Abstract:
An improved feedout mechanism for the cutting head of a rotary trimmer includes curved surfaces on the top of the lower row of the cam tangs which replace the original flat surfaces of the lower row of cam tangs in the prior art cutting head. Also, the lower surface of each follower tang also has a curved surface which is changed from the original flat design in the prior art. The curved surfaces of the follower tangs and the cam tangs facilitate the line advancement operation and prevents the follower tangs from being hung up with the cam tangs.

Description:
[0001]    This application claims priority to an application entitled “ROTARY TRIMMER HEAD WITH ADVANCING SYSTEM HAVING ROUNDED TANGS” filed in the United States Patent and Trademark Office on Jan. 17, 2007 and assigned Ser. No. 60/880,874, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The subject invention relates generally to cutting heads for rotary trimmers. More specifically, it relates to an improved cutting head for rotary trimmers using monofilament string as a means for cutting vegetation. The subject invention represents an improvement over existing designs as it allows a smoother feedout of the monofilament string as required by the operator of the trimmer and smoother operation of the trimmer head. The subject invention is an improvement over the invention of U.S. Pat. No. 6,735,874 B2 which issued on May 18, 2004 and is assigned to the assignee of the subject application. 
         [0004]    2. Description of the Prior Art 
         [0005]    Cutting heads for rotary trimmers are well known in the art and have been the subject of previous United States patents. Most relevant to the subject invention are U.S. Pat. Nos. 4,259,782; 4,458,419; 4,097,991 and 4,959,904 which issued to Proulx, the disclosures of which are incorporated herein by reference. Most relevant to the subject invention is applicant&#39;s U.S. Pat. No. 6,735,874 B2 which is referred to above. 
         [0006]    The Proulx patents disclose a flail feedout mechanism for a rotary trimmer that comprises a spinning housing that contains a spool of filament, a plurality of orifices for extending the filaments outwardly into the cutting position and a means that normally restricts movement between the spool and the housing, or can be released at a predetermined rotational distance so that additional filament length can be fed out of the orifice. The means is generally referred to as an advancing mechanism in the art. 
         [0007]    Proulx&#39;s advancing mechanism for restricting filament feedout includes, as part of the spool, a downwardly projecting bumper that normally spaces the exposed filament above the surface being cut. The spool, bumper, and an intermediate member, as an assembly, are spring loaded downwardly with respect to the spinning housing. A plurality of tangs extend inwardly from the intermediate cylinder that rides in a serpentinous cam slot in a cam member fixed to the housing. When the bumper is bumped on the ground, the intermediate cylinder is moved upwardly so that its tangs ride up relatively vertical cam surfaces until they reach spiral surfaces that extend downwardly to the next vertical cam surfaces. The net effect is that the spool, connected to the cam member, rotates relative to each other to allow a predetermined length of filament string to feed out by centrifugal force. Since a serpentinous cam is used, a single bump feeds out a single segment of filament. 
         [0008]    However, the Proulx designs are flawed in that the feedout mechanism does not operate smoothly resulting in erratic and jerky operation. In addition, the tangs on certain advancing mechanisms of the Proulx designs are subject to breakage, thereby compromising the structural integrity of the Proulx designs. The erratic and jerky operation of the Proulx designs is uncomfortable for the user and can potentially cause the filament to feedout unevenly or even jam. 
         [0009]    The shortcomings of the Proulx designs are overcome by applicant&#39;s invention of U.S. Pat. No. 6,735,874 B2, the disclosure of which is incorporated herein in its entirety by reference. The cutting head of applicant&#39;s rotary trimmer of U.S. Pat. No. 6,735,874 B2 is an improvement upon the feedout mechanism of the Proulx U.S. Pat. No. 4,259,782 and employs the same basic structural architecture. In applicant&#39;s rotary trimmer, the trimmer includes a hollow handle with an attached drive means that is connected to a spring housing. The housing has a spool containing one or more coils of string used as filaments for cutting vegetation. A pair of orifices is oppositely positioned on the spool for guiding the exposed filament to the proper cutting position. 
         [0010]    The advancing mechanism of applicant&#39;s U.S. Pat. No. 6,735,874 B2 contains a follower member having a number of tangs that have a base that is wider than the rounded end to form a taper from the base to the tip. In effect, the configuration of applicant&#39;s follower tangs are of generally truncated, bell-shaped configuration. The follower member is coupled to a cam having offset tangs for controlling the amount of string feedout of the cutting head to a predetermined length. The tangs of the cam also have a base that is wider than the rounded tip to form a taper from base to tip and is also effectively of truncated, bell-shaped configuration. This configuration results in better force distribution when the tangs of the follower and the tangs of the cam engage each other, thereby causing a smoother feedout of the filament and a sturdier trimmer head. A biasing spring maintains the follower member and the cam of U.S. Pat. No. 6,735,874 properly positioned within the housing so that string is only fed out when the housing is momentarily bounced on the ground. 
         [0011]    Although the trimmer head of applicant&#39;s U.S. Pat. No. 6,735,874 B2 operates satisfactorily and is an improvement over prior existing trimmer heads, under certain conditions of speed and load, in particular, when applicant&#39;s prior trimmer head was tapped on the ground to release more line, and while the trimmer line was not contacting any vegetation, certain problems developed. On rare occasions it was possible for the follower tangs to rest on top of the flat surface of the lower row of cam tangs. At that position, the follower tangs remain stuck on the cam tangs until the trimmer head was tapped on the ground a second time. The normal force of the compression spring attempting to push the follower member downwardly over the cam member would create friction between the lower flat surface of the follower tangs and the upper flat surface of the lower row of cam tangs. This friction was sufficient to keep the follower member lightly stuck in the upward position, such that under light engine load of the trimmer, and when the trimming line was not in contact with vegetation (a condition typical at the moment when line is being advanced), the normal torsional vibration of the machine was not sufficient to shake the follower loose. As such, the follower could not return to its downward position to complete the line advancement operation. 
         [0012]    Accordingly, it is an object of the subject invention to provide a new and improved advancing system for a trimmer head which prevents the follower member from being stuck in the upward position on the cam member, as occurred occasionally in connection with the trimmer head of applicant&#39;s U.S. Pat. No. 6,735,874 B2. 
         [0013]    It is a further object of the subject invention to provide a cutting head that has a smooth feedout mechanism. 
         [0014]    It is another object of the subject invention to provide a cutting head that can be retrofitted onto existing rotary trimmers. 
         [0015]    Still a further object of the subject intention is to provide a cutting head that is simple, low-cost to manufacture, and of sturdier construction and smoother operation than prior art cutting heads. 
         [0016]    These and other objects of the subject invention will become apparent to those of skill in the art from the accompanying drawings and the following detailed description. 
       SUMMARY OF THE INVENTION 
       [0017]    The cutting head for a rotary trimmer of the subject invention is an improvement upon the feedout mechanism of U.S. Pat. No. 6,735,874 and employs the same basic structural architecture. Briefly, the advancing system of the subject invention includes curved surfaces on the top of the lower row of the cam tangs which replace the original flat surfaces of the lower row of cam tangs. These four curved cam surfaces are the only things that are changed from the cam design of U.S. Pat. No. 6,735,874 B2. The lower surface of each follower tang has also been changed from the design in applicant&#39;s U.S. Pat. No. 6,735,874 in that each lower surface of each follower tang has a curved surface which has been changed from the original flat design. 
         [0018]    Because of the curved surfaces of the follower tangs and the lower row of cam tangs in the subject invention, the downward force of the compression spring acting on these curved surfaces now forces the follower to continue rotating so that it can complete the line advancement operation and return to its downward position. Because both the lower row of cam tangs and the follower tangs are curved, it now becomes extremely unlikely, in fact nearly impossible, for the follower member to come to rest in a position that would allow it to set or stall on top of the upper surface of the lower row of curved cam tangs. 
         [0019]    Another equally important benefit of the subject invention is that the curved surfaces of the follower tangs and the lower row of cam tangs make it easier for the follower to accomplish its first few degrees of rotation immediately after the initial upward movement which initiates the line advancement operation. 
         [0020]    Another benefit achieved by the subject invention is that the new curved design of both the lower row of the cam tangs and the follower member results in plastic having been removed from the lower corners of the follower tangs and from the upper corners of the lower row of cam tangs. This removal of plastic was required in order to convert the previously flat surfaces into curved surfaces. This removal of plastic from where it used to be has created additional clearance space in the advancing mechanism, greatly improving its freedom of movement, and with almost no sacrifice in the strength of the follower tangs and lower row of cam tangs. It should be noted, as shown in the drawings of the subject invention, that the respective curved surfaces of the follower tangs and the cam tangs are dome shaped to facilitate the smooth operation of the subject invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is an exploded perspective view of the prior art flail feedout assembly of U.S. Pat. No. 6,735,874 B2; 
           [0022]      FIG. 2  is a exploded perspective view of the new and improved follower and cam members of the subject invention; 
           [0023]      FIG. 3  is a side elevational view of the cam assembly of  FIG. 2  as viewed along line  3 - 3  in  FIG. 2 ; 
           [0024]      FIG. 4  is a cross-sectional view of the follower member of  FIG. 2  taken along line  44  of  FIG. 2 ; 
           [0025]      FIG. 5  is another exploded perspective view of the follower and cam members of the subject invention, taken from the bottom side thereof; 
           [0026]      FIG. 6  is a perspective view of the follower and cam assemblies of the subject invention in the normal driving (downward) position; 
           [0027]      FIG. 7  is a perspective view of the follower and cam members of the subject invention at the midpoint of advancing (upward) position; 
           [0028]      FIG. 8  is a perspective view, partially in section, of the follower and cam members in the advanced (upward) position, as in  FIG. 7 ; and 
           [0029]      FIG. 9  is a side elevational view, partially in section, taken along line  9 - 9  in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]    Turning to  FIG. 1 , there is illustrated the flail feedout mechanism or assembly according to applicant&#39;s prior invention of U.S. Pat. No. 6,735,874 B2. The prior art flail feedout mechanism assembly  300 , as illustrated in  FIG. 1 , basically comprises a follower member  302 , a cam member  304 , and a spool member  306 . The follower member  302  is of generally cylindrical configuration having four uniformly spaced tangs  308  adjacent to the upper surface  310  of the follower member  302 . Projecting radially outwardly of the follower member  302 , and uniformly spaced, are six knobs, each designated by the numeral  312 . 
         [0031]    As noted in the detailed description of U.S. Pat. No. 6,735,874 B2, the upper and lower surfaces of each tang  308  is planar. 
         [0032]    Cam member  304  has a lower, annular plate  320  of a diameter slightly less than the inner diameter of the cylindrical follower member  302 . Formed integral with the plate  320 , and formed adjacent the upper surface of the cam member  304 , is a serpentinous cam groove  324 . The cam groove  324  has radially oriented lower surfaces  326 ,  328  and a lower row of tangs  330 . The upper surface  332  of the cam groove  324  is formed by an upper row of tangs  334 . 
         [0033]    The spool member  306  includes six grooves  350 ,  352  in its inner cylindrical surface  354 . The grooves  350  are diametrically opposed and axially aligned within the spool member  306  and extend from the top surface  354  of the spool member  306  down to a radially oriented abutment surface  356  having lateral cutouts  358  adjacent thereto. The grooves  350  receive two outwardly extending, diametrically opposed knobs  312  which slide therealong and lock the follower member  302  to which the knobs  312  are mounted to rotate with the spool member  306 . The grooves  352  also extend from the top surface  354  of the spool member  306  down to the radially oriented abutment surface  356 , with the width of each groove  354  corresponding to the maximum width of the grooves  350 , including the lateral cutouts  358 . Accordingly, in the locked position of the follower member  302  in the spool member  306 , each of the six knobs  312  bears against a sidewall of the respective grooves  350 ,  352 , thereby providing enhanced structural contact between the follower member  302  and the spool member  306  so as to improve the efficiency and smoothness of operation of the flail feedout assembly  300 . 
         [0034]    As described in U.S. Pat. No. 6,735,874 B2, the upper surfaces of the lower row of tangs  330  are flat or generally planar. 
         [0035]    As noted above, with the design as shown in FIG. 1 of U.S. Pat. No. 6,735,874 B2, it is possible, under certain conditions of speed and load, that the flat surfaces of the lower row of tangs  330  and the flat surfaces of the follower tangs  308 , under the action of a compression spring, may cause the follower member to be lightly stuck in the upward position and, thus, interfere with the advancing of the trimmer line out of the trimmer head. 
         [0036]    In order to obviate the above-mentioned possible problem, the subject invention, as illustrated in  FIGS. 2-9 , provides that the upper surfaces of the lower row of cam tangs  330 ′ and the lower surfaces of the follower tangs  308 ′ have curved or domed surfaces, as contrasted to the planar surfaces in the prior art. As illustrated in  FIG. 2 , the cam member  304 ′ has radially outwardly oriented tangs  330 ′ which include upper curved surfaces  331 ′. 
         [0037]    The upper curved or domed surfaces  331 ′ of the lower row of cam tangs  330 ′ is illustrated in  FIG. 3  which is a side elevational view of the cam  304 ′. Each upper curved surface preferably includes two downwardly inclined surfaces disposed at approximately a 60° angle to the vertical axis. The inclined surfaces meet at the apex which is rounded, preferably at a radius of 0.125 inches, as illustrated in  FIG. 3 . Note that the upper tangs  334 ′ of the cam member include planar upper and lower surfaces designated by the numerals  335 ′ and 336′. 
         [0038]    Turning to  FIG. 4 , the lower surface  309 ′ of each follower tang  308 ′ of the follower member  302 ′ is also curved or domed. Preferably the entire lower bearing surface of each follower tang is arcuate, at a radius of approximately 0.256 inches, as illustrated in  FIG. 4 . 
         [0039]      FIG. 5  illustrates the follower and cam members as viewed from the bottom side thereof. 
         [0040]      FIG. 6  illustrates the normal driving position of the advancing assembly of the subject invention, wherein the lower tangs  330 ′ of the cam member  304 ′ are engaged with the sidewalls of the upper tangs  308 ′ of the follower member  302 ′. 
         [0041]    Turning to  FIGS. 7 ,  8  and  9 , in  FIG. 7  there is illustrated the midpoint of the advancing system of the subject invention wherein the follower is in the upward position. At such time, the lower curved surfaces  309 ′ of the follower tangs  308 ′ are in engagement with the curved upper surfaces  331 ′ of the lower row of tangs  330 ′ of the cam  304 ′. At that point, the respective curved tangs, in engagement, are actually in line engagement and, thus, there is slight chance that the respective members would be stuck in the upward position and hinder the advancement of the flail. 
         [0042]    With the follower member in the upward position as illustrated in  FIGS. 7-9 , there is additional compression on the spring which is normally pushing lightly downward on the follower member  302 ′. Because of the curvature on the lower surface of the follower tang  308 ′ and the curvature on the upper surface  335 ′ of the lower row of cam tangs  330 ′, it becomes nearly impossible for the follower to become stuck in the upward position, as was the occasion in the prior art design when these surfaces were flat and perpendicular to the vertical axis. 
         [0043]    Because of the curved surfaces in the subject invention, as particularly depicted in  FIG. 9 , the downward force of the compression spring acting on these curved surfaces now forces the follower to continue rotating so it can complete the flail line advancement operation and return to its downward position. 
         [0044]    Because both the lower row of the cam tangs and the follower tangs are curved as described above, it now becomes extremely unlikely for the follower member to come to rest in a position that would allow the follower member to set on top of the upper surface of the lower curved row of cam tangs. It is still theoretically possible, even with the subject design, that the follower tangs could come to rest on top of the cam tangs if the two curved surfaces were exactly centered, with one above the other as shown in  FIG. 9 . However, in actual practice, this does not occur since now, even the tiniest amount of torsional vibration caused by the engine, which is always present in the trimmer machine, can sufficiently bump the angular position of the follower member relative to the cam member such that the two curved surfaces are no longer in line contact and exactly centered one above the other. Once these two surfaces are no longer in line contact, they act as ramps allowing the downward force of the compression spring to force the follower to continue its rotation until the follower tangs have completely slid off the top of the lower row of cam tangs to the position as illustrated in  FIG. 6 . 
         [0045]    Another equally important benefit of the subject invention is that the curved surfaces make it easier for the follower to accomplish its first few degrees of rotation immediately after the initial upward movement which initiates the flail line advancement operation. In other words, the follower tangs now make the transition up and on top of the lower row of the cam tangs much easier than before. This is because, in the subject invention, plastic has been removed from the lower corners of the follower tangs and from the upper corners of the lower row of cam tangs, in order to convert the prior art flat surfaces into curved surfaces. This removal of plastic from where it used to be has created additional clearance space for the mechanism, greatly improving its freedom of movement and with almost no sacrifice in the strength of the tangs. 
         [0046]    It should also be noted that the design changes of the subject invention were accomplished with only a slight modification to existing tooling, and the cost of manufacture is practically unchanged. Indeed, less plastic is used, and there is a possible small savings because of that factor. 
         [0047]    Thus, there has been shown and described an improved automatic flail feedout mechanism which fulfils all of the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering the foregoing specification together with the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention.