Abstract:
A striking face for golf clubs, such as a driver, iron or putter comprising a plurality of bars retained in the club head body and forming the striking surface. The bars which comprise the striking face according to the invention may be designed and arranged to provide enhanced performance of a golf club. The bars may also be machined economically before assembly of the golf club head to provide a precision grooved striking face at reduced cost.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation application of application Ser. No. 10/616,984, filed on Jul. 11, 2003, now abandoned the contents of which are hereby incorporated by reference in their entirety for all purposes. 

   FIELD OF THE INVENTION 
   This invention relates to golf club heads for golf clubs such as drivers, irons and putters. 
   BACKGROUND OF THE INVENTION 
   Many proposals have been made to design golf clubs which provide improved control over, and feel for, the golf ball, for example by providing grooves on the impact face of the golf club head. Reference may be made, for example, to U.S. Pat. Nos. 1,383,654, 1,452,695, 1,494,494, 5,176,384, 5,358,249, 5,405,136, 5,542,675, 5,766,093, 5,807,190 and 6,007,435. The disclosure of each of those patents is incorporated herein by reference for all purposes. Not all of the proposals comply with the USGA Rules of Golf, Rule 4 and Appendix II, which require that, for clubs other than putters, “the whole of the impact area” of the club face “must be of the same material” and that impact area markings, such as grooves, should comply with certain requirements. The “impact area” of a club head is referred to herein as the “impact face”. 
   SUMMARY OF THE INVENTION 
   In a first preferred aspect, this invention provides golf club head comprising 
   (1) a club head body, and 
   (2) a faceplate which
         (i) provides an impact face and   (ii) comprises a plurality of bars which can be individually deflected, without permanent damage, in a direction perpendicular to the impact face when the impact face strikes a golf ball.       

   In a second preferred aspect, this invention provides a method of making a golf club head, for example a golf club head according to the first preferred aspect of the invention, the method comprising 
   (A) providing a club head body; and 
   (B) forming an impact face on the club head body, the impact face comprising, after step (B), a plurality of bars which can be individually deflected, without permanent damage, in a direction perpendicular to the impact face when the impact face strikes a golf ball. 
   The composition, dimensions and arrangement of the bars are preferably chosen so that the impact face has a desired response when a golf ball impacts it at different positions across the insert. In some embodiments, the sidewalls of the bars are pre-shaped so that adjacent sidewalls provide grooves of desired dimensions on the impact face. For example, half grooves are machined onto the appropriate sidewalls so that, when the bars are incorporated into the faceplate, the adjacent half grooves form grooves on the impact face. This allows individual bars to be economically mass produced before being incorporated into an inset in the face of a club head. In some embodiments, the bars are retained in the recess by a dovetail geometry on the ends of the bars. In a preferred embodiment, a top and/or bottom retainer element is pressed into place in the dovetail in order to lock the bars into position. 
   Preferred club heads of the invention can provide important advantages by comparison with conventional golf clubs in which the impact face is provided by a single piece of material (and, therefore, has a “trampoline” geometry with a centroidal sweet spot outside of which performance drops off quickly). Such advantages can include:
         a more desirable feel and larger “sweet spot” which results in improved uniformity of response upon impact for off-center hits and a reduction in the effect of off-center hits on the path of the struck ball, and   a desired balance between maximized distance and control.       

   Preferred club heads of the invention, particularly club heads for irons and drivers, conform with the USGA Rules of Golf with respect to grooves on, and uniformity of material of, the impact face. 
   Preferred embodiments of the method of the invention provide an improved method of manufacturing a club head having grooves in its impact face. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows schematically an exploded view of a golf club head incorporating a plurality of bars in accordance with the invention. 
       FIG. 2  shows a detail section view of the edge of the recess of  FIG. 1  at area II including a dovetail mating surface. 
       FIG. 3  shows a detail view of two adjacent bars in cross section. 
       FIG. 4  shows an exemplary embodiment of an assembled “bars” iron. 
       FIG. 5  shows a cross-section through the line V-V of  FIG. 4 . 
       FIG. 6  shows a cross-section through the line VI-VI of  FIG. 4 . 
       FIG. 7  shows an expanded view of two bars in area VII of  FIG. 6 . 
       FIGS. 8-10  show exemplary alternative embodiments according to the invention wherein the bars are “V” shaped and form a chevron pattern. 
       FIGS. 11-12  show two exemplary “V” shaped bars. 
       FIGS. 13-14  show alternative embodiments wherein the bars are inserted by a relieved end slot and retained by a single press-fit bar. 
       FIGS. 15-16  show an example of a multi-layer bar in two views in accordance with the invention. 
       FIG. 17  shows, in detail, a bar end design according to a preferred embodiment of the invention. 
       FIGS. 18-22  show various exemplary bar end sections in perspective wherein the bar thickness is varied across the width of the bar. 
       FIGS. 23-28  show various exemplary bars in accordance with the invention wherein the bar cross section is varied along the long dimension. 
       FIGS. 29-32  show in cross section several exemplary embodiments of iron type clubs according to the invention incorporating stacked bars of varied thickness. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring for example to  FIGS. 1-14 , the club head body  1 , 21 , 31 , 42  may be made of any material suitable for the construction of golf clubs and may include additional features such as a sole-plate on wood type clubs as are known in the art. The club head body  1  has a recess  2  in its front face  3 , 23 , 33 , 45  and optionally a cavity  4 , 24  or through hole within the recess, behind the impact face. A plurality of machined or otherwise formed bars  8 , 28 , 39 , 40 , 48 , 49  are fit contiguously into the recess in the face of the club head to form a faceplate having an impact face. The bars have three primary dimensions, length, width, and depth, with a frontwall  13  bounded by the two largest dimensions, length and width, sidewalls  12  bounded by the length and depth, and endwalls bounded by the width and depth. The depth dimension may be uniform or variable lengthwise as may the thickness of the material. Each endwall  11  may comprise a single surface which is perpendicular or angled with respect to the frontwall, e.g., the endwall can be shaped to form an interlocking surface which can engage a surface  5 , 25  cast or machined into the edge of the recess in the club head body thereby retaining the bars in the recess. The bars can be individually deflected in the direction perpendicular to the impact face when the impact face impacts a golf ball, and are preferably assembled in the recess with the sidewalls  12  in contact with each other. The frontwalls may be polished or treated mechanically or chemically to provide a textured impact face. The bars may fill the recess or be bordered by retainers which can be shaped to match the unfilled portion of the recess. If desired, a closed cavity may be provided beneath the bars, or the backside of the bars may be partially exposed through an opening in the rear surface of the club head. 
   The side edges  6  of the bars&#39; frontwalls  13  may be machined before assembly such that a groove  10 , 26  is formed between adjacent bars and/or between the bars and any retainers  7 , 9 , 27 , 29 , 34 , 35 , 44 , 47 . A bar  37 , 48  side edge may be machined to provide a full length groove between adjacent bars. Alternatively, the bars  38 , 49  may be machined to provide a less than full length groove between adjacent bars. The bars may also be machined to form grooves in the frontwalls between the edges. The groves may be any shape (e.g., V shaped, square, or round); although, the V shaped grooves formed by two adjacent beveled edges are preferred. This allows for the economical production of precision machined grooves on a golf club face. 
   The bars may be retained in position in a club head by an interlocking arrangement, by bonding such as metallurgical or adhesive bonding or a combination thereof. For example, the bars may be retained in the club face by mating edges  5  forming a dovetail or other suitable geometry cast or machined into the recess  2  in the club head, e.g., spaced apart vertically or horizontally extending mating surfaces at opposed edges of the recess. In a preferred embodiment, the assembly of a “bars” iron is as illustrated in  FIGS. 1-3 . A dovetail slot at opposed ends of a recess is machined into the heel  15  and toe  14  of the club head face  3 . A bottom retainer  9 , shaped at the bottom edge  19  to match the geometry of the bottom  17  of the club and having an interlocking surface at each end shaped to engage the dovetail slot, is press fit into the bottom of the dovetail. Typically six to eight bars  8  with the adjacent edges  6  machined at a 45 degree angle to a depth of 0.01 to 0.02 inches are stacked tightly in the dovetail slot. A retainer  7  shaped at the top edge  18  to match the geometry at the top  16  of the club head and having an interlocking surface at each end shaped to engage the dovetail slot is press fit into place above the stack securing the bars in position. 
   As illustrated in  FIG. 4 , a bars iron may present the appearance of a conventional iron with horizontal grooves  26  formed at the contiguous edges of adjacent bars  28 . The club head body  21  is connected to a shaft  22  in the manner well understood in the art. The top and bottom retainers  27 , 29  may be of material similar to the body or may be chosen for aesthetic or mechanical properties. As seen in sectional views ( FIGS. 5-7 ), the bars  28  are backed by a small cavity  24  to permit deflection of the bars upon impact. The mating of the angled bar ends with the dovetail slot  25  at the edges of the recess securely retains the bars in the club head body. 
   A further feature of the “bars” approach to providing an insert for a golf club having an impact face is that the bars can be of any desirable material. For example, in putters it is desirable to achieve a soft feel so a polymeric material with a low modulus of elasticity may be selected for the bars. In an iron type club a highly elastic material with a non-linear modulus like NiTi may be selected for its ability to absorb and recover from high energy impacts. In a wood type club, materials of the highest hardness may be used to maximize flight distance. 
   The mechanical properties of the impact face may be influenced by varying the length, width, and arrangement of the bars. The bars may be rectilinear (i.e. straight) as in FIGS.  1 , 4 , 13 - 14  or shaped with a curve or bend as illustrated in  FIGS. 8-10 . Straight bars may be arranged to extend horizontally as in FIGS.  4 , 13  vertically as in  FIG. 14 , or at an angle relative to the plane of the ground when the club head is properly swung. As seen in  FIGS. 8-10 , “V” shaped bars  37 - 41 , which may be symmetric  39 , 40  ( FIGS. 8-9 ) or asymmetric  41  ( FIG. 10 ), may be assembled in a V-down (FIGS.  8 , 10 ) or V-up ( FIG. 9 ) chevron pattern. As illustrated in  FIG. 10 , retainers  35  may be secured by pins  36 . 
   As illustrated in  FIGS. 13-14 , a retaining dovetail recess need not open to any one side, top, or bottom, of the club head face  45 . Rather, bars  48 , 49  may be inserted via a relieved end slot  43  and retained by a press-fit or pinned final retainer bar  44 ,  47 . Vertical bars, as illustrated in  FIG. 14  may be chosen to be uniform or vary in thickness and/or width towards the toe and heel. Thicker bars at outer ends of the club face may be used to provide hook and slice correction. 
   As illustrated in  FIGS. 15-16 , the bars may be formed of uniform material or of laminated layers  52 , 53 , 54 . Laminated bars  50  may be designed to combine various material properties such as a hard surface with vibration damping, and shape memory. For example a beta titanium front surface layer  52  may be machined with groove forming indentations  55 . This provides the surface with high hardness, abrasion resistance and good strain recovery. This layer  52  may be bonded to a second layer  53  of polyurethane elastomer to provide vibration damping. A third layer  54  of super-elastic NiTi provides the bar  50  with a high degree of strain recovery from deflection and further vibration damping. As another example, thin layers of stainless steel or Beta Titanium may be laminated to provide a bar capable of much higher deflection without permanent damage. Such a bar will maintain contact with the ball longer for energy transfer and enhanced transfer of spin upon impact. Any number of layers may be laminated to form a single bar. The layers may or may not be the same thickness. The front surface layer of all the bars can be of the same material across an impact face to satisfy present USGA rules. 
   As illustrated in  FIG. 17 , in a preferred embodiment of the invention, a bar  61  endwall is angled to form an interlocking surface which can engage the dovetail geometry of the spaced apart edges of the recess. The top may be machined at the side-edge to form a half-groove  62 . Preferably, a small chamfer  168  at the tip of the dove-tail wedge allows the bars to be more easily assembled in the recess and allows greater flexure of the bars at impact. 
   As illustrated in  FIGS. 18-22  the bars  61 , 161  may have a uniform thickness ( FIG. 18 ) or varied thickness across the width of the bars ( FIGS. 19-22 ). The cross section thickness may vary linearly  162  or non-linearly in concave  164 , convex  165 , or stepped  166  shapes. The bar ends  163  are preferably the full uniform thickness in order to engage the club head body at the edges of the recess. Groups of such bars may be chosen for example to vary the thickness profile across the stack as illustrated in  FIGS. 29-32 . 
   As illustrated in  FIGS. 23-28  the bars  61 , 63 , 66 , 67 , 68  may have a uniform ( FIG. 23 ) or varied thickness ( FIGS. 24-28 ) lengthwise linearly or non-linearly. Thinner bars will feel softer and provide a larger zone of uniform response than thicker bars. A bar with a thinner center  67 , 68  will exhibit a larger sweet spot and directional correction for off center impacts. A continuous curve  68  provides a uniform stress distribution across the face while a stepped profile  67  creates discrete zones of response. A bar with a thin profile except a central bump  63  will provide a softened feel with controlled face deflection while retaining a stiff follow-on for distance. A bar with thin outer sections  66  reduces harsh feel of toe and heel impacts. A bar with an asymmetric thickness profile  64  will provide asymmetric response to impact. The thicker end of the bar will be stiffer, thus a golf ball is directed toward the thinner bar end. This design may be used for correction of a chronic hook or slice. Similar considerations apply to the design of stacks of bars such as illustrated in  FIGS. 29-32 . By application of these principles in choosing and stacking bars in a club face, many different golf ball impact responses can be achieved. 
   The invention can be implemented in variations of the foregoing embodiments. For example, the length and direction of the bars could be varied as well within a single club face and/or a configuration of variously treated short bars could be bonded to backing bars and/or provided with mating surfaces in adjacent endwalls. Further, bars of uniform but differently processed (e.g. heat treated) material may used to provide a more even impact response across an impact face and/or smaller bars might be used to heighten this effect, e.g., short bars may be machined to provide mating surfaces at the end walls. Alternatively, short bars may have flat end walls and rely solely on adhesion to a backing bar for retention in the club head. The directions of bars may change one or more times across the impact face. In arrangements of this type, the adjacent endwalls and sidewalls of orthogonal bars may be shaped to provide mating surfaces to retain bars not in contact with the edges of the recess. Bars of mixed shape and orientation may be combined in various arrangements to provide desired properties such as differing groove and surface deflection directions as a function of the impact position on the impact face. Multiple layers of individual bars may be inserted in a club head recess, e.g., an outer layer of bars may be retained in the recess over a backing plate comprising an inner layer of backing bars to provide a fine tuned surface response. The exposed layer may be of a thin, uniform, and elastic material such as NiTi. Backing layers may be of any hardness, cross-section, and arrangement. In a preferred embodiment, the surface bars mate with edges of the recess for purposes of retention. 
   An advantage of preferred embodiments of the invention is the ability to provide a more uniform response to off-center hits. This can be accomplished with the “bars” approach by varying the thickness of the material of the bars over the impact face. Also, the mechanical properties may vary at different points in the impact face while presenting a uniform material surface. For example, bars heat-treated or otherwise processed in different ways either uniformly lengthwise or variably along a bar&#39;s length would allow the impact face to be fine tuned for its response characteristics. Multi-layer bars may incorporate several laminations of different materials specifically chosen for vibration dampening properties or elastic response or both. The various configurations of shape, orientation, and thickness of can be used to offset inherent imbalance and inertia effects in a club when hit off-center or to help compensate an inherently faulty swing. The back-face of the bars may comprise structural features such as a bump or island for the purpose of limiting the travel of a deflected bar upon impact with a ball. 
   Any of the previous examples might be used in conjunction. For example, alternating layers of vertical and horizontal bars might be used to fine tune the response of the impact face. Likewise, any other combination of the exemplary designs might be implemented varying the thickness, width, length, material, properties, and direction. 
   In addition to the forgoing description, the invention and preferred embodiments thereof may be further understood by consideration of the following examples. 
   EXAMPLES 
   Iron with Enhanced Off-Center Impact Response 
   Any of the long (i.e., irons numbered 1 to 5) type clubs may be enhanced for distance with consistency of control by providing an impact face with a larger area of uniform impact response. To this end, a club head body is provided with a recess in the form of a vertical dovetail slot in the face. A polished steel retainer, flat on top with the top front edge machined at a 45 degree angle to a depth of 0.02 inches, contoured on the bottom to match the bottom and sole of the club face, and machined into a dovetail wedge at each end, is press fit into the bottom of the dovetail slot. A series of 10 NiTi bars, about 0.13 inches wide, machined to a 10 degree angle at each end (with a 0.015 inch 45 degree chamfer at the wedge tip) are sized to fit snugly in the dovetail slot. The bars are about 0.1 inches deep at the ends of the frontwall. The side-edges of the front wall are machined at a 45 degree angle to a depth of 0.02 inches. The back side of each bar is machined in a parabolic contour lengthwise with the center of the 6 th  bar machined to approximately half its depth; upper bars are machined more deeply than lower bars in sequence stepwise such that a rear view of the bars stacked in order shows a smooth parabolic contour along the heel to toe direction of the bars and a step-wise linear progression from top to bottom of the stack. The bars are stacked tightly together in the slot forming a precision V shaped groove at each adjacent edge. A top retainer of polished steel, flat on the bottom with the bottom front edge machined at a 45 degree angle to a depth of 0.02 inches, contoured on the top to match the top of the club face, and machined into a wedge at each end to fit tightly in the dovetail slot, is press fit into the top of the dovetail slot. In an on-center impact, the shaped impact deflection focuses energy otherwise dispersed across the face to a center line of thrust. In the case of a slightly off-center impact the shaped deflection of the face re-focuses the flight of ball in the intended direction with minimal loss of distance. The top to bottom thickness progression smooths and expands the sweet spot vertically for high and low impacts. Balls struck at the bottom of the impact face are increasingly directed upward to the desired loft and balls struck near the top of the impact face have a softer feel and longer contact time with the impact face. 
   Irons with Enhanced Spin and Directional Control. 
   An iron type club is provided with an insert of pointing “V” shaped bars as illustrated in  FIGS. 8-10 . The V shape of the bars and grooves control the spin imparted to a golf ball upon impact. Upward pointing V bars ( FIG. 8 ) impart top-spin. Top-spin may be desired to keep a ball&#39;s trajectory low, for example when hitting against the wind, and to increase forward fairway bounce and roll. Downward pointing V bars ( FIG. 9 ) impart backspin. Backspin may be desired to increase aerodynamic lift of a ball in flight or to limit a ball&#39;s forward roll in chip-shots. The V shaped bars are inherently stiffer near the heel and toe, thus directing a ball hit on the heel or toe of the club toward center. An asymmetric chevron can be arranged to stiffen the toe or heel thus selectively shifting the sweet-spot. 
   The various illustrations demonstrate the potential to change properties across the club face while still conforming, if desired, with the one material constraint of the USGA rules. Numerous alternative arrangements, bar treatments, shapes, materials, and retaining arrangements may be imagined. 
   The foregoing has described the principles, preferred embodiments and mode of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by those skilled in the art without departing from the scope of the present invention as defined by the following claims.