage tube 55 (FIG. 3A) and retain cover 26 in engagement with housing 24.

With reference to FIG. 3A, cutter blade head 46, anvil head 48 and idler wheel 50 are mounted for rotation on housing 24. Housing 24 comprises a plate against which cutter blade head 46 and anvil head 48 are mounted. Housing 24 include planar cutter surface 24A and edge perimeter 24B. Specifically, cutter blade head 46 is mounted directly onto a drive shaft extending from shaft mechanism 57 (FIG. 2B) of air motor 22, through housing 24, and into retention cap 60. Anvil head 48 and idler wheel 50 are mounted to shafts cantilevered from adjustable tensioning device 52 in housing 24. Fasteners 66 and 70 are typically in threaded engagement with the shafts to retain anvil head 48 and idler wheel 50, respectively.

Adjustable tensioning device 52 comprises a slide bar (FIG. 3 B) that extends into a corresponding slot (FIG. 3 B) in housing 24 between adjustable hard stop 41 and fixed soft stop 39. A spring of fixed soft stop 39 automatically biases the slide bar away from fixed soft stop 39 to push anvil head 48 into contact with cutter blade head 46 at an appropriate pressure to cut fiber rovings. The position of idler wheel 50 with respect to anvil head 48 on the slide bar of adjustable tensioning device 52 is fixed. Movement of the slide bar of adjustable tensioning device 52 moves anvi l head 48 and idler wheel 50 with respect to cutter blade head 46. Adjustment of adjustable hard stop 41 allows for different sized cutter blade heads 46 to be used in chopper 1 2. Additionally, adjustment of adjustable hard stop 41 permits anvil head 48 to be moved to account for degradation of roller 62. Locking mechanism 40 is used to lock the position of the slide bar after adjustment with adjustable hard stop 41 .

Air motor 22 rotates cutter blade head 46 by rotation of a drive shaft that extends from shaft mechanism 57 of air motor 22. Engagement of blades 54 with roller 62 causes anvil head 48 to rotate as well. Anvil head 48 drives rotation of idler wheel 50 through engagement with roller 68. Rovings fed into fiber inlets 38 are grabbed by anvil head 48 and idler wheel 50 and pulled between anvil head 48 and cutter blade head 46. Blades 54 of cutter blade head 46 are pulled into roller 62, which comprises a deformable material. The rovings are sliced between blades 54 and roller 62 as blades 54 rotate anvil head 48 and cut into roller 62. Spacer spool 58 maintains blades 54 at even intervals so that the fibers are consistently cut into similarly sized lengths. Blades 54 and roller 62 become worn and eventually need to be replaced to prevent unacceptable performance degradation of fiber chopper 12. For example, retention caps 64 and 60 are removed to allow roller 62 and blade cartridge 56 to be slid off of their respective mounting shafts with cover 26 removed to perform maintenance. However, before such maintenance is warranted, adjustable tensioning device 52 of the present invention can be employed to advantageously position anvil head 48 closer to chopper blade head 46 to again cut rovings at the desirable depth.

FIG. 3B is a perspective view of fiber roving chopper 12 of FIG. 3 A with anvil head 48 and idler wheel 50 removed to show slide bar 72 of adjustable tensioning device 52 inserted into slot 73. Slide bar 72 includes anvil bore 74, oblong lobe 76, idler bore 78 and lever bore 80. Adjustable tensioning device 52 includes adjustable hard stop 41 located at a first end of slot 73, and fixed soft stop 39 located at second end of slot 73. As such, slot 73 is elongated between hard stop 41 and soft stop 39. Adjustable hard stop 41 includes threaded shaft 82, knob 84 and clip 86. Fixed soft stop 39 includes end stop 88, spring 90 and fastener 92. Adjustable tensioning device 52 also includes locking mechanism 40, which includes shaft 94 and lever 96.

Slide bar 72 is positioned within slot 73 between adjustable hard stop 41 and fixed soft stop 39. Slide bar 72 is thus linearly displaceable between shaft 82 and end cap 88. Spring 90 is positioned between end stop 88 and slide bar 72 to bias slide bar 72 toward hard stop 41 . In other embodiments of the invention, other resilient components or materials, such as a deformable polymer stopper, may be used in place of spring 90. Fastener 92 is threaded into housing 24 so that shaft 82 of hard stop 41 extends into slot 73. The end of shaft 82 limits the amount that spring 90 can push slide bar 72 within slot 73. Clip 86 prevents shaft 82 from being threaded out of housing 24. Threaded shaft 94 of locking mechanism 40 extends through housing 24 to engage threaded bore 80 of slide bar 72. Lever 96 extends from shaft 94 to enable rotation of shaft 94.

A shaft for idler wheel 50 extends from oblong lobe 76 within idler bore 78. Another shaft for anvil head 48 extends from threaded bore 74. As such, the relative position between idler wheel 50 and anvil head 48 is fixed. However, the position of slide bar 72, including anvil head 48 and idler wheel 50, can be adjusted relative to cutter blade head 46 by turning knob 84 of adjustable hard stop 41 , as discussed with reference to FIG. 4.

FIG. 4 is cross-sectional view of adjustable tensioning device 52 taken at section 4— 4 of FIG. 3B showing shafts 98 and 99 for attachment of anvil head 48 and idler wheel 50, respectively, to slide bar 72 of adjustable tensioning device 52. To assemble adjustable tensioning device 52, locking mechanism 40 and soft stop 39 are first removed. Hard stop 41 is installed by threading shaft 82 into threaded bore 100 until the tip of shaft 82 penetrates slot 73. Clip 86 is positioned around shaft 82 near the tip to prevent shaft 82 from being removed from housing 24. Oblong lobe 76 is positioned within oblong slot 101 adjacent idler bore 78 and slide bar 72 is then inserted into slot 73. As shown in FIG. 5, slide bar 72 (and end stop 88) include overhang features to prevent slide bar 72 from being dislodged laterally from slot 73. Spring 90 is inserted into slot 73 to engage bore 102 at the end of slide bar 72. End cap 88 is inserted into slot 73 with bore 104 facing spring 90. Fastener 92 is inserted through aligned bores 106 and 108 in end stop 88 and housing 24, respectively. Bore 106 includes a counter bore to receive a head of fastener 92 so that cover 26 can be fitted to housing 24. As such, spring 90 is put into compression between bore 102 and bore 104. Spring 90 is long enough, or otherwise sized, to remain in compression when threaded shaft 82 of adjustable hard stop 41 is fully retracted within bore 100. That is to say, spring 90 will maintain slide bar 72 engaged with the tip of fastener 82. The force of spring 90 is selected, based on the sharpness of razors 54 of cutter blade head 46 and the resiliency of roller 62 of anvil head 48 (FIG. 3A), to generate enough force to cut fiber rovings without pushing razors 54 completely through roller 62.

Locking mechanism 40 is assembled by first positioning washer 1 09 around threaded shaft 94 and then inserting threaded shaft 94 through adjustment slot 1 1 0 and into threaded bore 80. Shaft 94 secures locking mechanism 40 to slide bar 72. Slot 1 1 0 permits shaft 94 to move within housing 24 while slide bar 72 moves within slot 73. As depicted in FIG. 4, slot 1 10 provides up and down movement of shaft 94 commensurate with linear movement of slide bar 72, while movement in and out of the plane of FIG. 4 is restricted, as discussed with reference to FIG. 5. Washer 109 covers slot 1 10 and permits locking mechanism 40 to slide against housing 24. Washer 109 also permits locking mechanism to pull slide bar 72 into lateral engagement with housing 24 when lever 96 is rotated, as also discussed with reference to FIG. 5.

To complete the assembly of chopper 12, shafts 98 and 99 are inserted through anvil head 48 and idler wheel 50, respectively. Shaft 98 is inserted through a central bore in anvil head 46 and threaded into threaded bore 74. Fastener 66 is attached to shaft 98 to secure anvil head 46 against slide bar 72. Similarly, shaft 99 is inserted through a central bore in idler wheel 50 and threaded into oblong lobe 76. Fastener 70 is attached to shaft 99 to secure idler wheel 50 against slide bar 72. Shaft 99 is tightened to bring lobe 76 into engagement with idler bore 78. Oblong lobe 76 prevents rotation of shaft 99, while the use of oblong slot 101 allows the position of shaft to be adjusted on slide bar 72 with respect to shaft 99. Alternatively, shafts 98 and 99 can be assembled to slide bar 72 before insertion into slot 73.

With lever 96 positioned so as to loosen the engagement between washer 109 and housing 24, slide bar 72 is held in position by the force of spring 90 and adjustable hard stop 41 . Fastener 108 holds end cap 88 firmly in place so that spring 90 pushes slide bar away from end cap 88. Spring 90 pushes anvil head 48 into cutter blade head 46 at a pressure or tension suitable for the type of fiber rovings to be cut and dispensed. Knob 84 is then tightened to thread shaft 82 into bore 100 to engage slide bar 72 and prevent further ingress of blades 54 into roller 62. Finally, lever 96 of locking mechanism 40 is rotated to prevent movement of slide bar 72 during operation of chopper 12. For example, blades 54 would have a tendency to push anvil head 46 away from cutter blade head 46 during rotation, which would compress spring 90. Additionally, threaded shaft may vibrate out of position during operation of chopper 12, causing slide bar 72 to be further pushed by spring 90. Locking mechanism 40 prevents slide bar 72 from moving during these events.

FIG. 5 is an end cross-sectional view of adjustable tensioning device 52 taken at section 5-5 of FIG. 3 B showing overhang feature 1 1 2 for retaining slide bar 72 laterally within slide slot 73. In addition to overhang feature 1 1 2, slot 73 comprises sl ide surface 1 14, while slide bar 72 includes flange 1 1 6 to mate with overhang feature 1 1 2. As mentioned, slide bar 72 is inserted into slot 73 in the linear direction. Further linear movement of slide bar 72 into the plane of FIG. 5 is limited by hard stop 4 1 , while linear movement of slide bar 72 out of the plane of FIG. 5 is limited by soft stop 39. Lateral movement of slide bar 72 to the right is limited by slide surface 1 14, while lateral movement to the left is limited by engagement of flange 1 1 6 with overhang feature 1 16. In the embodiment shown, overhang feature 1 12 give slot 73 a T-shaped profile. In other embodiments, other shapes may be used, such as a dovetail shape or a fir tree shape.

With locking device 40 loosened, slide bar 72 is free to travel linearly within slot 73 along slide surface 1 14. Shaft 94 of locking mechanism 40 thereby is pulled along within slot adjustment slot 1 10. As discussed with reference to FIG. 4, slot 1 10 permits such linear movement of shaft 94, but limits movement of shaft 94 in an up and down (with reference to FIG. 5) manner. Slot 1 10 is, however, sized to not inhibit movement of locking mechanism of slide bar 72, as ultimate movement of shaft 94 is limited by movement of slide bar 72 within slot 73. When slide bar 72 is moved to the desired position, lever 96 of locking mechanism 40 is rotated to thread shaft 94 into bore 80, thereby pulling slide bar 72 laterally into engagement with slide surface 1 14 of slot 73 and immobilizing slide bar 72. Washer 109 permits locking mechanism to rotate smoothly against housing 24.

The present invention provides an adjusting system for rotating heads in a fiber roving chopper. The distance between a cutter blade head and an anvil head can be manually set by turning an adjustment knob located on an exterior of the chopper. As such, the chopper need not be disassembled to make the adjustment. The adjusting system includes a spring bias to push the anvil head into the cutter blade head at a preset pressure or tension. As such, an operator of the chopper does not have to select how close to move the anvil head to the cutter blade head. With the biasing spring holding the heads in engagement, the operator can engage an externally activated locking mechanism to temporarily immobilize the anvil head and enable operation of the chopper. After operation of the chopper in which the anvil head experiences degradation that undesirably affects the length of the cut fiber strands, an operator, after stopping operation of the chopper, only has to release the locking mechanism and loosen the adjustment knob to bring the anvil head closer to the cutter blade head. The biasing spring ensures the proper blade pressure against the anvil, thereby increasing the life of the razor blades. The locking mechanism can be reengaged to resume operation of the chopper.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS:

1 . A tensioning device for adjusting position between rotatably engagable chopper heads, the tensioning device comprising:

a mounting plate comprising:

a planar surface against which heads are configured to rotate; and an slot disposed in the planar surface and having a slide surface extending from a first end to a second end;

a slide bar disposed within the slot between the first and second ends, the slide bar being linearly displaceable along the slide surface;

an adjustable hard stop disposed at the first end of the slot to limit linear displacement of the slide bar;

a fixed soft stop disposed at the second end of the slot to bias the slide bar toward the adjustable hard stop;

a locking device for immobilizing the slide bar within the slot; a first shaft extending from the slide bar; and

a first chopper head coupled to the first shaft.

2. The tensioning device of claim 1 and further comprising:

a drive motor coupled to the mounting plate;

a drive shaft extending form the drive motor and through the mounting plate; and

a second chopper head coupled to the drive shaft;

wherein the slide bar moves within the slot to vary a distance between the first chopper head and the second chopper head.

3. The tensioning device of claim 2 wherein:

the slide bar includes a threaded bore; and

the first shaft is threaded into the threaded bore.

4. The tensioning device of claim 2 and further comprising:

a second shaft including an oblong lobe;

an idler wheel coupled to the second shaft; and

an oblong shaft bore disposed with in the slide bar for receiving the second shaft;

wherein the oblong lobe fits into the oblong shaft bore to prevent rotation of the second shaft.

The tensioning device of claim 1 wherein:

the mounting plate comprises an edge perimeter surrounding the planar surface; and

the slot comprises a profile that extends into the edge perimeter at the second end and extends to the first end to form the slot, the profile including an overhang feature such that the slide bar is limited in displacement from slide surface.

The tensioning device of claim 5 wherein the profile comprises a T-shape.

The tensioning device of claim 5 wherein the hard stop comprises:

a threaded bore extending into the edge perimeter of the mounting plate at the first end; and

a threaded shaft extending through the threaded bore into the slot;

wherein the threaded bore and the threaded shaft extend parallel to the slide bar.

The tensioning device of claim 7 wherein the threaded shaft further a knob connected to the threaded shaft outside of the slot; and

a clip connected to the threaded shaft inside of the slot.

The tensioning device of claim 5 wherein the soft stop comprises:

a cap extending into the slot from the edge perimeter at the second end;

a fastener securing the cap to the mounting plate; and

a spring positioned between the cap and the slide bar;

wherein the spring extends parallel to the slide bar.

The tensioning device of claim 9 and further comprising:

a first bore extending into the cap parallel to the planar surface into which the spring extends; and

a second bore extending into the cap perpendicular to the first bore to engage the mounting plate.

The tensioning device of claim 1 wherein the lock device comprises:

a threaded bore extending into the slide bar;

a slot extending into the mounting plate adjacent the threaded bore;

a washer having a diameter taller than the slot positioned adjacent the threaded bore; and a threaded fastener extending through the washer and slot to engage the threaded bore in the slide bar.

12. The tensioning device of claim 1 1 wherein the threaded fastener comprises:

a shaft extending into the slide bar; and

a lever connected to the shaft;

wherein rotation of the lever threads the threaded fastener into the threaded bore to bring the slide bar into engagement with the slide surface.

13. The tensioning device of claim 1 and further comprising:

a cover coupled to the mounting plate so as to enclose the slot and the slide bar in an interior of the cover;

wherein the adjustable hard stop and the lock device include grips located external to the cover.

14. A roving chopper comprising:

a drive motor having a drive shaft;

a chopper blade head;

an anvil head;

a mounting plate comprising:

a drive surface against which the drive motor mounts;

a chopper surface against which chopper blade head and anvil head are mounted;

a drive bore extending from the drive surface to the chopper surface and through which the drive shaft extends; and

a slot disposed on the internal surface;

a slide bar disposed within the slot so as to be linearly displaceable between a first end and a second end;

a hard stop located at the first end to adjustably limit linear movement of the slide bar;

a soft stop located at a second end of the slot to bias the slide bar toward the hard stop: and

a locking device for immobilizing the slide bar within the slot.

1 5. The roving chopper of claim 14 wherein:

the mounting plate comprises an edge perimeter surrounding the planar surface; and the slot comprises a profile that extends into the edge perimeter at the second end and extends to the first end to form the slot, the profile including an overhang feature such that the slide bar is limited in displacement from slide surface.

16. The roving chopper of claim 15 wherein the hard stop comprises:

a threaded shaft extending through the threaded bore into the slot;

1 7. The roving chopper of claim 1 5 wherein the soft stop comprises:

a cap extending into the slot from the edge perimeter at the second end;

a fastener securing the cap to the mounting plate; and

a spring positioned between the cap and the slide bar;

wherein the spring extends parallel to the slide bar.

1 8. The roving chopper of claim 1 5 wherein the lock device comprises:

a threaded bore extending into the slide bar;

a slot extending into the mounting plate adjacent the threaded bore;

a washer having a diameter taller than the slot positioned adjacent the threaded bore; and

a threaded fastener extending through the washer and slot to engage the threaded bore in the slide bar.

19. The roving chopper of claim 14 and further comprising:

a chopper cover coupled to the mounting plate and having an interior that encloses the slot and the slide bar;

wherein the adjustable hard stop and the lock device include grips located external to the chopper cover.