Abstract:
A mower having a mowing head with a stationary horizontal comb and a continuous cutting blade loop slidingly positioned against the bottom surface of the comb, both having teeth arranged to accept and then shear off plant material between them at a user defined height above the ground. The teeth in the continuous cutting blade loop move past the teeth in the comb, powered by one or more drive guide pulleys transferring motive power to the blade from an external source, are mounted.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention pertains to the field of mowers. More particularly, the invention pertains to a mower having a continuous cutting blade loop. 
         [0003]    2. Description of Related Art 
         [0004]    Lawn mowers have been in production and use since the early part of the 19 th  century, and have been developed in three distinct basic configurations: reel mowers, rotary mowers, and sickle bar mowers. The advantages and drawbacks of the three configurations are described herein. 
         [0005]    The first reel mower was designed in 1827 by Edwin Budding and granted a British Patent in 1830, and a later US Patent to Passmore (1879, Reissue Number 8,560). The fundamental reel mower concept concept, one that is still in use today, relied on three major components: a cutting cylinder or reel, a stationary bed knife, and a frame upon which all cutting components and carriage could be mounted. The cutting cylinder, or reel, comprised a multitude of helical knifes arranged to form an open cutting cylinder. The cutting cylinder in turn was mounted on a longitudinal axle that received motive force from the carriage wheels when the mower was pushed, causing it to rotate. At the lower side of the cutting cylinder, a stationary bed knife was positioned to be in close proximity to the rotating helical knives such that plant material would be swept into the cutting cylinder as it rotated and the mower moved forward, and then sheared between the rotating helical knives and the stationary bed knife. Gearing between the carriage wheels, whether through actual gears or by means of a drive chain connection, ensured that the cutting cylinder would rotate at sufficiently high RPM when the mower was pushed by human power along the cutting pathway. Since that time, this basic configuration has been embodied in many forms ranging from push mowers for domestic use, to large ganged sets of mowers towed behind tractors for large mowing operations, e.g., golf course fairways. 
         [0006]    Reel mowers are characterized by a clean uniform shearing cut at the height of the bed knife which is advantageous for the health and recovery of the plant material being cut. While this arrangement is well suited to human powered configurations and has been adapted to self powered systems using internal combustion engines, maintenance of the mower by the user is cumbersome. The helical blades of the cutting cylinder are not removable and require special tooling to be sharpened, and the stationary bed knife must be removed for sharpening and replaced with proper tolerances between its cutting edge and the pathway of the rotating cylinder helical knives for optimal operation. 
         [0007]    Rotary mowers were first introduced in the 1920&#39;s. In this configuration a planer knife is positioned in the horizontal plane and rotated via a vertical shaft through its center of mass, being sharpened on the leading edge of this rotation on each end for at least part of its length. As the knife rotates about its axis, the sharpened ends impact the plant material being cut, and cuts it off. The cuts produced by rotary mowers tend to be less uniform than those of reel mowers, also resulting in more trauma to the plant material. 
         [0008]    Due to their high rotational speed, rotary mowers are also enclosed in decks that serve as a mounting frame with a shroud extending downward around the cutting knife for safety, the clippings being either mulched by the rotating blade, or expelled at high speed through a port in the protective shroud. Rotary configurations, while extremely popular, have some drawbacks in addition to the less preferred cutting characteristics previously mentioned. 
         [0009]    As the cutting blade is primarily surrounded by a safety shroud, rotary motors are not well suited for cutting long grass or weeds in general, as the portion of the safety shroud in the direction of the cutting pathway impacts tall plant material causing resistance to forward movement. Further, the containment of the cuttings under the deck by the shroud can cause the rotary knife to bog down in extreme examples, slowing to a point of not being able to effectively cut, or stopping. More recently, high torque electric motors have been added to provide motive force to the rotating blade, but must rely on lengthy cords for electrical power, or batteries with relatively limited lifetime and long charge periods in between. Removal of the blade on rotary mowers for sharpening is also a relatively involved process requiring tools. 
         [0010]    The third category is the sickle bar mower. A stationary sickle bar, or comb, having teeth extending radially from its leading edge and separated by a gap between adjacent teeth, directs plant material against the back of each gap. An oscillating cutting bar, slidingly positioned in contact with the lower surface of the stationary comb, also has mating teeth in its leading edge that alternatively cause the gap between the comb teeth to open, allowing plant material to enter the gap, then close laterally, causing a shearing action at the edge of the stationary teeth and oscillating teeth, thus cutting the plant material. Sickle bar mowers have found primary applications in agricultural use as their shear cut on plant material has advantages similar to those produced with reel mowers, and they can be constructed to be mounted in various positions such as at the front of a tractor, or as outriggers for mowing difficult regions around ditches or embankments when the sickle bar is raised or lowered at some angle relative to the horizontal. Further, because of free access above and in front of the sickle bar, they are well suited to mowing tall plants and even light brush, with the clippings falling uniformly behind the sickle bar. 
         [0011]    However, sickle bar mowers have been limited to receiving motive force from internal combustion sources as the reciprocal nature of the cutting blade requires translation of rotational motion (from an engine or motor shaft, or tractor power take-off unit) into reciprocating motion of the blade. Such a translation is inefficient as it requires the blade to decelerate, stop, and accelerate in the opposite direction during each reciprocating cycle. As such they have been difficult to implement in a human powered form for domestic lawn maintenance. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention integrates advantageous shearing cut characteristics in a mowing head that also provides efficient motive power requirements and ease of blade replacement. The mowing head of the mower has a stationary horizontal comb and a continuous cutting blade loop slidingly positioned against the bottom surface of the comb, both having teeth arranged to accept and then shear off plant material between them at a user defined height above the ground. The teeth in the continuous cutting blade loop move past the teeth in the comb, powered by one or more drive guide pulleys transferring motive power to the blade from an external source, are mounted. 
         [0013]    A cutting apparatus is discussed below that is advantageous to the health of plant material being cut, as well as an energy efficient mechanical system that is suited to human power by taking motive force from the wheels of a carriage being pushed by a human. Alternatively, the sickle bar mowing head may efficiently receive drive guide pulley motive force from a small electric motor or internal combustion engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0014]      FIG. 1  shows a schematic of one exemplary embodiment of the sickle bar mower head using a walk-behind human powered carriage. 
           [0015]      FIG. 2  shows a schematic of one exemplary embodiment of the sickle bar mower head used with a walk-behind human powered carriage. 
           [0016]      FIG. 3A  shows a detailed perspective view of one exemplary embodiment of the sickle bar mower head incorporating a continuous cutting blade loop, blade tensioner, and comb. 
           [0017]      FIG. 3B  shows a frontal view of one exemplary embodiment of the sickle bar mower head in which an additional free wheel guide pulley is used in conjunction with a blade tensioner spring. 
           [0018]      FIG. 3C  shows a side view of a free wheel guide pulley incorporating both a tensioner spring and a tracking adjustment that allows the angle of the free wheel guide pulley axle to be changed relative to the plane of the chassis. 
           [0019]      FIG. 4A  shows the generalized comb-blade combination and comb-blade tooth spacing relationship. 
           [0020]      FIG. 4B  shows a profile cut through a two piece comb having an upper half and a lower half machined to form a slot for the continuous cutting blade loop. 
           [0021]      FIG. 4C  shows a profile cut through of a one piece comb having retaining wheels at its trailing edge to hold the continuous cutting blade loop against the lower surface of the comb and prevent rearward movement of the continuous cutting blade loop. 
           [0022]      FIG. 4D  shows one exemplary embodiment of the blade tensioner used in conjunction with a comb that is curved. 
           [0023]      FIG. 5  shows one exemplary embodiment of a blade tensioner having a tensioner pulley, a tensioner arm, and tensioner spring. 
           [0024]      FIG. 6  shows one exemplary embodiment of gear drive transferring rotary motion from the carriage wheel of a human powered carriage to a drive guide pulley. 
           [0025]      FIG. 7  shows a mounting of the mower head with a carriage wheel allowing cutting height adjustment of the mower head. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIGS. 1-2  show an embodiment of the present invention, with a mowing head  10 , a chassis  20 , a continuous cutting blade loop  30 , at least one drive guide pulley  40 , at least one free wheel guide pulley  50 , a blade tensioner  60 , and comb  70 . In this embodiment, the chassis  20  of mower head  10  is mounted to a push-type carriage  80  having two main wheels  90  and a third trailing support wheel  100 , coupled to a carriage frame  110 . While a three wheel carriage is depicted, this embodiment is in no way intended to limit the invention, as a variety of carriage systems could be employed including a two- or four-wheel push-type system, a self-propelled carriage using either an electric motor or internal combustion engine, or an adaptor for mounting to the bucket of a front end loader or to a three-point hitch and power takeoff on a standard farm or garden tractor, or under the frame of a garden tractor or small utility tractor. It could also be configured on an arm extending outward to the side of a tractor, as in conventional sickle-bar mowers. Multiple mower heads  10  may also be ganged in groups for large area mowing when towed in groups behind a tractor or small utility vehicle. 
         [0027]      FIG. 3A  shows the mowing head  10  in greater detail. The chassis  20  provides structural support to the mowing head  10  and mounting points for all of its components. This chassis  20  may be constructed of stamped sheet metal, cast from lightweight metal alloys or structural plastics, or welded together from individual elements to form a rigid structure. In addition to mounting points for the mower components, the chassis  20  also incorporates mounting holes and/or brackets as necessary for the intended carriage system  80 . At a minimum, the chassis  20  will include attachment points for each drive guide pulley axle  45 , for example with a through bearing  22 , and free wheel guide pulley axle  53 . 
         [0028]    Although only two guide pulleys are shown in this embodiment, other configurations are possible and may be advantageous. A third free wheel guide pulley  51  with an axle  55  and bearing  58 , as shown in  FIG. 3B-3C , may be added on the inner circumference  32  of the continuous cutting blade loop  30 . An integrated tension spring  52 , may also be present to eliminate the need for a separate dedicated tensioner  60 , and may also include a tracking adjustment  54  that changes the pitch of the free wheel guide pulley  51  to ensure the blade does not undesirably migrate toward the front or back of the pulleys  40 ,  50 , which can cause the continuous cutting blade loop  30  to slip off or bind with other structures, such as the chassis  20 , as it is fed through its transit path indicated with arrows in the  FIGS. 3A ,  3 B and  4 A The tension spring  52  and tracking adjustment  54  elements may also be added to the free wheel guide pulley  50  in lieu of adding an additional free wheel guide pulley  51 . 
         [0029]    The chassis  20  also includes mounting holes or brackets for attachment of the comb  70 . The lower surface  78  of the comb  70  is ideally coincident with lines that tangentially connect the first end of the comb  70  with the drive guide pulley  40  and the second end of the comb  70  with the free wheel guide pulley  50  at their lower circumference. In such an arrangement, the inner perimeter  32  of the continuous loop blade  30  will be positioned in sliding contact with the lower surface  78  of the comb  70 . 
         [0030]      FIG. 4A  illustrates the relation between the continuous cutting blade loop  30  and the comb  70  in more detail. The comb  70  has a series of comb teeth  120  dispersed along its leading edge, each adjacent comb tooth  120  being separated by a gap  130 . In this illustration the gaps  130  are shown as simple vertical slots with angular perimeters, and the comb teeth  120  similarly shown as simple compound angular geometries with vertical sides. It is however understood that a wide variety of curvatures may be used in defining the perimeters of the teeth  120  and gaps  130 , and that their vertical aspects through the comb  70  may include a variety of angulations ranging from a perpendicular to the lower surface  78  of the comb  70 , to an acute angle bevel profile resulting in a larger gap at the top surface  79  of the comb  70  than at the bottom surface  78  of the comb  70 . Further, the width of the comb teeth  120 , W F , and the width of the gaps  130 , W G , is subject to a wide range of dimensions depending on the type of plant material being mowed, for example finer grasses may use a narrower comb teeth  120 , W F , and narrower gaps  130 , W G , coarser brush may use a wider comb teeth  120 , W F , and broader gaps  130 , W G . 
         [0031]    The continuous cutting blade loop  30  is formed from a strip of metal, for example a bimetal made of high speed steel bonded to a high-strength carbon steel base, with a series of blade teeth  140  extending radially from its leading edge. After teeth  140  have been formed on this strip of metal, the ends of the metal strip are welded together, and the weld ground to the level of the loop on its inner perimeter  32  and outer perimeter  34  to form a single smooth continuous cutting blade loop  30 . If desired, more robust metals such as carbide, or other metals, can be applied to the continuous cutting blade loop teeth  140  for longer life and better shearing characteristics. As with the comb teeth  120  and comb gaps  130 , the continuous cutting blade loop teeth  140  in this example are shown as simple square notches cut at regular intervals. However, tooth shape, depth, width and spacing on the blade are subject to variation, and this depiction is not intended to limit the scope of the invention in this regard. Each cutting tooth  140  however has a shear edge  36  in the direction of blade travel, indicated by arrows in  FIG. 4A . The comb teeth also have a stationary shear edge  73 . As the continuous cutting blade loop  30  tooth  140  shearing edge  36  moves past the comb  70  tooth  120  shearing edge  73  plant material in the gap  130  is cut. 
         [0032]    Of particular note in  FIG. 4A , is the separation of the comb teeth  120 , D F , relative to the separation of the continuous cutting blade loop teeth  140 , D T . Having the same separation in both cases, D F =D T , results in a situation in which all comb teeth  120  are repeatedly in the same phase of shearing at the same time as the shear edge  36  of each tooth  140  of the continuous cutting blade loop  30  moves underneath the comb  70 . This situation may cause an uneven cyclic load on the external power source driving the continuous cutting blade loop  30  causing it to stall or bog down. In this case, the relative separation is selected to create a ratio of D F /D T  in the range of 0.5 to 1, thus staggering the point in the shear cycle at each comb tooth  120  as the continuous cutting blade loop  30  slides along the comb  70 . As a result, a lower, more continuous driving force is needed circulate the continuous cutting blade loop  30  through its course under the comb  70  and around the free wheel guide pulleys  50  and drive guide pulley  40 , as not all continuous cutting blade loop teeth  140  are shearing at the same time. 
         [0033]    As depicted in  FIG. 4A , the comb  70  may be constructed with a slot  75  running its entire length along its leading edge to retain the continuous cutting blade loop  30  in close proximity to the comb lower surface  78 . This may be accomplished by machining the slot to a depth approximately equal to the width of the continuous cutting blade loop  30 , and width slightly greater than the thickness of the continuous cutting blade loop  30 . 
         [0034]    Alternatively, as shown in  FIG. 4B , the comb  70  may be formed as an upper half  72  and lower half  74 , one or both halves being machined to form a slot  75  of appropriate dimensions when the two halves  72 . 74  are mechanically joined with screws, bolts, or other fasteners. In yet another embodiment, as shown in  FIG. 4C , the comb may be flat along its lower surface  78 , with retaining wheels  76  at its trailing edge providing both resistance to rearward motion of the continuous cutting blade loop  30 , and upward force to maintain the continuous cutting blade loop  30  in contact with the lower surface  78  of the comb  70 . 
         [0035]    In another embodiment, as shown in  FIG. 4D , the comb  70  may have a convex curved profile from its first end to its second end, thus forcing the continuous cutting blade loop  30  against its lower surface  78  at all points, with wear between the lower surface  78  of the comb  70  and the continuous cutting blade loop  30  inner circumference  32  resulting in a self sharpening action on their respective shearing edges  73 ,  36 . 
         [0036]    To facilitate easy removal, the continuous loop blade  30  is constructed to be slightly longer than the pathway it traverses around the free wheel guide pulley  50 , drive guide pulley  40 , and comb  70 . The slack created due to the additional length is adjusted by a spring loaded tensioner  60  and tensioner pulley  150 . The tensioner  60  is fitted with a spring  160  that forces the tensioner pulley  150  in rotational contact with the continuous cutting blade loop  30 , removing slack and providing sufficient frictional force between the continuous cutting blade loop  30  inner diameter  32  and drive guide pulley  40  to move the continuous cutting blade loop  30  throughout its travel path on the mowing head  10  without slippage during cutting operations. 
         [0037]    In the embodiment shown in  FIG. 5 , the tensioner wheel  150  is attached to a tensioner  60  having a spring mechanism  160 , thus applying pressure to the outer perimeter  34  of the continuous cutting blade loop  30 . However, it is understood that a variety of tensioners  60  are possible. One configuration includes a tensioner  60  and tensioner wheel  150  on the inner perimeter  32  of the continuous cutting blade loop  30 , pressing outward from its travel pathway. Also, as previously shown in  FIG. 3B , an additional free wheel guide pulley  51  may be configured with an axle  55  slidably mounted on the chassis  20  with a linear spring  52  forcing the free wheel guide pulley  51  to the outside of the continuous cutting blade loop  30  travel path. 
         [0038]    Referring now to  FIG. 6 , motive power can be provided to the axel  45  of the drive guide pulley  40  through a gear system  170  connected to one of the carriage wheels  90 . A bevel gear  190  is attached to the hub of the carriage wheel  90  in one plane, and a miter gear  180  is attached to the axle  45  of the drive guide pulley  40  in an orthogonal plane. Thus, when the carriage  80  is pushed forward, rotary motion of the wheel  90  is transferred to the drive guide pulley  40 , causing the continuous cutting blade loop  30  to move in continuous sliding contact in one direction along the lower surface  78  of the comb  70 . 
         [0039]    In this embodiment, bevel gear  190  is connected to the carriage wheel  90  using a ratchet mechanism, or one-way bearing system known in the art, to only cause the carriage wheel  90  to drive the bevel gear  190  when the carriage  80  is in forward motion. Alternatively, the bevel  190  gear may be fixed to the carriage wheel  90 , and a ratchet or one way bearing integrated in the miter gear  180  attachment to the drive guide pulley axle  45 . In this manner the angular momentum of the drive and guide pulleys can be allowed to carry the continuous cutting blade loop  30  in its direction of motion when the carriage  80  is pulled backward, or when carriage  80  forward motion is not present. To enhance this effect, a massive flywheel  56 , as shown in  FIG. 3C , may be added to one or more of the drive guide pulleys  40  and/or one or more of the free wheel guide pulleys  50 . 
         [0040]    In an alternative embodiment, motive power to the drive guide pulley  40  may be provided by an electric motor, or internal combustion engine, either directly coupled to the drive guide pulley axle  45 , or mechanically coupled through a gearing system, belt drive, or chain drive connected to its axle  45 . 
         [0041]    Referring now to  FIG. 7 , to facilitate adjustments for various cutting heights, the mower head  10  may connected to the carriage  80  using a mount  200 . The mount is constructed to pivot about the same axis of rotation as the carriage wheel  90 , and the bevel gear  190 . As a result, the orientation of the drive guide pulley  40  axle  45  is always along a radius extending from that axis, so that operational contact is maintained between the bevel gear  190  and the miter gear  180  regardless of the position of the mount  200 . This configuration makes it possible to raise the mower head  10  to various positions above the ground, for example from H 1  to H 2 , without losing power delivered from the carriage wheel  190 . 
         [0042]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.