Abstract:
A grass cutting machine using flail-type centrifugally stiffened blades ( 32 ) pivotally mounted on a cutter hub ( 30 ) on a motor shaft ( 28 ). The cutter and a motor assembly ( 20, 22 ) are mounted on wheels ( 42 ). Preferably the cutter rotation axis is parallel to the direction of travel. This efficiently sculpts a concave channel ( 62 ) in grass as the machine is rolled across a lawn ( 60 ). A laterally extending guide tube ( 46 ) may be attached to the machine to visually guide a user in cutting a channel parallel to a previously cut channel.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to methods and machines for creating artistic patterns in lawns, and also to machines for cutting lawns.  
         [0003]     2. Description of Prior Art  
         [0004]     Various types of grass cutting technologies are known, including a horizontal rotating blade known as a rotary mower, a horizontal helical shearing cutter known as a reel-type mower, and rotating flails of several types, such as a flexible cord extending radially from a rotating hub and stiffened by centrifugal force. Flails also include rigid or semi-rigid blades or cords that are pivotally attached to a rotating hub, and are urged into radial orientation by centrifugal force. An advantage of flails is that they can withstand contact with solid objects such as walls, landscaping borders, tree roots, etc., with less damage to the solid object and less damage to the cutter than with rigid blades.  
         [0005]     Grass playing fields for professional sports are often prepared by lawn keepers to show geometric patterns such as circles, lines, letters, and portraits. A common way of doing this is to mow the grass using a reel-type mower with a roller behind the cutter that bends the grass leaves in the direction of travel. The mower is used in different directions to make the grass appear in patterns of darker and lighter stripes. Where the grass leans toward an observer, it appears darker. Where it leans away from an observer, it appears lighter. Rotary mowers can also be used if they have a following roller. However, reel-type mowers produce a cleaner and more uniform cut that can be more uniformly bent by a roller.  
         [0006]     Another pattern-making method is to mow a field uniformly with a reel or rotary type mower, then make a pattern in the grass using rollers only. For example, in the pattern-making stage, a mower with rollers can be used with the cutter turned off, so only the rollers are used. This method makes it easier to cut the lawn evenly without missing spots, then concentrate on the route for making the pattern.  
       SUMMARY OF THE INVENTION  
       [0007]     An objective of this invention is to provide a lawn sculpting machine that efficiently cuts channels of shorter grass in a previously mowed lawn to produce artistic patterns on the lawn.  
         [0008]     This objective is met with a grass cutter using flail-type centrifugally stiffened blades pivotally mounted on a cutter hub on a motor shaft. The cutter and a motor assembly are mounted on wheels. Preferably the cutter rotation axis is parallel to the direction of travel. This efficiently sculpts a concave channel in grass as the machine is rolled across a lawn. A laterally extending guide tube may be attached to the machine to visually guide a user in cutting a channel parallel to a previously cut channel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic view of a first design concept for cutting grooves in grass;  
         [0010]      FIG. 2  is a schematic view of a second design concept for cutting grooves in grass;  
         [0011]      FIG. 3  is a schematic view of a preferred design concept for cutting grooves in grass;  
         [0012]      FIG. 4  is a perspective view of a multiple cutter hub array.  
         [0013]      FIG. 5  is a front view of the multiple cutter hub array of  FIG. 4 .  
         [0014]      FIG. 6  is a top sectional view of a grass sculpting machine according to aspects of the invention, taken on a section plane through the axis of the motor shaft;  
         [0015]      FIG. 7  is a perspective front view of a machine as in  FIG. 6  with the motor turned off;  
         [0016]      FIG. 8  is a top view of a machine as in  FIG. 6  cutting a parallel line on a lawn using a guide tube. 
     
    
     REFERENCE CHARACTERS  
       [0017]      20 . Motor case  
         [0018]      22 . Motor or engine  
         [0019]      24 . Cooling air  
         [0020]      26 . Cooling air inlet filter  
         [0021]      28 . Motor shaft  
         [0022]      29 . Shaft rotation  
         [0023]      30 . Cutter hub  
         [0024]      30 A. First cutter hub in a multiple cutter hub array  
         [0025]      30 B. Second cutter hub in a multiple cutter hub array  
         [0026]      30 C. Third cutter hub in a multiple cutter hub array  
         [0027]      30 D. Fourth cutter hub in a multiple cutter hub array  
         [0028]      32 . Cutter blade or flail  
         [0029]      32 A. Cutter blade on first cutter hub in multiple cutter hub array  
         [0030]      32 B. Cutter blade on second cutter hub in multiple cutter hub array  
         [0031]      32 C. Cutter blade on third cutter hub in multiple cutter hub array  
         [0032]      32 D. Cutter blade on fourth cutter hub in multiple cutter hub array  
         [0033]      34 . Cutter flail pivot pin  
         [0034]      36 . Air impeller  
         [0035]      38 . Cutter safety shroud  
         [0036]      40 . Cutter discharge chute  
         [0037]      42 . Wheel  
         [0038]      44 . Axle  
         [0039]      46 . Cutting guide tube  
         [0040]      48 . Cutting guide pivot  
         [0041]      50 . Cutting guide extension adjustment  
         [0042]      52 . Handle tube  
         [0043]      54 . Handle bar  
         [0044]      60 . Grass  
         [0045]      62 . Groove cut into grass  
       DETAILED DESCRIPTION  
       [0046]      FIG. 1  shows a schematic view of a first type of cutter, in which blades or flails  32  are mounted on a vertical shaft  28 . The cut profile  62  produced by this design has a rectangular shape. The corners of this profile can be rounded slightly with a curved blade. However, a concave arcuate profile as later described is impractical with the design of  FIG. 1 , because a fully arcuate blade would not cut grass near the shaft. Also, flail-type cutting elements  32  cannot provide a circular arcuate geometry in the configuration of  FIG. 1 , even if the flail elements are rigid, because centrifugal force will cause them to extend horizontally from the pivot pin  34  based on their average mass density, rather than curve upward.  
         [0047]      FIG. 2  shows a schematic view of a second type of cutter, in which blades or flails  32  are mounted on a horizontal shaft that is transverse to the travel direction. This configuration can produce any type of cut profile  62  based on the curvature of the blade edges. However, cutting efficiency is low for two reasons: 1) the grass is cut repeatedly shorter and shorter as the cutter advances. Thus, the grass is cut many times, rather than just once. 2) If the blade edge is curved, its speed will vary with radial distance from the axis. The blade must rotate fast enough to effectively cut grass at the shortest part of the blade. This gives excess speed to the longest part of the blade, causing excess air resistance.  
         [0048]     The configuration of  FIG. 3  has none of these disadvantages, and is the preferred embodiment of this invention. Blades or preferably flails  32  are mounted on a horizontal rotary shaft  28  that is aligned with the direction of travel. A motor or engine  22  drives the rotary shaft  28 . Herein “motor” means any rotary drive means, such as an electric motor as shown or an internal combustion engine. The motor and other parts may be assembled on a chassis or frame (not shown) or the motor case  20  may provide attachment points for the other parts for example by bolts. In the claims “attached to the motor case” means directly or indirectly attached, for example by attachment to another part that is directly or indirectly attached to the motor case. The flails  32  are mounted on pivot pins  34 , and extend radially from a cutter hub  30  under centrifugal force. The pivot pins  34  may for example be in the form of shoulder pins with a narrowed threaded end, as shown in  FIG. 6 .  
         [0049]      FIGS. 4 and 5  show a multiple hub cutter array that can be used in the orientation of either  FIG. 2  or  FIG. 3 . A plurality of hubs  30 A,  30 B,  30 C,  30 D are mounted in an axial sequence on a common shaft  28 . Each hub has respective blades  32 A,  32 B,  32 C,  32 D. Each hub is rotationally offset from the adjacent hub as shown. The number of hubs, blades per hub, and the offset angles may vary.  
         [0050]     The distal ends of the rotating flails  32  describe a cutting circle. A safety shroud  38  surrounds at least a part of cutting circle, including radially around it except below it. A discharge chute  40  extends from the shroud to discharge grass cuttings. An air impeller  36  is attached to the cutter hub  30  to provide air flow  24  for grass discharge. The impeller may also provide air flow to cool the motor. For example an electric motor  22  may be arranged as shown in  FIG. 6  with air filters  26  in back of the motor case  20  for inlet air  24 . This air flow passes over the motor and then forward through the impeller  36  and out the discharge chute  40 .  
         [0051]     A handle tube  52  may be provided with a proximal end attached to the motor case or chassis. The handle tube has a distal end with a handle bar  54  for pushing the sculpting machine in a direction of travel. At least two transport wheels  42  are mounted on respective parallel axles  44  attached to the motor case or chassis. Preferably two transport wheels  42  are mounted on opposite ends of a single axle  44  as shown. In the claims, the term “substantially parallel axles” includes the situation in which a single axle is used for two wheels. A two-wheel configuration as shown allows the user to make cutting depth adjustments by changing the vertical angle at which the handle tube  52  is held. The handle tube  52  preferably has length adjustability (not shown), using known means such as bolts or spring-loaded pins in selectable holes.  
         [0052]     Artistic patterns often require parallel lines, as in for example concentric circles and checkerboard patterns. A laterally extendable guide tube  46  may be provided to visually guide the user in cutting parallel lines. The guide tube has a length adjustment  50 . For example the guide tube may comprise telescoping nested tubes locked with a threaded collet sleeve  50  or other known means. The user sets the length of the guide tube to a desired distance between parallel cuts. Then the user pushes the machine beside a previous cut while visually maintaining the distal end of the guide tube over the previous cut. A rubber band may be provided on the proximal segment of the guide tube to provide a distance indication when it is shorter than the proximal segment of the tube. The guide tube is mounted by a pivot attachment  48  on a distal end of a wheel axle or on another stationary part. It has a pivot stop that holds the guide tube approximately horizontal, but allows it to be folded upward or against the handle tube when not in use.  
         [0053]     Although the present invention has been described herein with respect to preferred embodiments, it will be understood that the foregoing description is intended to be illustrative, not restrictive. Modifications of the present invention will occur to those skilled in the art. All such modifications that fall within the scope of the appended claims are intended to be within the scope and spirit of the present invention.