Abstract:
A dual blade assembly for a lawn edger, the assembly comprising first ( 140 ) and second ( 142 ) generally rectangular blades arranged in a substantially cross shaped configuration for rotation about a substantially central axis (R). Each of the first ( 140 ) and second ( 142 ) blades having a central region between two end cutting regions, at least one protuberance ( 144 ) in the central region and at least one recess ( 148 ) in the central region. The promuberance(s) ( 144 ) of one of the first ( 140 ) and second ( 142 ) blades is adapted to engage with the recess(es) ( 148 ) of the other of the first ( 140 ) and second ( 142 ) blades to counteract relative movement between the first ( 140 ) and second blades ( 142 ) about the rotational axis (R).

Description:
This application is a CIP of U.S. patent application Ser. No. 08/864570 filed on May 28, 1997, now abandond. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to cutting blades and, in particular, to a dual blade assembly for a motorised lawn edging implement. 
     BACKGROUND OF THE INVENTION 
     The maintenance of a tidy natural outdoor landscape includes the regular edging or cutting of the growth of grass, plants and other vegetation along the edges of paths, curbs and gutters, garden plots, walls, fences, etc. Various methods have been used to perform these and similar tasks, using manual and motor-assisted equipment. The latter are tenned “edgers” and are increasing in popularity. 
     It is known for edgers to use a flat rectangular blade with at least one fixing hole in the blade. If only one hole is used, it is at the centre of the blade. Alternatively, a cutting disc with teeth disposed around its circumference is used. 
     During the edging or cutting process, and particularly with professional garden maintenance, it is desirable to minimise the overall time required to complete the task. It is also desirable to minimise the quantity of energy consumed, to increase the overall efficiency of the task. 
     It is also desirable to maximise the operator&#39;s comfort, which can be adversely affected when motor assisted equipment creates excessive movement and/or vibration, due to the inpact of the rotating blade on dirt, rocks and the like. 
     It is also desirable to minimise the storage space required by large quantities of cutting blades in the manufacturing and distribution stages of production. 
     Finally, it is desirable in some situations for an operator to have the ability to vary the width of the cut that the blade makes. 
     SUMMARY OF THE INVENTION 
     In the first aspect, the present invention discloses a dual blade assembly for a lawn edger, the assembly comprising first and second generally rectangular blades arranged in a substantially cross shaped configuration for rotation about a substantially central axis, each of the first and second blades having: a central region between two end cutting regions; at least one protuberance in the central region; and at least one recess in the central region, wherein the protuberance(s) of one of the first and second blades is adapted to engage with the recess(es) of the other of the first and second blades to counteract relative movement between the first and second blades about the rotational axis. 
     In the second aspect, the present invention discloses a dual blade assembly for a lawn edger, the assembly comprising first and second generally rectangular blades arranged in a substantially cross shaped configuration for rotation about a substantially central axis, each of the first and second blades being of substantially constant thickness prior to any deformation and having a central region between two end cutting regions, at least one of the first or second blades being deformed by having its end regions displaced axially from its central region, the axial distance between the opposed outermost surfaces of each of the first and second blades defining a cutting width, and wherein the first and second blades are arranged with the displaced end regions being disposed axially inwardly such that the cutting width of the blade assembly is less than or equal to twice the blade thickness of the first and second blade. 
     In the third aspect, the present invention discloses a dual blade assembly for a lawn edger, the assembly comprising: 
     first and second generally rectangular blades arranged in a substantially cross-shaped configuration for rotation about a substantially central axis, each of the first and second blades being of substantially constant thickness prior to any deformation and having a central region between two end cutting regions; and 
     means for maintaining said first and second blades in a fixed rotational relationship with respect to each other, said means comprising at least one of the first and second blades being deformed by having its end regions displaced axially from its central region forming a central deformation shaped to receive the other of the first and second blades, 
     wherein the axial distance between the opposed outermost surfaces of terminal cutting edges of the end regions of the first and second blades defines a cutting width and the first and second blades are arranged with the displaced end regions being disposed axially inwardly such that the cutting width as defined by the terminal cutting edges of the end regions of the first and second blades is less than or equal to twice the blade thickness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A number of embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, wherein; 
     FIG. 1 is a perspective view of a dual blade assembly in accordance with a first embodiment; 
     FIG. 2 is an inverted perspective view of Be dual blade assembly of FIG. 1; 
     FIG. 3 is a schematic sectional side view of the dual blade assembly of FIG. 1 along the line I—I of FIG. 1, together with a fastener to demonstrate the attachment to a lawn trimming implement; 
     FIG. 4 is a perspective view, similar to FIG. 1, of a dual blade assembly in accordance with a second embodiment; 
     FIG. 5 is a schematic sectional view of the dual blade assembly of FIG. 4 together with a fastener to demonstrate the attachment to a lawn edging implement he hatched blade shown is as viewed along the line II—II of FIG. 4, whilst the non-hatched blade shown is as viewed along the line III—III of FIG. 4; 
     FIG. 6 is a sectional side view of a dual blade assembly in accordance with a third embodiment; 
     FIG. 7 is a sectional view, similar to that of FIG. 3, of a dual blade assembly, in accordance with a fourth embodiment; 
     FIG. 8 is a sectional view, similar to that of FIG. 6, of a dual blade assembly in accordance with a fifth embodiment; 
     FIG. 9 is a side view of he fifth embodiment of FIG. 8; 
     FIG. 10 is a plan view of a dual blade assembly in accordance with a sixth embodiment; 
     FIG. 11 is a sectional view of he dual blade assembly of FIG. 10 along the line XI—XI of FIG. 10; 
     FIG. 12 is a sectional side view, similar to FIG. 10, of a dual blade assembly in accordance with a seventh embodiment; 
     FIG. 13 is a plan view of a dual blade assembly in accordance with a eighth embodiment; 
     FIG. 14 is a partial sectional side view of a dual blade assembly in accordance with a ninth embodiment; 
     FIG. 15 is a perspective view of a lawn edging implement, together with the dual blade assembly of FIG. 1 attached; 
     FIG. 16 is a sectional view of a plurality of blades in accordance with an embodiment of the present invention stacked together in storage; 
     FIG. 17 is a schematic sectional side view, similar to FIG. 10, of an arrangement of a dual blade assembly; 
     FIG. 18 is an exploded perspective view of a dual blade assembly in accordance with a tenth embodiment; 
     FIG. 19 is an assembled perspective view of the tenth embodiment of FIG. 18; 
     FIG. 20 is a cross sectional side view of the tenth embodiment of FIGS. 18 and 19; 
     FIG. 21 is an exploded perspective view of a dual blade assembly in accordance with an eleventh embodiment; 
     FIG. 22 is an assembled perspective view of the eleventh embodiment of FIG. 21; and 
     FIG. 23 is a cross sectional side view of the eleventh embodiment shown in FIGS.  21  and  22 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 to  3 , there is shown a first embodiment of a dual blade assembly  10  having a first blade  12  and a second blade  14 . The first blade  12  is a flat rectangular plate typically having a blade thickness t b  (FIG. 3) of approximately 2 mm (although the invention is not limited thereto), preferably manufactured of hardened spring steel with a fixing hole  16  provided centrally about a rotational axis R. The second blade  14  is substantially identical in overall length and thickness to the first blade  12 . However, the second blade  14  has central deformation  18  shaped to receive the first blade  12 . In this first embodiment, the central deformation  18  is such that it axially displaces upper surface  24  of the end or cutting regions of the second blade  14  by approximately 2 mm (i.e. by substantially the same thickness as for the first blade  12 ). 
     This results in the upper surface  20  of the first blade  12  being level with, or substntially level with, upper surface  24  of the second blade  14  and giving the assembly a cutting width or thickness t c  (FIG. 3) of approximately 2 mm (i.e. approximately equal to the blade thickness t b ). 
     In this embodiment, the dimension of the central deformation  18  along the length of the second blade  14  is substantially equal to the width of the first blade  12 . The central deformation  18  is also characterised by substantially right angled bend regions  26 . 
     As shown in FIG. 2, the second blade  14  also has a fixing hole  28  provided centrally about the axis R, so that when the first blade  12  and the second blade  14  are assembled as shown, the fixing holes  16  and  28  align to receive a common fixing device. When attached to a lawn edging implement, tips  30  and  32  of the blades  12  and  14  respectively, strike the grass when in use. The blades  12 ,  14  wear from each of the tips  30 ,  32  back towards the frog holes  16  and  28 . 
     The shaded areas A, B, C &amp; D indicate the material that usually wears away. This can be contrasted with the wearing away of a (higher cost) disc blade having a larger surface area and thus more steel, where he perimeter teeth wear and become blunt. The disc blade as a whole is then ineffective and the remaining steel of the disc is unable to assist in the intended cutting operation. 
     The blade arrangement provides a desirable result whereby a multi-edged, flat plane, cutting blade (in the effective cutting area) with at least four cutting edges is provided, at a lower cost of manufacture than a cutting disc with teeth disposed around its circumference, and a longer life than a cutting disc with teeth. 
     The central deformation  18  locates about the blade  12  to act as a torque resisting means and counteract any relative rotational movement of the blades  12  and  14  about the axis R. Thus in operation the blades  12 ,  14  maintain their illustrated substantially perpendicular relationship. 
     As illustrated in FIG. 3, the dual blade assembly  10 , is detachably mounted to an edging implement&#39;s horizontal shaft  34  using a fastener  36 , for example a nut, which threadably engages the shaft  34 . The first blade  12  in FIG. 3 is at the outer position on the shaft  34 . However, this arrangement can also be reversed, so that the second blade  14  is in the outer position on the shaft  34 . 
     Referring to FIG. 4, there is shown a second embodiment of a dual blade assembly  37  in which the first blade  12  is replaced with a blade  38 , which is substantially identical to second blade  14 . Therefore, the dual blade assembly  37  comprises two substantially identical blades  14  and  38 , each of which has a central deformation  18 , shaped to receive the respective blade. Each of the central deformations  18  displaces the respective blade surfaces  20  and  24  by the blade thickness t b  (approximately 2 mm). 
     FIG. 5 is a composite cross-sectional view of the dual blade assembly of FIG. 4 attached to a shaft  34 , Each blade  14 ,  38  is illustrated along the corresponding cross-sectional line II—II and III—III respectively, in order to demonstrate the relative positioning of each blade  14  and  38 . This results in a cutting width t c  into the grass which is approximately twice the blade thickness t b  of the individual blades (approximately 4 mm). As a result, there is a strip approximately 4 mm wide extending from the edge of a concrete path (for example) within which there is no vegetation. This result is sometimes preferred by some operators since the grass takes a longer period to grow back over the wider edging cut. 
     FIG. 6 similarly illustrates a third embodiment which is a variation of the second embodiment of FIG. 5, again using substantially similar blades  14  and  38 , but in which the right angled bend regions  26  adjacent the central deformations  18  have been replaced by smoother bend regions  40  of a shallow angle. This reduces the likelihood of stress concentration in the blades  14  and  38 . 
     FIG. 7 shows a fourth embodiment using the shallow bend regions  40  of the third embodiment on the blade  14  in conjunction with the flat blade  12  of the first embodiment. In this embodiment, the cutting width t c  substantially equals the blade thickness t b  (approximately 2 mm). 
     FIGS. 8 and 9 shows a fifth embodiment in which blades  42  and  44  each utilise shallow bends  40  to displace the central deformations  18  from their respective and regions  20  by approximately half the blade thickness t b  (i.e. by approximately 1 mm). 
     When this embodiment is assembled, as shown, the cutting width t c  substantially equals the blade thickness t b  (approximately 2 mm). 
     FIGS. 10 illustrates in plan view a sixth embodiment of a dual blade assembly  46 , similar to that shown in FIG. 1, but which has improved blade torque resisting properties. A first blade  48  and a second blade  50  are provided. The central deformation  18  along the length of second blade  50  is significantly wider than the width of the first blade  48 . A torque resisting arrangement for the two blades  48  and  50 , is provided on the second blade  50  by at least two, but preferably four, tangs  52 ,  54 ,  56  and  58 , pushed up from the surface of the central deformation  18 . 
     FIG. 11 illustrates the arrangement of FIG. 10 when viewed along the line XI—XI of FIG.  10  and shows how the tangs  54  and  56  are uplifted relative to the surface of the central deformation  18 . 
     FIG. 12 illustrates (in the same manner as FIG. 11) a seventh embodiment generally similar to that of FIGS. 10 and 11, but with a modified second blade  60  having at least two tangs  62  and  64  pushed up from the (undeformed) central surface of the second blade  60 . If both the blades  48  and  60  are each 2 mm thick, then the cutting width t c  this embodiment is approximately twice the blade thickness t b  (i.e. approximately 4 mm). Again, at least two, but preferably four, tangs, substantially spaced apart at the width of blade  48 , are provided as torque resisting abutments. 
     FIG. 13 illustrates an eighth embodiment, similar to that of FIG. 7, but having one blade  66  with a central deformation  18 , in which a flat blade  68  is positioned. This results in the outer surfaces of the blade  66  being substantially level with the corresponding surfaces of the blade  68  and results in a cutting width t c  equal to the blade thickness t b . At least one rivet  70  (and preferably four as illustrated) pass between the blades  66  and  68  to provide a torque resistance mechanism between the blades  66  and  68 . 
     FIG. 14 shows a ninth embodiment similar to that of FIG. 13 in which the blade  66  includes one or more, preferably four, holes or recesses  72 . The other blade  68  is stamped or pressed upon its outer surface  74  to deform a corresponding number of mating protuberances or spigots  76 . When the blades  66  and  68  are assembled as shown, the spigots  76  engage the holes  72  and provide a torque resisting mechanism between the blades  66  and  68 . This embodiment avoids the use and cost of rivets or other like fasteners. 
     Those of the foregoing embodiments which provide a cutting width t c  of equal to or less than twice the blade width t b , thereby provide a in and neat cutting path. Further, by reversing one or more of the blades to displace the end regions away from the other blade or blades, the cutting width t c  can be increased. 
     FIG. 15 shows one example of a lawn edging implement  120  with the dual blade assembly  10  of FIG. 1 attached thereto instead of a conventional single blade. 
     The implement  120  has a single ground engaging wheel  121 , a pair of handle bars  122  and a power unit or motor  124 . The wheel  121  has a sufficiently large diameter to enable the implement  120  to be easily rolled like a wheelbarrow including rolling over steps, rough terrain, lawn, tangled grass, garden bed peripheries, etc. 
     The motor  124  can be either an electric motor or any type of internal combustion engine. The motor  124  is positioned in front of the operator and is mounted at the head of the transmission frame  125  and is generally provided with a conventional speed dependent centrifugal clutch, and a gear box  126 . 
     Extending from the gear box  126  is a shaft  127  which carries the dual blade assembly  10  which is shielded by a guard  128  (illustrated partly cut away). The dual blade assembly  10  and shaft  127  are driven by the engine  24 . 
     The gear box  126  provides a gear reduction of nominally 3.5;1 with an engine of, say, 30 cc capacity. Because of the low gear ratio, the peripheral speed at the tips of the dual blade assembly  10  is kept low, even at engine speeds of up to 10,000 rpm. The two blades with four contact cutting edges provide less “chatter” during operation and a more even pulling action as the implement  120  causes the blade tips to engage with the grass. In this connection it will be appreciated that the blade assembly  10  rotates in the counter-clockwise direction as seen in FIG.  15 . 
     Another advantage of this is when edging against a concrete footpath, or the like, that has excessive vegetation growing over the footpath, Under these circumstances, the outer portions of the blades glance against (or rub along) the concrete edge, which enables the operator to follow the unseen concrete edge. Since one cutting edge of the blade arrangement  10  is thus always in contact with, or glancing against, the concrete edge, the blades act as a guiding mechanism. 
     A further advantage of the blades  14  of these arrangements will be apparent from FIG. 16, where the blades  14  can be neatly stacked or nested, one on top of one another to minimise the physical space used, in the distribution and storage stages of production. 
     FIG. 17 illustrates an arrangement of a “double thickness” blade assembly having a cutting width t c  equal to twice the blade thickness t b  using two flat blades  130 , each 2 mm thick. The blades  130  are fastened together with at least one fastener  132 , for example a rivet, which in conjunction with the central shaft  34 , provides a torque resisting arrangement to prevent the blades  130  from rotating relative to one another. An alternative torque resistant arrangement using the double thickness blade assembly is to use the spigot and hole arrangement of FIG.  14  and/or the tang arrangement of FIGS. 10 to  12 . 
     FIGS. 18 to  20  illustrate an arrangement of a “single thickness” blade assembly having a cutting width t c  equal the blade thickness t b  using one flat blade  140  and one deformed blade  142 , each 2 mm thick. Each of the blades  140 ,  142  include a pair of protuberances  144  formed by stamping one side of the blade material so as to displace a portion of blade material  146  (see FIG. 20) of the thickness of the blades  140 ,  142 . The stamping creates a depression on the stamped side of the blade and the raised protuberances  144 , of equal height to the depression depth, on the other side of the blade. Each of the blades  140 ,  142  also includes a pair of recesses  148  formed by punching holes in the blades  140 ,  142 . It is important to note that location and size of the protuberances  144  and recesses  148  are identical in each of the blades  140 ,  142 . 
     When the blades  140 ,  142  are assembled in a cross shaped configuration (as shown), the protuberances  144  of one of the blades engage the recesses  148  of the other blade and vice versa to provide a torque resistance mechanism between the blades  140 ,  142 . 
     FIGS. 21 and 23 illustrates an equivalent arrangement to that shown in FIGS. 18 to  20  but using two flat blades  140  to provide a “double thickness” blade assembly having a cutting width t c  equal to twice the blade thickness t b . 
     A particular advantage associated with the embodiments shown in FIGS. 18 to  20  and FIGS. 21 to  23  is that the protuberances/recesses torque resistant mechanism is identical in both blades which simplifies manufacture and, in the case of the double thickness blade assembly shown in FIGS. 21 to  23 , reduces inventory as two identical blades are used. 
     The blades  140 ,  142  also each have one central hole  152  for attachment to a lawn edger and two outer holes  150 . The three holes  150 ,  152  allow a number of blades to be bolted together in a stacked configuration (similar to that shown in FIG.  16 ), which reduces warpage during heat treatment. 
     Numerous modification and alterations, apparent to one skilled in the art, can be made to the described embodiments without departing from the spirit and scope of the present invention. For example, the central deformations can be configured to allow the blades to sit in a St Andrew&#39;s cross arrangement rather than a St George&#39;s cross as illustrated. Further, any of the above blade arrangements can also be used with a vertical (rather than horizontal) shaft for example in a vegetation brush cutter, string trimmer (i.e. a line trimmer or “WHIPPER SNIPPER” [Trade Name]), or the like. Also, any of the torque resisting arrangements described can be used in combination with any of the embodiments of the dual blade assemblies. 
     All such modifications and alterations are to be considered within the scope of the present invention, embodiments of which have been hereinbefore described.