Abstract:
A trimmer head having pivoting line holders comprises a single unitary molded housing having at least one recessed cavity located on the upper surface which is shaped and sized to receive a pivoting line holder, the recessed cavity includes reinforcement members for securely retaining pivoting line holder therein via insertion of a metal bearing ring which allows for free rotation of pivoting line holder about its central axis within recessed cavity; a method for installation of pivoting line holders within a trimmer head is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/955,949 filed Mar. 20, 2014, which is incorporated by reference as if fully rewritten herein. 
     
    
     FIELD OF INVENTION 
       [0002]    The subject of this invention relates to trimmer heads for rotary trimmers using monofilament as a means for cutting vegetation; and, more specifically it relates to an improved method of assembling trimming heads where the trimmer heads include a means to hold folded strips of trimmer line. These means are capable of pivoting to minimize line breakage upon impact of the line with solid objects and dense vegetation. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are many names commonly used interchangeably for the monofilament line used for cutting vegetation, not limited to the following: trimmer line, weed trimmer line, grass trimmer line, monofilament line, string trimmer line, strimmer line, cutting line, line, line strips, strips, flails, and weed whacker line. Monofilament line is sold in many different cross-sectional shapes and is made from many different types of nylon plastic. 
         [0004]    The prior art, including U.S. Pat. Nos. 7,603,782 and 7,743,511 (hereby included by reference for their teachings), discloses trimmer heads with line holding mechanisms (line holders) capable of pivoting on a vertical axis. There are many names commonly used for these line holders including, but not limited to posts, pivoting line holders, pivoting posts, pivot posts, line holding mechanisms and pivoting line holding mechanisms. All of these terms may be used interchangeably. These terms are used with line holders that are all designed to pivot about a vertical axis. However, some of these terms are also used with line holders that are not designed to pivot. 
         [0005]    The prior art discloses a pivot post having a flange at the bottom of the post. This post is operatively connected to the trimmer head housing by loosely sandwiching the post&#39;s flange between a lower head portion (cover) and an upper housing portion of the trimmer head. The post is held such that its relative position on the head is fixed, the pivot post can rotate 360 degrees about a central vertical axis, but it cannot move vertically. 
         [0006]    Certain commercialized products incorporating pivoting posts include line-holding mechanisms having the basic shape of a round post with a circular flange at the lower end. The top end of the post is beveled (slanted) on two opposite sides with two straight-through passageways for insertion of the trimmer line, where the passageways connect the two beveled portions. A representation of these prior art commercially available posts can be found as reference numeral 50 of the &#39;511 patent. 
         [0007]    Some of the commercially available trimmer heads utilizing the construction method of sandwiching the pivot post flange between lower and upper head portions include the PivoTrim™ X2, PivoTrim™ Ugly™ Head, and the PivoTrim™ Classic, PivoTrim™ Pro, and the PivoTrim™ Hybrid. These products are sold by Shakespeare Company, LLC. 
         [0008]    The prior art also discloses pivoting line holders which mount to the top surface of the trimmer head and are assembled to the trimmer head housing using threaded fasteners such as bolts. These line holders pivot about the axis of the fastener. The trimmer line is completely held at the periphery of the holder and the center of gravity of the holder is not aligned with the axis of rotation. 
         [0009]    The prior art further discloses a trimmer head which builds upon this latter type of pivot post design and is disclosed in U.S. Publication 2014/0202009, hereby disclosed by reference. This trimmer head requires custom manufactured fasteners which are intended to be periodically removed and reinstalled by the consumer to allow the use of blades instead of line holders. 
       SUMMARY OF THE INVENTION 
       [0010]    The current proposed invention is a trimmer head and method of assembly utilizing pivoting line holders of the type where the center of gravity (CG) of the post is vertically aligned with its vertical axis of rotation. The trimmer heads in this specification require fewer steps for assembly than prior art trimmer heads. These simplified head designs are of value because fewer components need to be manufactured per head, fewer steps are required for assembly of the head, and large custom machined fasteners are not required. Therefore, the invention is also of value because it is inexpensive to produce. 
         [0011]    One objective of this invention is to provide a trimmer head that is inexpensive to manufacture that utilizes pivoting line holders, where the center of gravity of the line holders is aligned with the posts vertical axis of rotation. 
         [0012]    Another objective is to provide a simple method for assembling a trimmer head designed to utilize pivoting line holders which hold folded strips of line. 
         [0013]    Another objective is to provide a trimmer head which is light weight and suitable for use with lighter duty trimmers. 
         [0014]    Another objective is to provide a trimmer head design where a bearing ring, sized to hold a pivoting post in operative position, can be precisely positioned and tightly held, and yet allow unobstructed rotation of the line holder. 
         [0015]    Another objective is to provide a trimmer head that holds a folded strip of trimmer line using a line holder that can freely pivot. 
         [0016]    Another objective is to provide designs for trimmer heads mounted with pivoting line holders based upon a housing that can be molded as one piece. 
         [0017]    Another objective is to provide a simplified method of assembly for the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0018]      FIG. 1  shows perspective view of a trimmer head assembled pursuant to the method of the present invention. 
           [0019]      FIG. 2  shows an upper perspective view of the main housing of the trimmer head shown in  FIG. 1 . 
           [0020]      FIG. 3  shows a lower perspective view of the main housing of the trimmer head shown in  FIG. 1   
           [0021]      FIG. 4  shows a cutaway of a side view of the main housing of the trimmer head shown in  FIG. 1 , taken through the pivot post. 
           [0022]      FIG. 5  shows a cutaway perspective view of a portion of the trimmer head shown in  FIG. 1 . 
           [0023]      FIG. 6  shows an upper perspective view of a second embodiment, assembled pursuant to the method of the present invention. 
           [0024]      FIG. 7  shows a bottom view of the trimmer head shown in  FIG. 6 . 
           [0025]      FIG. 8  shows an upper perspective view of the main housing of the trimmer head shown in  FIG. 6 . 
           [0026]      FIG. 9  shows a side perspective view of a pivot post assembly for use with the trimmer heads shown in  FIG. 1  and  FIG. 6 . 
           [0027]      FIG. 10  shows a lower perspective view of the pivot post shown in  FIG. 9 . 
           [0028]      FIG. 11  shows an upper perspective view of a portion of the main housing and demonstrates a first step of the assembly process of the present invention. 
           [0029]      FIG. 12  shows the main housing of  FIG. 11  and demonstrates the successive step of installing the pivot post. 
           [0030]      FIG. 13  shows the main housing of  FIG. 12  and demonstrates the final step of installing the metal ring. 
           [0031]      FIG. 14  shows the metal ring of  FIG. 13  (also known as the bearing sleeve), 
           [0032]      FIG. 15  shows a cutaway of the receptacle for receiving a pivot post and bearing sleeve, with the bearing sleeve fully inserted. 
           [0033]      FIG. 16  shows a folded strip of trimmer line. 
           [0034]      FIG. 17  shows a third embodiment of a trimmer head assembled pursuant to the method of the present invention. 
           [0035]      FIG. 18  is a cross-sectional view of the trimmer head shown in  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]      FIGS. 1 ,  6  and  17  show three embodiments of trimmer heads assembled pursuant to the method of the present invention. The trimmer head in  FIG. 1  is a perspective view of the first embodiment of assembled trimmer head  10 , shown with a single pivot post  116 .  FIG. 6  is a perspective view of the second embodiment of the assembled trimmer head  110 , shown with two pivot posts  116 . The pivot posts  116  in both embodiments are of the same design. Variations of the trimmer head which have three or more equally spaced pivot posts are also within the scope of this invention.  FIG. 17  shows a trimmer head assembled with three pivot posts using the assembly method of this invention. 
         [0037]    A unique feature of the two trimmer heads  10  and  110  is that the housing  12  can be molded as a single piece. Compared to prior art trimmer head housings constructed of two pieces—having both upper and lower head portions—the design of trimmer heads  10  and  110  eliminates one of the molded pieces, eliminates the need for screws to join the two head portions, eliminates some of the assembly costs associated with two-piece housing constructions, and minimizes the trimmer head weight. All of these refinements reduce the cost of a trimmer head manufactured with pivoting line holders pursuant to the presently disclosed assembly method. 
         [0038]      FIGS. 2 and 3  show two alternative views of housing  12  which may be used by trimmer head  10 . The housing as shown in  FIG. 2  has a central opening  134  for receiving a threaded stem (not shown) from a string trimmer machine. A fastener (not shown) with a hexagon head is inserted into the hexagonal-shaped cavity  136  (see  FIG. 3 ). The housing  12  is rotated until the fastener fully tightens onto the threads of the trimmer stem and against the inside of the housing. The first embodiment is designed to hold one pivot post  116  in the recessed opening  160 . The housing is designed so that extra mass is molded into the housing opposite the recessed opening  160 . This extra mass is added to balance the head so that it can be spun at high speeds (typically 8,000 to 10,000 rpms) without vibration. 
         [0039]    The housing  12  has a series of ribs  138  which strengthen and stabilize the vertical and horizontal portions of the housing. These ribs are shown positioned on the upper side of the housing. However, the housing could also be designed to be smooth on the upper side with the strengthening ribs positioned on the underside of the housing. 
         [0040]    The line holding mechanisms  116  (also called pivot posts) are held in recessed cavities  160  by a metal ring  20 . The metal ring is press-fit into the cavity  160 . This metal ring  20  functions as a bearing sleeve and provides a wear resistant surface. The pivot post design  116  is merely representative of one of many types of pivot posts that could be used with the invention. There are numerous pivot post designs that could be installed into the housing of the first embodiment  10  and the second embodiment  110  including those pivot post designs commercially available so long as the bottom portion of the post was modified to allow installation into the recessed cavity of the present invention. 
         [0041]    The pivot posts  116  are designed to hold a folded strip of trimmer line  132  as shown in  FIGS. 1 and 6 . A representation of the trimmer line  132  is shown in  FIG. 16 . The strip of trimmer line has two distal ends ( 154  and  156 ) and is folded at a point between the two distal ends. In  FIGS. 1 and 16 , one end  156  of the trimmer line is allowed to extend further than the second end  154 . In  FIG. 6 , both legs of the folded strip of trimmer line are the same length and the pair of distal ends are positioned adjacent to each other. 
         [0042]    When installing the strip of trimmer line  132  into the pivot post  116 , the two distal ends are threaded through the two openings  122   a  and  122   b  (see  FIG. 9 ), and then the ends are pulled until the inside radius  158  of the folded line  132  is pulled tight against the metal insert  115 . The line is shown installed in the head in  FIGS. 1 ,  4 ,  5 ,  6  and  7 . 
         [0043]    The housing  112  for the head shown in  FIG. 6  does not require any extra mass for counterbalance. The housing  112  for this second embodiment has two recessed cavities  160   a  and  160   b  (see  FIG. 8 ), each for receiving a pivot post  116 . Ignoring the orientation of the pivot posts, the head  110  is symmetrical about a vertical plane passing through the vertical central axis of rotation of the two pivot posts, and symmetrical about a vertical plane perpendicular to the first plane which also passing through the midpoint between the two posts. 
         [0044]      FIG. 7  shows a bottom perspective for the second embodiment trimmer head  110 . The hexagon cavity  136  is the same for both trimmer heads  10  and  110 ; however, they could be designed differently. For example, they could be designed to work with a larger nut or bolt size. There are also other methods for attaching a trimmer head to a string trimmer machine which are commercially practiced. These alternative methods could likewise be used. Additionally, the housing could also have a perimeter shape other than round. The perimeter could be oval, square or rectangular with rounded corners, three-legged like the Ugly™ Head, or any of a variety of head shapes. It is also possible to have two or more pivot posts that are not equally spaced so long as mass is added to balance the head to prevent vibration during rotation. 
         [0045]    The next discussion will reference  FIGS. 5 ,  9 ,  10 ,  11 ,  12 ,  13 ,  14  and  15 . The cavity  160  is designed with a series of radial ribs  150 . At the base of these ribs is a ridge molded into the lower portion of the cavity  160 . This ring shaped ridge has an upper edge  140 . The metal bearing ring  20  has an outer edge  152 . The opening between the ribs  150  is sized such that the metal ring  20  is held firmly between the ribs  150 . Additionally, the lower edge  152  of the metal bearing ring  20  will come to rest against the upper edge  140  of the molded ridge, which allows for precisely positioning the bearing ring  20  in the cavity  160 . The outer diameter of the flange on the pivot post is smaller than the inside diameter of the recessed cavity  160 , but larger than the inside diameter of the metal bearing ring  20 . Additionally, the height of the flange on the pivot post is less than the height of the ring molded into the bottom of the recessed cavity  160 . This allows the pivot post to freely spin inside of the metal bearing ring, and yet it cannot come out of the recessed cavity  160 . 
         [0046]    Prior to inserting the bearing ring  20  into cavity  160 , the pivot post (or pivot post assembly) must first be placed in the cavity  160 . The cavity can optionally contain a post  144  (see  FIG. 5 ) upon which the line holder  116  can spin. In this case, the pivot post  116  must have a recessed opening  146  (see  FIG. 10 ) to allow for the free spinning of the pivot post  116  on the post  144 . The pivot post  116  has a flange  126  such that part of the upper edge  142  of the flange is below part of the lower edge  152  of the bearing ring  20  when installed. Additionally, the combination of the cavity  160  with the ring  20  installed allows sufficient space so that the flange  126  of the pivot post  116  is loosely held such that the pivot post is allowed to spin freely about its central vertical axis. 
         [0047]    The embodiments presented are also unique in that the assembly of the head is simplified. For the commercial trimmer heads currently offered by Shakespeare Company, LLC, the following six steps are required to assemble the trimmer heads: (1) position the upper portion of the head in an upside down orientation; (2) press a metal ring into each of the openings of the upper portion of the head; (3) place the molded pivot posts in the metal rings; (4) place the lower cover over the upper housing portion and align the passageways for the screws; (5) while holding the lower cover to the upper housing, re-position the entire unit by flipping these over; (6) install screws to connect the cover to the upper housing. The improved method of assembly and improved trimmer head requires only the following three steps for assembly: (1) position the head housing right side up (see  FIG. 11 ); (2) place the pivot posts  116  into the cavities  160  (see  FIG. 12 ), and (3) press the rings  20  into the cavities  160  (see  FIG. 13 ). 
         [0048]    The improved method disclosed above applies for a pivot post molded as a solid piece of plastic. In the above improved method as well as the currently available method of assembly, a press is typically used to install the bearing rings. 
         [0049]    The novel and improved three-step assembly method allows for the following alternate method to assemble the head without the use of a press to push the bearing rings into position. The housings of trimmer heads are typically molded of nylon plastic. The nylons must be heated &amp; melted prior to the molding step. The nylon will shrink slightly after molding and upon cooling. It is possible to place the pivot post into the recessed cavities  160  immediately after molding and then manually set the bearing rings  20  into position in the cavities  160 . No mechanical press is required. As the nylon cools, the inside diameter of the recessed cavity  160  would become smaller, allowing the cavity to tighten around the bearing ring. This approach to setting the bearing rings combined with the above three step assembly method would eliminate the need for a secondary assembly operation and thus further reduce the cost of the trimmer head. The head could easily be assembled at the molding machine. This assembly process could be done using robotics at the molding machine. 
         [0050]    A variation of the above concepts would include using recessed cavities  160  with smooth walls (no ribs  150 ), and placing ribs on the outer wall of the bearing ring. Additionally, it may be possible to eliminate the ribs  150  entirely if utilizing the shrinkage of the housing after molded to fix the bearing ring in the housing. However, the ribs facilitate installation of the bearing ring into the housing when a mechanical press is utilized, which would be required if the housing is already cooled and thus no shrinkage of the housing is expected after installing the bearing rings. 
         [0051]      FIG. 17  shows an alternate trimmer head embodiment  210  assembled using the same novel methods discussed above. The pivot posts  216  are of a different design than the pivot posts  116 . The common features are the flange and the round shape of the lower portion of the posts. Many different pivot post designs can be assembled using the novel method discussed above. 
         [0052]      FIG. 18  shows a cross-sectional view of the pivot post  216  assembled in housing  212 . The only additional component is a screw  215  mounted adjacent to the pivot post. The screws  215  are not used as part of the assembly method. Rather, these screws are provided as a safety device to ensure that the bearing ring does not pull out of the cavity in which it is mounted. The screw has a flange that overlaps the bearing ring. 
         [0053]    Other variations are within the spirit of the present invention. Thus, while the invention is susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined by the appended claims. 
         [0054]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e. meaning “including, but not limited to”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to or joined together, even if there is something intervening. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
         [0055]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 
         [0056]    All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.