Abstract:
A rotary cutter apparatus uses an improved geometrical arrangement of parts to optimize cutter speed versus evenness and straightness of cut, increase operating life and quietness of operation, and reduce dust formation and energy consumption.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This non-provisional application for patent claims priority to copending PCT Application No. PCT/US10/55792, published as Publication No. WO 2012/064320, which is incorporated herein in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not applicable. 
       REFERENCE TO A BIOLOGICAL SEQUENCE LISTING 
       [0004]    Not applicable. 
       BACKGROUND OF INVENTION 
       [0005]    Field of the Invention 
         [0006]    This invention is in the field of cutters, more specifically in the field of cutters with intersecting blades, and still more specifically in the field of motor-driven cutters of sheet material. 
         [0007]    Description of the Related Art 
         [0008]    Many consumable products are manufactured in the form of spirally-wound rolls, e.g., paper towels and gift wrap. While these products can be unwound from the roll entirely by hand, there are a number of devices in the prior art to aid in dispensing product from the roll. These range from simple support of the roll, such as a single upright spindle upon which the axis of the roll is vertically installed, to cabinets into which a product roll is placed and which have mechanisms for dispensing product. 
         [0009]    For simplicity of further discussion, and because the most common product roll dispensed is paper or similar nonwoven web material, the terms “paper,” “paper towel” and “paper towel roll” will be used hereinafter instead of “product” and “product roll.” However, it should be understood that the present invention can be adapted to virtually any spiral-wound sheet product. 
         [0010]    Until the issue of U.S. Pat. No. 6,994,408 to the present inventor, a problem with dispensers of the art prior to U.S. Pat. No. 6,994,408 was that parts driven at high speed were stopped by surfaces, such as bumpers, in the machine, which led to excessive noise and impact wear. 
         [0011]    The cutting mechanism of that device is a circular blade slicing product along a horizontal linear blade. The circular blade rotates on an axle that moves in a direction parallel to the linear blade, with its axle tilted so that the leading edge of the circular blade is higher than the trailing edge. The rotation of the circular blade causes the leading edge of the circular blade to rotate toward the linear blade. In other words, if the circular blade is beneath the linear blade and the axle of the circular blade is moving from right to left, the upper end of the axle is tilted to the right, the leading edge of the circular blade is tilted upward, and the product is sheared against the linear blade. 
         [0012]    The circular blade is made to rotate by an o-ring mounted on the same axle which presses against a fixed horizontal surface parallel to the linear blade. The function of cutting paper with the rotary cutter method is affected by a combination of variables including the angle of attack of the circular blade, the hardnesses of the blades, the pressure between the blades, the pressure of the o-ring against the horizontal surface, and the spinning speed of the circular blade. After thousands of tests, data show that the instant invention offers superior durability and repeatability, and that any one change can alter performance dramatically. 
         [0013]    The reason for tilting the axle relative to the direction of travel originally was to prevent binding of the paper between the blades and galling of the blades. The reason for using a resilient o-ring to drive the cutter was to reduce noise and allow the drive mechanism to skid at that point and to assure consistent forward motion of the cutter without stripping its toothed rubber drive belt. Since issuance of that patent, these basic configurations have been validated, but they have been refined by extensive experimentation. 
       BRIEF DESCRIPTION OF THE INVENTION 
     Objects of the Invention 
       [0014]    Needs addressed by the present invention are reduction in operating noise and vibration, improved resistance to cutter edge wear, reduction in dust formation, and improved operating life. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention is a rotary cutter apparatus that optimizes cutter speed versus evenness and straightness of cut, operating life, quietness of operation, and low dust formation. These and other benefits will become more clearly illustrated in the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an oblique view from the upper left front of a product roll cutter containing the present invention as it operates during the leftward pass of the cutting sequence. 
           [0017]      FIG. 2  is a simplified oblique view of the key parts of the present invention operating in the same orientation as depicted in  FIG. 1 . 
           [0018]      FIG. 3  is a top view of the key parts shown in  FIG. 2 . 
           [0019]      FIG. 4  is a diagram of the geometry of the key parts shown in  FIG. 3 . 
           [0020]      FIG. 5  is a left end view of the key parts shown in  FIG. 2 . 
           [0021]      FIG. 6  is a front view of the key parts shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring now to the attached drawings, in which like features are represented by like reference characters in each of the drawings,  FIG. 1  is an oblique view from the upper left front of the product roll cutter as described in copending PCT Application No. PCT/US10/55792 by the same inventor. A product roll of paper  1  has been advanced by drive roller  2  to the position shown. A cutter carousel  4  is shown in the process of cutting paper  1  from right to left in this drawing. Its case  5  is cut away to show a circular paper cutting blade  6 , an optional pinion  91 , and a rubber o-ring  7  mounted on a cutter dowel pin  8 . Hereafter in the present application, the term “carousel,” unless otherwise specified, minimally consists of circular paper cutting blade  6 , either pinion  91 , rubber o-ring  7  or both, all rotatably mounted on a cutter dowel pin  8 , and all held at a fixed orientation with respect to X, Y, and Z axes but movable along the X axis. 
         [0023]    The features and description of this patent application are also to be understood to include the mirror image of what is described, that is, what enables building the invention from the instant description is also intended to enable building its mirror image. For example, carousel motion from right to left causing clockwise circular blade rotation as viewed from above expressly includes carousel motion from left to right causing counterclockwise circular blade rotation as viewed from above. 
         [0024]    An upper pinch plate  20  in a substantially vertical plane, an optional rack  92  fixed to upper pinch plate  20 , and an upper backing plate  10  are also shown. Upper pinch plate  20  and upper backing plate  10  function to grip paper  1  above a stationary horizontal straight cutting blade  9 . A lower backing plate  11  and a lower pinch plate  12  function likewise to grip paper  1  below straight blade  9 . 
         [0025]    Carousel  4  is moved horizontally left and right by a belt (not shown) driven by an electric cut motor (not shown) as described in PCT Application No. PCT/US10/55792. As carousel  4  moves to the left, the rubber o-ring  7  contacts the upper pinch plate  20 . Upper pinch plate  20  is pushed rearward by the rubber o-ring  7 , pinching the paper  1  against the upper backing plate  10 . Friction of the o-ring  7  against the upper pinch plate  20  drives the circular paper cutting blade  6  clockwise (as viewed from above) about the cutter dowel pin  8 . Optionally, a pinion  91  may be installed upon the cutter dowel pin  8 , for the purpose of engaging an optional rack  92  fixed to the front side of the upper pinch plate  20  to provide positive forced rotation of the circular blade  6  about the cutter dowel pin  8 . 
         [0026]      FIG. 2  is a simplified oblique view of the key parts of the present invention operating in the same orientation as depicted in  FIG. 1 . The key parts are: circular blade  6 , o-ring  7 , and cutter dowel pin  8  about which they rotate (the “carousel”); upper pinch plate  20 ; and straight blade  9 . Circular blade  6  has a circular cutting edge  71 , and straight blade  9  has a straight cutting edge  72 . The point where the cutting edges meet, the cutting point  40 , is of course where the paper is cut.  FIG. 2  shows circular blade  6  rotating clockwise in path A, contacting straight blade  9  from below and moving from right to left in direction B. It is within the scope of this invention for circular blade  6  to contact straight blade  9  from above, rotate counterclockwise, and move from left to right. 
         [0027]    Important Characteristics of the Present Invention: 
         [0028]    I. The Net Velocity of the Point of Contact of the Circular Blade with the Straight Blade in the Horizontal Direction Must be Approximately Zero. 
         [0029]      FIG. 3  is a top view of the parts shown in  FIG. 2 . Pinch plate  20  needs to be approximately vertical to allow for slight variations in the path of contact between it and o-ring  7 . Although pinch plate  20  need not be precisely vertical, it is shown that way in this and the remaining drawings for better visualization and explanation of the relative orientation of the parts. In  FIG. 3 , the vertical direction is pointing out of the page, and the carousel, namely circular blade  6 , o-ring  7 , and cutter dowel pin  8  are all being driven from left to right in the horizontal direction by a drive belt (not shown). Because o-ring  7  is being pressed against stationary pinch plate  20 , the rotational speed (in rpm) of dowel pin  8  is the same as that of o-ring  7 . PCT Application No. PCT/US10/55792 by the present inventor states that because the rubber o-ring  7  is of smaller diameter than circular blade  6 , the edge of the circular blade  6  is forced to move relative to straight blade  9  (leftward in  FIG. 3 ) adding a (leftward) shear component to what would otherwise be a purely downward (in  FIG. 3 ) shear component against the paper, and that these two effects produce a clean cut and minimize the creation of paper dust. However, the fact that o-ring  7  is of smaller diameter than circular blade  6  does not necessarily result in a slicing action parallel to straight blade  9 . Further experimentation has shown that a leftward (or rightward) component of motion at the point of contact  40  can cause the sheet product to bunch, tearing the sheet or producing an uneven cut, and/or can cause the blades to separate and jam because of product being forced in between them. As it happens, the left and right components of velocity of contact point  40  in the present invention approximately cancel each other (so that the blades approach each other along a vertical line in this view) only if the sum of the o-ring radius plus the length of the normal from the stationary blade to the circular blade edge equals the radius of the circular blade. This is proven by the following calculations. 
         [0030]      FIG. 4  is a diagram of the geometry of the blades of  FIG. 3  under the simplifying assumption that the circular blade  6  and the o-ring  7  are both coplanar with straight blade edge  72 , in which case the left and right components exactly cancel, as follows:
       Forward (rightward) horizontal velocity of dowel pin  8  and point  40 =v f =V;   peripheral velocity of point  40 =v p =VR/r; and   reverse horizontal velocity of point  40 =v r =v p (R−s)/R=(VR/r)(R−s)/R=V(R−s)/r.   For v f =v r , V=V(R−s)/r;
           therefore R=r+s.   
               
 
         [0036]    This means that point  40  will move exclusively downwardly (in this view) across straight blade edge  72  only if blade edge  72  coincides with front surface of upper pinch plate  20 . This fact, in combination with test results to arrive at the optimal circular blade and o-ring radii (see item II. following) further define the optimum geometry represented by the present invention. (In some models of this invention, the upper pinch plate  20 , which o-ring  7  rides on, is closer to the axle  8  than the horizontal blade  72  by a small distance as shown in  FIG. 3  to allow for the sheet product to hang between the back of the pinch plate and the horizontal blade. Unless the pinch plate is shaped to allow a larger o-ring radius, this small distance will cause a small net leftward component in the motion of the circular blade edge  71  at point  40 . 
         [0037]    II. Other Cutter Parameters are Necessary to Produce a High-Quality Cut and Protect Cutter Durability. 
         [0038]    A high transverse speed of the cutter carousel is desirable for a fast cut, but it must be limited to control impact forces and noise. Experimentation by the inventor has shown that for these reasons, the optimum left-to-right speed V of the cutter (as shown in  FIG. 4 ) should not exceed about 0.6 m/s. A circular blade radius R of 18.5 mm was chosen as the maximum for a reasonably compact assembly. Experimentation showed that unexpectedly superior cut quality, machine durability, reduced noise and minimal dust production were produced by using an o-ring radius r of 11.4 mm (61.6% of the circular blade radius) and observing the geometry described in item I. above. The corresponding calculations are given in Table 1 below: 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Cutter Forward Travel 
                 T (Chosen by experiment) 
                 475 
               
               
                   
                 Time, ms 
                   
                   
               
               
                   
                 Cutter Travel Distance, 
                 D (Measured on machine) 
                 286 
               
               
                   
                 mm 
                   
                   
               
               
                   
                 Maximum Horizontal 
                 V = D/1000T 
                 602 
               
               
                   
                 Cutter Velocity, mm/s 
                   
                   
               
               
                   
                 Maximum Circular Blade 
                 R (Chosen by experiment) 
                 18.5 
               
               
                   
                 Radius, mm 
                   
                   
               
               
                   
                 Maximum O-Ring 
                 r (Chosen by Experiment) 
                 11.4 
               
               
                   
                 Radius, mm 
                   
                   
               
               
                   
                 Optimum Ratio of O- 
                 r/R 
                 0.616 
               
               
                   
                 Ring Radius to Circular 
                   
                   
               
               
                   
                 Blade Radius 
                   
                   
               
               
                   
                 Cutter Assembly 
                 S = 60 V/2πr 
                 504 
               
               
                   
                 Rotation Speed, rpm 
                   
                   
               
               
                   
                 Cut Angle (Angle of 
                 α = 180cos −1 (r/R)/π  
                 52 
               
               
                   
                 Tangent to Circular Blade 
                 (see FIG. 4) 
                   
               
               
                   
                 at Cut Point relative to 
                   
                   
               
               
                   
                 Straight Blade), Degrees 
                   
                   
               
               
                   
                 Velocity of Cut Point on 
                 V v  = Vπ(sin(α))/180)  
                 474 
               
               
                   
                 Circular Blade 
                 (see FIG. 4) 
                   
               
               
                   
                 Perpendicular to Straight 
                   
                   
               
               
                   
                 Blade, mm/s 
               
               
                   
                   
               
             
          
         
       
     
         [0039]    III. The O-Ring Diameter Must be Large Enough Not to Skid Against Upper Pinch Plate. 
         [0040]    As shown in  FIG. 1 , circular blade  6  could be driven by a pinion  91  engaging a rack  92  rather than, or in addition to, an o-ring  7  frictionally engaging upper pinch plate  20 . Even though the rack-and-pinion is an embodiment of the present invention, the o-ring drive option is the preferred embodiment. Two of the reasons the inventor chose to drive circular blade  6  with a resilient o-ring  7  rather than a pinion is (i) less noise and (ii) less potential damage in the event the blades seize. If a rubber o-ring alone is used to drive circular blade  6  (as it is in the preferred embodiment) the rolling friction between the rubber and the pinch plate must be less than the sliding friction to assure that the o-ring dependably rolls rather than skids along the pinch plate. 
         [0041]    For a given force W of the o-ring against the plate, the sliding or dynamic frictional force F d  necessary to initiate skidding is F d =f d W, where f d  is the dynamic friction factor for rubber against the upper pinch plate material. The dynamic friction factor is used instead of the static friction factor because (as described in copending PCT Application No. PCT/US 10/55792) o-ring  7  begins spinning upon first contact with the right-hand edge of upper pinch plate  20 , before it presses the pinch plate rearwardly in the machine, and it is therefore already rotating as it begins rolling along the vertical surface of the pinch plate  20 . Estimates of the dynamic friction factor range from 0.5 (see http://www.tribology-abc.com/abc/cof.htm) to 3-4 (see http://nvlpubs.nist.gov/nistpubs/jres/28/jresv28n4p439_Alb.pdf), an average of 2.0 (dimensionless). The rolling frictional force F r  necessary to initiate rolling is F r =f r W/r, where r is the radius of the o-ring and f r  is the rolling friction factor for the o-ring against the pinch plate (expressed in length units). An estimate of this is 0.0077 meters, or 7.7 mm (see www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm#coef). To assure that rolling will occur instead of skidding, F r &lt;F d , or f r W/r&lt;f d W Interestingly, the force W of the o-ring against the plate cancels out. Rearranging, r&gt;f r /f d &gt;7.7 mm/2.0=3.8 mm. Thus, by this measure, the radius of the o-ring r must be greater than about 4 mm to prevent skidding. The optimal o-ring radius selected by experiment as given in Table 1 is 11.4 mm, so the minimum radius of the o-ring is not limiting in the design of the cutter. 
         [0042]    IV. The Shape of the Cutting Edges Should be Right Angles. 
         [0043]    In  FIG. 5  it can be seen that the cross-sections of cutting edges  71  and  72  are the vertices of right angles. The reason for this is that an acute angle on either blade is more prone to chipping, spalling, and earlier dulling. An obtuse angle is undesirable simply because it is less sharp and tends to pinch and tear the sheet rather than cutting it. This creates an uneven cut and dust. 
         [0044]    V. Other Criteria are Necessary to Enable Self-Sharpening. 
         [0045]      FIG. 3  is a top view of the parts shown in  FIG. 2 . Although pinch plate  20  need not be precisely vertical, it is shown that way in this illustration and in  FIGS. 5 and 6  for better visualization and explanation of the relative orientation of the parts. As mentioned in PCT Application No. PCT/US10/55792, the experimentation done by the inventor at that time found that cutting action is enhanced by tilting the stationary paper cutting blade  9  downward toward the front of the invention (toward the right in  FIG. 5 ) by about 5 degrees (angle β) and by inclining circular blade  6  clockwise (angle γ in  FIG. 6 ) in a range of about 3 to 7 degrees. More recent testing has expanded this range to between 2 and 7 degrees. 
         [0046]    Further experimentation has borne this out, but shows that the hardness of straight blade  9  is critical and must be set to 52 Rockwell C minimum. (Harder materials may be used but are more expensive.) Moreover, if straight blade  9  is harder than circular blade  6  by at least 4 Rockwell C points, it becomes self-sharpening. The vertex of the right angle at straight cutting edge  72  at cutting point  40  (like any real-world knife edge) is not a geometric point but a rounded edge, that is, a quarter circle of an extremely small radius. The softer metal of circular blade  6  actually maintains the rounded edge of straight cutting edge  72  at the expense of metal loss at circular cutting edge  71  provided the contact angle β is no greater than about 5 degrees, and angle γ is no greater than about 7 degrees. An angle greater than 5 degrees increases the incidence of galling on the circular cutting edge  71  (that is, the softer metal forming small lumps that adhere to and distort the edge rather than dissipating as an aerosol). An angle greater than 7 degrees significantly increases the carousel drive motor power requirement. (Note that these angles are low and do not materially affect the calculations in items I-III above.) From the standpoint of cut quality and dust production, it is more important that the straight cutting edge  72  remain perfectly straight than that the circular cutting edge  71  be perfectly round. The round blade will cut paper even if it is slightly uneven in radius provided cutting edge  71  remains planar. 
         [0047]    VI. The Tilt of the Cutter Carousel Must be Within a Certain Range to Control the Shear Pressure Between the Blades and Minimize the Power Consumption. 
         [0048]    It is important to maintain adequate upward pressure between circular blade  6  and straight blade  9  to prevent the blades from separating and becoming jammed because of uncut product being forced in between them. PCT Application No. PCT/US10/55792 teaches placing two springs at the end of a carousel track to bias the cutter carousel rearwardly and upwardly.  FIG. 5  in the present application shows a force diagram in which the springs (represented here by spring  44  anchored within support structure  15 ) exert a horizontal force F a  against the carousel which not only drives o-ring  7  but also produces upward force F b  on circular blade  71  by virtue of lever arms D 1  and D 2  acting about the fulcrum of o-ring contact point  50 . This upward force F b  is reduced by the ratio of the o-ring radius r to circular blade radius R. (Specifically, F b =F a (D 1 r)/R(D 1 -D 2 )). The upward force F b  created by the springs is augmented by an upward pull F a  on circular blade  6  caused by the tilt of the o-ring drive mechanism, better shown in  FIG. 6 . Upward pull F a  is also a function of the force F a  pressing o-ring  7  against upper pinch plate  20  and the clockwise inclination (see angle γ in  FIG. 6 ) of o-ring  7 . Angle γ makes o-ring  7  “walk upwardly” against upper pinch plate  20  as it travels from right to left across it, and the greater the angle, the greater the upward pull. The upward pull at cutting point  40  is the same force F a  because cutter dowel pin  8  is constrained by its bearings within the carousel housing. 
         [0049]    The spring bias F a  in  FIG. 5  has been set by experiment so that the combination of spring upward force F b  and o-ring upward force F a  produces the best cut if angle γ is about 5 degrees. Angle γ can be below this range if the bias of spring  44  is increased, but experimentation has shown that it must not be less than 2 degrees. A lesser angle causes fouling between circular blade  6  and straight blade  9 . An angle γ over 7 degrees requires too much power, the excess of which is more than necessary to roll the o-ring and merely grinds the circular blade against the straight blade after the sheet product is cut. 
         [0050]    The same principles apply if, in embodiments, a rack-and-pinion mechanism is used with, or instead of, the o-ring system. However, the more dependence is placed on the rack-and-pinion, the greater the bias of the springs  44  needs to be above that of the preferred embodiment to achieve the necessary pressure between the blades. If the o-ring is eliminated, the effective diameter of the pinion teeth must be equal to the diameter of the o-ring in accordance with Table 1, and the upper pinch plate must be moved rearwardly in the unit to allow for the thickness of the rack.