Abstract:
A cutting head for a rotary trimmer has a rotating body from which several flexible cord-like filament cutting blades or flails extend radially so that additional flail length can be fed from the device by merely bumping the rotating body on the ground. The improvement includes a plurality of truncated, bell-shaped configured tangs which extend into a serpentinous cam slot. Bumping of the device on the ground causes the tangs to move from stable positions to other stable positions allowing relative movement between the outer case of the trimmer and a spool of flail therein so that a predetermined length of flail is fed out through the case.

Description:
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/388,155 filed Jun. 11, 2002, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention relates to cutting heads for rotary trimmers and, 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 presently existing cutter head designs and allows for a smoother, more efficient feedout of the monofilament string during operation of the cutter head. 
     2. Description of the Related Art 
     Flail feedout means for mowing and trimming devices used to trim grass, weeds, and other vegetation, of the rotary type equipped with flexible cord-like flails formed of generally cylindrical fibers, are well known in the art. Grass and weed cutters of this general type are widely known and the subject of various patented devices including those described in Ballas et al., U.S. Pat. No. 3,826,068; Mizuno et al., U.S. Pat. No. 4,020,552; Prouix, U.S. Pat. No. 4,097,991; Perdue, U.S. Pat. No. 4,134,204; Toro, Belgium Patent No. 852,150; and Prouix, U.S. Pat. No. 4,259,782. Such devices are available on the market having automatic flail feedout mechanisms which respond to a bump on the ground intentionally applied by the operator or by the application of force applied thereto by some mechanical arrangement. Such mechanisms usually consist of a dog or friction clutch located between a spool of flail and the case thereabout through which the flail is fed. By bumping an extension of the spool on the ground, the friction clutch is disengaged for a length of time dependent on the duration of the bump. The dog clutch released by the bump then abruptly engages at the next opportunity to feed out flail in segment lengths which are related to the engagement points of the dog clutch. Such dog clutches have outwardly extending ribs which engage inwardly extending abutment tangs and therefore depend upon a skillful bump when it is desired that they move only one segment. However, friction within the device and overzealous bumping can result in two or more line segments being fed out, especially when the device has been in use and the corners on the ribs and tangs have worn so that positive engagement is no longer assured. 
     An improved flail feedout mechanism for a rotary mower is disclosed in the above-mentioned U.S. Pat. No. 4,259,782, the disclosure of which is incorporated herein by reference. This prior art mower includes a handle with drive means which are connected to a spinning housing which contains a spool of one or more coils of filaments used as flails, an orifice through the housing for each coil for extending the flail outwardly into cutting position, and means which normally restrict movement between the spool and the housing but can be released a predetermined rotational distance so that additional flail can be fed out of the orifice. These last-mentioned means include, as part of the spool, a downwardly projecting bumper which is normally used to space the flail above the surface on which vegetation is being cut. The spool, bumper and the intermediate member, as an assembly, are spring loaded downwardly with respect to the spinning housing. Extending inwardly from the intermediate cylinder are tangs which ride 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 which extend downwardly to the next vertical cam surfaces. The net effect is that the spool, connected to the intermediate members, and the housing, connected to the cam member, rotate relative to each other to allow a predetermined length of flail to feed out as a result of centrifugal force acting on the flail. Since a serpentinous cam is used, a single bump can produce only one segment of flail feedout, and does so without the crunching engagement of the prior art dog clutches. 
     Despite the improvement in the rotary mowing and trimming device of U.S. Pat. No. 4,259,782, the specific construction of the tangs and the serpentinous cam slot in that device is designed to result in stress concentrations in the engaging members and, as a result, an abrupt and discontinuous operation of the feedout assembly which results in potential wear of the assembly parts, as well as non-smooth operation of the mowing device. 
     Accordingly, it is an object of the subject invention to provide an improved automatic flail feedout device which is reliable, easy and economical to manufacture, and which operates smoothly so that its performance does not degrade with use. 
     It is a further object of the subject invention to provide a mower which feeds out a predetermined amount of flail when desired in a smooth and consistent manner, without resulting in stress concentrations on the individual parts forming the feedout assembly. 
     SUMMARY OF THE INVENTION 
     The cutting head for a rotary trimmer of the subject invention is an improvement of the feedout mechansim of U.S. Pat. No. 4,259,782 and employs the same basic structural architecture. Briefly, the subject trimmer includes a hollow handle with an attached drive means that is connected to a spinning 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. 
     The feedout assembly includes 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 thereof. The follower member is coupled to a cam having offset tangs for controlling the amount of filament fed out of the cutting head to a predetermined length. The offset prongs are also configured to have a base that is wider than the rounded tip thereof to form a taper from the base to the tip. Furthermore, the taper of each offset prong is complimentary to the taper of each tang. The configuration of the subject invention results in better force distribution and the reduction of stress concentrations when the tangs and prongs engage each other, thereby resulting in a smoother feedout of the filament and a structurally enhanced feedout assembly. A biasing spring maintains the follower member and the cam properly positioned within the feedout assembly so that the filaments are fed out upon tapping of the subject cutting head against the ground. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a mower cutting head constructed according to the prior art and, more particularly, as disclosed in U.S. Pat. No. 4,259,782; 
     FIG. 2 is an enlarged partial cross-sectional view of the flail feedout of the prior art mower cutting head of FIG. 1; 
     FIG. 3 is an exploded view of the flail feedout of the prior art mower cutting head of FIG. 1; 
     FIG. 4 is an exploded perspective view of the flail feedout assembly of the subject invention; 
     FIG. 5A is a top plan view of the cam member of the flail feedout assembly of the subject invention; 
     FIG. 5B is a side elevational view of the cam member of the flail feedout assembly of the subject invention; 
     FIG. 5C is a bottom plan view of the cam member of the flail feedout assembly of the subject invention; 
     FIG. 5D is an exploded plan view of a tang of the cam member; 
     FIG. 6A is a top plan view of the follower member of the flail feedout assembly of the subject invention; 
     FIG. 6B is a side elevational view of the follower member of the flail feedout assembly of the subject invention; 
     FIG. 6C is a cross-sectional view of the follower member taken along lines  6   c — 6   c  of FIG. 6A; 
     FIG. 7A is a side elevational view of the spool member of the flail feedout assembly of the subject invention; 
     FIG. 7B is a top plan view of the spool member of the flail feedout assembly of the subject invention; and 
     FIG. 7C is a cross-sectional view of the spool member taken along lines  7   c — 7   c  in FIG.  7 B. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-3 illustrate the prior art cutting head  10 ′ as disclosed in U.S. Pat. No. 4,259,782. In the operation of the prior art cutting head  10 ′, when the bumper  44 ′ is bounced or momentarily pressed on the ground, knobs  214  and  216  are forced out of the cutouts  210  or  212 , wherein they are retained against the force of spring  82 ′ to hold the spool in the assembly, and knobs  214  and  216  ride upwardly in the grooves  200  and  202  against the force of the biasing spring  82 ′. The latter presses downwardly on the upper surface  220  of a follower member  218 . Rotation of the spool assembly  42 ′ is slowed or stopped during the bounce or pressing of the bumper  44 ′ against the ground to allow line to feed out. When the bumper  44 ′ is no longer pressed against the ground, the knobs  214 ,  216  are spring-urged back into cutouts  210 ,  212  to again retain the spool. As shown in FIG. 1, the knobs  214  and  216  are generally of cylindrical shape and are oriented to extend radially outwardly with respect to the axis  221  of the follower member  218 . 
     Follower member  218  also includes four uniformly spaced upwardly facing tangs  222  adjacent the upper surface  220  of the follower member  218 . The position and spacing of the tangs  222  determine, in part, the amount of filament segment  20 ′ released per filament release cycle when the bumper  44 ′ is bounced or momentarily pressed on the ground. The tangs  222  ride in a serpentinous cam groove  224  formed adjacent the upper surface  226  of a cam member  228 . The groove  224  has radially oriented lower surfaces  230 ,  231  and vertical abutment portions  232  at 90° to the bottom surfaces  231 . As illustrated in FIGS. 1-3, the vertical abutment portions  232  form a sharp right angle connection with both the bottom surfaces  231  and the upper surfaces of the tangs  236 . The upper surface  234  of the cam groove  224  is formed by a plurality of radially outwardly oriented generally rectangular tangs  236  so that the serpentinous path of the cam groove  224  jogs at right angles. As shown in FIGS. 2 and 3, the tangs  222  are restricted to motion within the cam groove  234  and, depending upon the rotational direction of the spool  24 ′, the tangs  222  move from one adjacent vertical surface  232  to the next facing vertical surface in the same direction. The tangs  222  include sidewardly facing planar abutment surfaces which assist in reducing the hammering pressures when the tangs  222  move from abutment with one surface  232  to the next surface. 
     The cam member  228  is rotated by threaded attachment by way of an insert  62 ′ molded into the member  228 . The latter can be removed from the screw  60 ′ by application of torque to a nut shaped portion  244  molded in the bottom surface  246  of the member  218 . 
     FIGS. 4-7 illustrate the flail feedout mechanism or assembly according to the subject invention. As indicated above, the flail feedout mechanism assembly of the subject invention is employed in a cutting head for a rotary trimmer and employs the same basic structural architecture as described in U.S. Pat. No. 4,259,728, except for the structural improvements embodied in the flail feedout mechanism assembly  300 , as illustrated in FIG.  4 . The flail feedout assembly  300  of the subject invention basically comprises a follower member  302 , a cam member  304 , and a spool member  306 . As illustrated in FIG. 4 as well as FIGS. 6A,  6 B and  6 C, the follower member  302  is of generally cylindrical configuration having four uniformly spaced, upwardly facing tangs  308  adjacent 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 . As shown in FIG.  4  and FIGS. 6B and 6C, the knobs  312  are disposed intermediate the sidewall of the follower member  302 , with each knob  312  being of cylindrical configuration. As shown in FIG. 6A, the knobs  312  are uniformly spaced in a radial direction at an angle of 60° relative to each other. As also shown in FIG. 6A, two diametrically opposed knobs  312  are disposed in the same plane as two diametrically opposed tangs  308 . 
     Referring to FIGS. 5A-5D, the cam member  304  has a lower, annular plate  320  of a diameter slightly less than the inner diameter of the cylindrical follower member  302 . Angular plate  320  includes a central hole  322 . Formed integral with the plate  320 , and formed adjacent the upper surface of the cam member  304 , is a serpentinous cam groove  324  whose function is similar to that of the cam member  224  described above. The groove  324  has radially oriented lower surfaces  326 ,  328  and vertical abutment portions  330  disposed at about 900 to the bottom surfaces  328 . The upper surface  332  of the cam groove  324  is formed by a plurality of radially outwardly oriented tangs  334  so that the serpentinous path of the cam groove  324  jogs at right angles. 
     As shown in FIGS.  4  and  5 A- 5 D, the tangs  334  are restricted to motion within the cam groove  324 . The tangs  334  move from one adjacent vertical surface  330  to the next facing in the same direction. The tangs  334  include sidewardly facing planar abutment surfaces which assist in reducing the hammering pressures when the tangs  334  move from an abutment with one vertical surface  330  to the next. 
     The tangs  308  of the follower member  302  and the tangs  334  of the cam member are different in configuration from the tangs  222  and  236  of the prior art device. More specifically, instead of being generally rectangular in plan form, as illustrated in FIG. 5D, each tang is of a truncated, bell-shaped configuration and thus is defined by multiple different radiuses. As a result, each tang  308 ,  334  is configured to avoid stress concentrations upon impact of the cam member and the follower member during a flail feedout operation. As particularly shown in FIG. 5D, the radius of each tang at its base is 0.060 inches whereas, at its radially outward position, the radius is 0.125 inches. This relationship of approximately 2:1 affords additional structural strength to the tangs, as well as avoiding stress concentrations, and results in a smoother, more efficient flail feedout mechanism. 
     Referring to FIGS.  4  and  7 A- 7 C, 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 . 
     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 specifications together with the accompanying drawings and claims. 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 which is limited only by the claims which follow.