Abstract:
The present invention relates to a three dimensionally fiber-reinforced riser and to the unitary or single-step methods of making the same. In one embodiment (a cross bow riser for example), the riser has an interior support with opposed side members and a front brace. The front brace has a depression centrally located therein. Two side ribs are also provided for structural support. Two pockets each optionally having a divider wall defining a top and bottom section are provided for receiving respective top and bottom pieces of a split limb, when a split limb is used. The riser can be made of a composite material having fibers aligned there within in the directions of the highest stresses for enhancing the structural strength of the riser. Other bow parts or components can likewise be made via composite material as well.

Description:
This application is a divisional application of United States Patent application filed on Jan. 19, 2011 and having Ser. No. 13/008,902, which itself claims priority on and the benefit of provisional application 61/389,968 filed Oct. 5, 2010, the entire contents of each are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an object such as a riser and in particular to a three dimensionally fiber-reinforced riser and to the methods of making the same. 
     2. Description of the Related Art 
     It is a common product design goal to improve or replace conventional items with items having improved characteristics, such as improvements in strength, rigidity and durability, material qualities and economic concerns. 
     One industry where such enhancements are being made is in the archery industry. Archery risers, or simply risers, in the most basic form provide support for archery limbs. The risers can also support accessories such as but not limited to arrow rests, sight components, quivers, wrist straps, cable sliding bars, string stops and other accessories. The limbs bend symmetrically about opposite ends of the riser during the first of two stages of use, namely the draw stage, to store energy which, in turn, can be released during the second stage of use, namely the power stroke, to cause an arrow to be shot or projected from the bow. Stresses of varying magnitudes and orientations develop within the riser during use. Stresses can also develop within the riser during the manufacturing process. 
     One examples of a background patent is United States Patent Number (hereafter “USPN”) U.S. Pat. No. 7,258,113 to Pilpel et al. and titled Thermoplastic Composite Bow Riser, Limb and Cam illustrates a riser for an archery bow that is formed from a fibrous composite material, the matrix of which may be a high heat distortion thermoplastic polymer, a very high heat distortion thermoplastic polymer, or a combination thereof. The riser may incorporate a spine formed from a different polymer or composite than the rest of the riser, or from metal. A method for producing a riser for an archery bow includes the steps of introducing a polymeric composite into a mold from a first end of the mold to facilitate a particular orientation of components of the polymeric composite, molding the polymeric composite to produce a billet that approximates a net shape of the riser, and then machining the billet to the final shape of the riser. While the subject of this invention may work well for its intended purposes, its design and methods of manufacture can be improved upon. 
     Nothing is taught, shown or suggested in this patent as to how parts may be consolidated via a unitary molded composite component. 
     This patent requires the use of a spine made of a different material to achieve a desired structural integrity. The use of a spine can lead to delamination of the thermoplastic, as there exists mismatched physical and thermal properties between the spine and the remainder of the riser. The potential for delamination is enhanced due to the high stress conditions present during operation of the bow. 
     This patent also teaches the manufacture of a two dimensional product or laminate. One disadvantage of having a laminate flat part structure is that the fibers are only positioned in the two dimensions within the plane of the material, and ignores placement and orientation of fibers in the third geometrical dimension (i.e. in the direction of the thickness of the two dimensional laminate structure). In this regard, a two dimensional product of this type may only be useful in plane-stress state conditions. 
     This patent further teaches that the riser is machined to achieve the riser final shape and form. This requirement leads potentially to a host of deficiencies. 
     For example, the machined product may be subject to exposed fiber ends. Any fibers having exposed ends are subject to increased risks of pullout. The pullouts create voids in the product, and also can result in areas of decreased localized material strength. Crack propagation can also be a problem in areas of fiber pullout. 
     Still further, exposed fibers that remain intact can be subject to rapid oxidation and degradation, and there exists a possibility of separation between the fibers and resin. 
     It is particularly problematic that the locations which are most susceptible to these fiber problems are the areas where the material requirements are most demanding, namely, in the regions of the riser having three dimensional structures and where fine details or rapid changes in dimension are present. Examples of these regions include corners, generally curved surfaces and areas of radius. 
     Still further yet, the machined product can form relatively high friction surfaces, or even worse, be subject to varying degrees of friction along the surfaces. This situation is quite problematic for a product such as a bow riser, as arrows typically come into contact with the riser during launch and the changes in friction can alter the trajectory and/or speed of the arrow. 
     Thus, there exists a need for a three dimensionally fiber-reinforced composite riser and methods of making the same that solves these and other problems. 
     SUMMARY OF THE INVENTION 
     The present invention relates to three dimensionally fiber-reinforced riser and to the unitary or single-step methods of making the same. In one embodiment (a cross bow riser for example), the riser has an interior support with opposed side members and a front brace. The front brace has a depression centrally located therein. Two side ribs are also provided for structural support. Two pockets each optionally having a divider wall defining a top and bottom section are provided for receiving respective top and bottom pieces of a split limb, when a split limb is used. The riser can be made of a composite material having fibers aligned there within in the directions of the highest stresses for enhancing the structural strength of the riser. Other bow parts or components can likewise be made via composite material as well. 
     According to one advantage of the present invention, the riser can be formed from a single unitary piece of composite material thereby reducing the number of manufacturing steps and the numbers of parts produced. For example, mounting features for sights, quivers, specialized grips, limb attachments, spring brakes and the like can be incorporated into the present invention without the need for secondary manufacturing operations. Several components can be consolidated via the present invention leading to structural and economic advantages. Accordingly, the economic considerations of manufacture are enhanced by the method of the present invention. 
     According to another advantage of the present invention, the riser is made of a composite material without the need for a spine or other structural enhancing component. To the contrary, the required material properties are provided as a result of the design and manufacturing of the riser of the present invention. 
     Related, given that the riser is formed as a unitary piece, the risks of delamination are eliminated. 
     According to another advantage of the present invention, the fibers are advantageously positioned and oriented in all three dimensions and the respective surfaces. The riser is designed to absorb the stresses applied to it, both during use and manufacturing. In this regard, fibers can wrap into the intricate and/or curvaceous portions of the riser, where structural demands may be the greatest. 
     According to a further advantage of the present invention, the riser is formed in a single molding process instead of being machined. This advantageously provides many advantages including the elimination of fiber pullouts and exposed fibers, both of which can lead to premature failure. To the contrary, the structural integrity of the present invention is enhanced during the manufacturing process as the fibers remains intact. Preselected orientation and quantity of fibers that remain intact advantageously lead to products meeting desired structural goals. 
     Related, residual stresses caused during a traditional machining process are eliminated in the present invention, as the machining process itself is eliminated in the preferred method of making the present invention. 
     According to a further advantage of the present invention, the surfaces of the riser may be uniform and smooth (or have any desired surface characteristics), and may be a relatively low friction surface. This allows an arrow to behave in a predictable and favorable manner at launch. 
     Other advantages, benefits, and features of the present invention will become apparent to those skilled in the art upon reading the detailed description of the invention and studying the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one preferred embodiment of a limb and riser assembly of the present invention. 
         FIG. 2  is a front view of the limb and riser assembly illustrated in  FIG. 1 . 
         FIG. 3  is a top view of the limb and riser assembly illustrated in  FIG. 1 . 
         FIG. 4  is an isolation perspective view of a preferred embodiment of the riser of the present invention. 
         FIG. 5  is a front view of the riser illustrated in  FIG. 4   
         FIG. 6  is a side view of the riser illustrated in  FIG. 4 . 
         FIG. 7  is a schematic view showing the fiber orientation within the riser illustrated in  FIG. 4 . 
         FIG. 8  is a perspective view of an alternative riser embodiment of the present invention. 
         FIG. 9  is a front view of the alternative riser shown in  FIG. 8 . 
         FIG. 10  is a side view of the alternative riser shown in  FIG. 8 . 
         FIG. 11  is a perspective view of the alternative embodiment shown in  FIG. 8  showing a preferred gate location and fiber orientation. 
         FIG. 12  is a reverse perspective view of the alternative embodiment shown in  FIG. 8  showing a preferred gate location and fiber orientation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the invention will be described in connection with several preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     Turning now to  FIGS. 1-6 , it is seen that an embodiment of a riser and limb assembly is illustrated. 
     The riser  10  has opposed ends  11  and  12 , a front  13  and a back  14 , a top  15  and a bottom  16 . It is preferred that the riser  10  is formed as a single integral component in a molding process. The riser  10  is preferably symmetric about a central axis  17 . 
     The riser  10  is made of a unitary piece forming the body  18 . Body  18  has an exterior surface  19  having predetermined surface characteristics. In the preferred embodiment, the surface  19  is relatively smooth. It is understood that different portions of the surface  19  can have different surface characteristics without departing from the broad aspects of the present invention. The surface  19  is unconstrained or independent of the quantity and distribution of the embedded fibers. The body has several intricate portions, and the surfaces and interior volumes of each of the intricate portions are wrapped and/or filled with fibers in a preselected orientation and quantity. Also, it is understood that under molding pressures, it is possible that a thin layer of resin can be passed to the surface to further reduce or eliminate the effect of embedded fibers on the surface ornamentation or characteristics. 
     Turning now to specific geometries of a first preferred embodiment, there is an interior support  20  having side members  21  and  22 , and a front brace  23  is shown. The front brace  23  has a centrally aligned depression  24  therein. Front brace  23  provides a place for a user&#39;s foot to brace the bow during the cocking of the bow. The depression  24  provides clearance for the shot arrow, or bolt, to pass after the shot. 
     A first side rib  30  is provided outside of side member  21 . A second side rib  35  is provided outside of side member  22 . The side ribs  30  and  35  and the interior support  20  combine to form a robust structure. It is appreciated that relatively small ribs having minimized cross-sectional areas are provided herein so as to minimize thermal gradients with resulting subsequent shrinkage and induced internal stresses from the manufacturing process. Also, it is noteworthy that ribs are designed so that the flow of fibers and resin achieve the desired resulting orientations and quantity to provide the designed structural strength. 
     A pocket  40  is provided, and has a divider wall  41  defining a top section  42  and a bottom section  43 . An ear  44  is on the top of the top section  42 , and an ear  45  is on the bottom of the bottom section  43 . A bolt hole  46  is formed through the divider wall  41 . 
     A second pocket  50  is provided, and has a divider wall  51  defining a top section  52  and a bottom section  53 . An ear  54  is on the top of the top section  52 , and an ear  55  is on the bottom of the bottom section  53 . A bolt hole  56  is formed through the divider wall  51 . 
     It is appreciated that the pockets provide full control of the limbs, and also provide for proper limb spacing when split limbs are used. It is further understood however, that singularly recessed pockets can alternatively be used when regular (or non-split limbs) are used without departing from the broad aspects of the present invention. 
     A connector  60  is at the back  14  of the riser for connecting to a stock of the crossbow. 
     A limb  80  can be connected to the riser  10  at pocket  40 . The limb has a top piece  81  and a bottom piece  82  that nest in the top section  42  and bottom section  43 , respectively, of pocket  40 . A hub  83  is provided having a hole  84  there through to allow the limb  80  to be fastened to the riser  10 . 
     A second limb  90  can be connected to the riser  10  at pocket  50 . The limb has a top piece  91  and a bottom piece  92  that nest in the top section  52  and bottom section  53 , respectively, of pocket  50 . A hub  93  is provided having a hole  94  there through to allow the limb  90  to be fastened to the riser  10 . 
     It is appreciated that while one preferred structure is illustrated, that other structures may be used without departing from the broad aspects of the present invention. It is also appreciated that while other components of a crossbow, such as a stock, cams, triggers, trigger box assemblies and/or stock rails are not specifically illustrated, that they nevertheless may be manufactured during the molding process of the present invention without departing from the broad aspects of the present invention. 
     During the design of the riser  10 , the geometric size of a finished riser is first determined based on structural and manufacturing requirements. Next, stress orientation is determined through an analysis such as finite element method analysis. This analysis determines the maximum stresses and orientation of those stresses and displacement that each portion of the riser will be subject to during an external loading condition. 
     Knowing the maximum stresses that each portion of the riser will endure during a loading condition, the flow of the liquid resin and fiber in the mold are modeled using mold flow analytical techniques to achieve a desired fiber orientation within the molded part.  FIG. 7  is representative of a preferred fiber orientation and density of fiber placement in the riser  10 . Gate size and location, injection pressures and mold temperatures are all chosen as they each have an effect on the fiber orientation. Given that the mold is a three dimensional cavity, the fibers will flow on all surfaces to achieve a desired fiber orientation. 
     It is a goal to maintain relatively small cross-sectional areas within the riser to prevent thermal imbalances and shrinkage, yet maintain sufficient size to allow for proper fiber flow and orientation. 
     Resins suitable for use in the present invention include engineering polymeric resins such as, but not in any way limited to, Nylons (PA) and their many compounds, polyurethanes (PU), PPS, PES, PEI, Epoxy and Polyesters. In this regard, any suitable resin may be used without departing from the broad aspects of the present invention. 
     Fibers for use with the present invention are preferably E-Glass, S-Glass, Aramid or Carbon. It is understood that other fibers may be used without departing from the broad aspects of the present invention. It is preferable that the fibers are long fibers having a length greater than 1 mm. It is even more preferred that the fiber length is greater than or equal to 3 mm. The fibers, as noted above, are distributed within the body in a three dimensional distribution pattern in predetermined orientations and densities. In one production embodiment, the fibers have a starting length of approximately 15 to 25 mm. The lengths are reduced during manufacturing due to attrition in the process and passage through orifices such as gates and runners. 
     It is understood that one preferred process as described herein is injection molding. Yet, other processes, such as compression molding or compression injection molding can be used without departing from the broad aspects of the present invention. 
     It is preferred that injection temperatures are within the range of 280 to 350 degrees Celsius. It is preferred that the mold temperature is within the range of 90 to 180 degrees Celsius. 
     Injection speeds of 50 to 70 mm/sec are preferred, as are injection back pressures of 25 to 50 psi. 
     These manufacturing parameters are preferred because they provide an environment suitable for a high degree of fiber length retention, yet allow for intended fiber distribution and orientation within the body. In this regard, it is readily understood that the fiber distribution and orientation can be variable within the volume of the body. 
     Turning now to  FIGS. 8-12 , it is seen that a preferred embodiment of an alternative riser  110  is provided. The riser  110  has a first end  111 , a second end  112 , a front  113 , a back  114 , a top  115  and a bottom  116 . Riser  110  is a three dimensional unitary structure having a body  118  with an external surface  119 . Riser  110  is illustrative of a typical compound bow riser. It is appreciated that riser  110  can have any desired shape without departing from the broad aspects of the present invention. Surface  119  can have any desired characteristics. 
     The riser  110  has a pocket  120  at the top  115  of the riser  110 . Bolt hole  121  is provided for connecting a limb (not shown) to the riser. 
     The riser  110  also has a pocket  130  at the bottom  116  of the riser  110 . Bolt hole  131  is provided for connecting a limb (not shown) to the riser. 
     The body  118  of the riser  110  defines several riser features, including a grip  140 , sight mounts  150 , cable rod mounts  160  and an arrow shelf  170 . It is appreciated that these and any other desired features can be made in a single three dimensional unitary piece in a molding process similar to the process described above. 
     Looking now specifically at  FIGS. 11 and 12 , it is seen that preferred gate locations  180  and  180 A, respectively, and the resulting fiber orientations are illustrated. Specifically, it is seen that fibers are oriented initially generally perpendicular to the gate locations and spread in line with the flow of the resin and fibers. The fiber orientations then follow the contours of the riser and hence wrap fully about intricate components of the riser as the fibers and resin flow to fill the mold cavity. 
     According to another aspect of the present invention, the risers  10  and  110  can be designed for specific performances such as draw weights and/or arrow speeds. For example, the risers can be designed and rated for specific draw weights including but not limited to 40-70 lbs. for compound bows or 180 to 220 lbs. for cross-bows. Also, target arrow speeds including but not limited to the range of 350-410 feet per second can be designed. It is understood that the stresses from these or other loads can be determined wherein risers with requisite strength (due to dimensions, fiber orientations and quantity) can be produced to effectively withstand the stresses. 
     Thus it is apparent that there has been provided, in accordance with the invention, a three dimensional composite riser and methods of making the same that fully satisfies the objects, aims and advantages as set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.