Abstract:
A weight matched set of golf clubs is provided, wherein each club provides the golfer with precisely the same feel when the club is swung. Weight is added to each of the golf clubs in a set whose rotational dynamic properties (e.g., moment of inertia) have been matched about a selected axis. Sufficient weight is added to each of the clubs in the set to make the total weight of that club equal to the total weight of the heaviest club in the set. Such weight is added in such manner as to leave the moment of inertia about the selected axis of each club in the set essentially unchanged. This will provide the golfer with a set of clubs whose translational inertia, as well as the previously established rotational inertia, is essentially the same for each club in the set.

Description:
RELATED APPLICATION  
       [0001]     The present application claims priority of U.S. Patent Application Ser. No. 60/668,467 filed by Alan L. Brooks on Apr. 4, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to providing a matched set of golf clubs that all have the same feel when used by a golfer by rendering each club to have the same total weight without substantially changing the rotational dynamic properties of the clubs or the flexural properties of the shaft in each club.  
         [0004]     2. Description of Related Art  
         [0005]     The action taken by a golfer in striking the ball can be characterized as having four parts. The first part is the ‘address of the ball’ wherein a stationary position is assumed by the golfer and the club head is placed in some relation to the ball. The second part is the ‘backswing’ wherein the club is taken from the address position to a position generally above and behind the shoulders of the golfer where the club is poised to strike the ball. The third part is the ‘downswing’ where the club is used to strike the ball and the fourth part is the ‘follow through’ where the golfer and club are brought back to a stationary position following the striking of the ball.  
         [0006]     For years, golfers have tried to improve their game by searching for the ideal set of golf clubs, wherein each club ‘feels’ the same and performs in a consistent manner. As such, numerous methods have been formulated in the attempts to dynamically match a set of golf clubs. Many systems have been developed that match the dynamics of one club in a set to the dynamics of other clubs in the same set.  
         [0007]     One such method for matching the dynamics of golf clubs in a set is to provide the set with the same moment of inertia with respect to a common swinging axis. Such a method is disclosed in U.S. Pat. No. 3,698,239 issued to Everett, III. This method uses the assumption that having identical moments of inertia per club will inherently provide the golfer with better feel and more control. An attempt to provide a method for producing a set of moment of inertia matched clubs is disclosed in U.S. Pat. No. 1,953,916 issued to Adams.  
         [0008]     The commonly used “Lorythmic Swing Weight Scale” defines a ‘swing weight’, which approximates the moment of inertia about an axis at the grip end of a club. This approximation is performed by measuring the static moment about a fulcrum point which is established at a specified distance from the grip end of the club. Note that swing weight is not a measurement of the moment of inertia, but rather an estimation of the moment of inertia. Also note that swing weight is a valid approximation of moment of inertia only over a relatively narrow range of club design parameters.  
         [0009]      FIG. 1  is a diagram illustrating the manner in which the swing weight of a golf club  100  is determined. Golf club  100  includes shaft  101 , head  102  and grip  103 . The swing weight SW is determined by supporting the shaft  101  at a fulcrum point F, and measuring the moment required to statically balance the club. The fulcrum point F is located a precise distance (i.e., 14 inches) from the grip end of the club. As mentioned above, the swing weight is an approximation of the moment of inertia of the club  100  around an axis A at the grip end  104  of the club.  
         [0010]     Swing weight is expressed as a combination of a letter (A, B, C, D, E, F) and a number (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10). Each combination of letter and number is known as a ‘swing weight point’. Thus, there are 77 possible swing weight points. The lightest swing weight is AO, and the heaviest swing weight is G10. Most men&#39;s golf club sets are manufactured with a swing weight of D0 or D1, while most women&#39;s golf club sets are manufactured with a swing weight of C5 to C7. Each golf club in a set is manufactured to have the same swing weight.  
         [0011]     In order for each golf club in a set to have the same swing weight, the weight of the golf club head  102  must decrease as the length of the golf club shaft  101  increases. Successive clubs in a set typically vary in shaft length by 0.5 inches and club head weight by 7 grams, with longer clubs having a lighter head weight. For example, if a 9-iron of a set has a length of L, and a club head weight W, then the 8-iron of the same set typically has a length of L+0.5 inches and weight of W−7 grams. The total weight of successive clubs in a set varies by about 5 grams. As club head weights increase by 7 grams, the correspondingly shorter shafts decrease in weight by about 2 grams. For this reason, each of the golf clubs of a set will have a different total weight. For example, a 3-iron may weigh 30 grams less than a 9-iron from the same set. This effect is amplified for a driver (or any other wood), which typically has a longer and lighter shaft. For example, a driver having a 45.5 inch graphite (carbon composite) shaft may have a total weight of about 310 grams, which is about 130 grams lighter (about 30% lighter) than a steel shafted 9-iron of the same set. In virtually all sets of golf clubs currently produced, the weight of each individual club varies substantially from every other club in the set.  
         [0012]     With a matched swing weight, each of the golf clubs in a set will ‘feel’ similar during phases of the swing where the club head swings (i.e., rotates) about the axis A at the grip end of the shaft. The main phase of the swing where the club head swings about the grip end of the shaft exists during the final phase of the downswing, immediately before (and after) the club head makes impact with the golf ball. During this phase of the downswing, the golfer&#39;s arms are extended, and the club head swings about an axis created by the golfer&#39;s wrists. This axis point substantially coincides with the axis A at the grip end of the shaft. This phase of the downswing is hereinafter referred to as the ‘release’, because the club head is ‘released’ to swing about the wrists.  
         [0013]     However, the golf swing is a very complicated movement, which includes movements other than the above-described ‘release’ phase of the downswing. Other common movements in the golf swing include the backswing, the initial phase of the downswing and the follow-through. Swing weight is a poor approximation of how the club ‘feels’ during much of these other swing movements, because the primary movement of the club head is not a rotating movement about a fixed axis during these other swing movements. For example, during the last phase of the backswing and the initial phase of the downswing, the golf club is translated by the hands and rotates very little.  FIG. 2  illustrates one example of translational movement of golf club  100  along axis T. Unfortunately, there is a significant difference in the translational inertia (i.e., weight) of the various golf clubs in the set. For this reason, a 9-iron and a driver having the same swing weight will ‘feel’ very different during the last phase of the backswing and the initial phase of the downswing. This difference in ‘feel’ may cause golfers to apply different swings to different golf clubs of the same set. That is, the difference in ‘feel’ often causes golfers to swing the 9-iron in a different manner than they swing the driver (or other clubs of the same set). This undesirably introduces additional complexity to an already complex series of movements.  
         [0014]     As described above, swing weight matching was developed as an approximation of moment of inertia matching. Swing weight matching is more easily understood and implemented than true moment of inertia matching. Over the years, swing weight matching has become the de facto standard for club design. Consequently, it would be difficult to introduce a new set of golf clubs, wherein different golf clubs in the set exhibit different swing weights. It would also be difficult to introduce a set of golf clubs having swing weights that vary from the norm of D0 or D1 for men&#39;s clubs, or C5 to C7 for women&#39;s clubs.  
         [0015]     However, it would be desirable to have a set of golf clubs which ‘feel’ the same through a wider range of movements during the golf swing. More specifically, it would be desirable to have a set of golf clubs that all exhibit the same moment of inertia during the release phase of the downswing, and also exhibit substantially the same translational inertia during other phases of the backswing and downswing. That is, it would be desirable to have the same ‘feel’ for all clubs during larger portions of the backswing and downswing movements.  
       SUMMARY  
       [0016]     Accordingly, the present invention provides a set of golf clubs, wherein each golf club in the set exhibits substantially the same rotational moment of inertia about a fixed axis, and wherein each golf club in the set has the same translational inertia (i.e., total weight). That is, the golf clubs in the set are matched in both rotational moment of inertia and translational inertia. The present invention therefore includes the total weight of the golf club in the systematic matching of the golf clubs within a set.  
         [0017]     In accordance with one embodiment, the total weight of each golf club is matched to the weight of the heaviest golf club of the set. For example, assuming that the 9-iron is the heaviest club of the set, then weight is added to each of the other clubs in the set, such that all of the clubs of the set weigh the same as the 9-iron. In order to prevent this added weight from significantly modifying the rotational moment of inertia of the clubs, the weight is added at the axis of rotation about which the rotational moment of inertia is determined and matched, either precisely or by approximation (e.g., by swing weight). In a particular embodiment, the weight is added inside the shaft of the club, at the grip end of the club.  
         [0018]     The present invention will be more fully understood in view of the following description and drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a diagram illustrating the manner in which the swing weight of a golf club is determined.  
         [0020]      FIG. 2  is a diagram illustrating an axis of translation exhibited while swinging the golf club of  FIG. 1 .  
         [0021]      FIG. 3  is a diagram of a golf club having a weight installed in the shaft in accordance with one embodiment of the present invention, wherein the a swing weight or moment of inertia of the club is determined about an axis at the grip end of the club.  
         [0022]      FIGS. 4A and 4B  are diagrams illustrating the weight and shaft of the club of  FIG. 3  in more detail in accordance with one embodiment of the present invention.  
         [0023]      FIG. 5  is a diagram of a set of weight-matched golf clubs having a matched swing weight or moment of inertia about an axis located at the grip end of each club.  
         [0024]      FIG. 6  is a diagram of a golf club having a weight installed in the shaft in accordance with an alternate embodiment of the present invention, wherein the a swing weight or moment of inertia of the club is determined about a axis away from the grip end of the club. 
     
    
     DETAILED DESCRIPTION  
       [0025]     The present invention provides a matched set of golf clubs, wherein each club in a set of clubs, irons, woods, or a combination thereof has the same weight as other clubs in the set. This is done in a manner that minimally changes the overall moment of inertia of the club about a given axis of rotation. This can provide the golfer with a set of clubs wherein each club in the set has the same translational inertia (i.e., weight) as other clubs in the set as well as preserving the same rotational moment of inertia for all clubs in the set. This provides a more complete matching of the clubs within a set to a golfer&#39;s swing.  
         [0026]     In accordance with the present invention, weight is added at or near the location of the rotational axis about which the moment of inertia (the rotational inertia) of each club in the set has been matched. The weight is added at this location to assure that the additional moment of inertia introduced by the weight is very small compared to, and does not significantly affect, the designed moment of inertia of the golf club.  
         [0027]     The weight added is particular to each club in the set and is sufficient to bring the total weight of each club in the set up to the same desired total weight. For example, weight can be added to all but the heaviest club in the set, such that the total weight of each club is equal to the weight of the heaviest club in the set, thereby giving each club in the set the same translational inertia. Because the translational inertia (i.e., weight) of each club is matched, each club ‘feels’ the same during the last phase of the backswing and the initial phase of the downswing.  
         [0028]      FIG. 3  is a diagram of a golf club  200  in accordance with one embodiment of the present invention. Golf club  200  includes shaft  201 , club head  202 , grip  203  and weight  205 . In the absence of weight  205 , the swing weight of golf club  200  is matched with the swing weight of other clubs in the same set (not shown). Consequently, golf club  200  and the other clubs in the same set are designed to have the same approximate moment of inertia about the axis A at the grip end of club  200 . Alternatively, golf club  200  and the other clubs in the same set can be designed to have the same actual moment of inertia about the axis A. Weight  205  is affixed inside the grip end of shaft  201 , in close proximity to axis A, in accordance with one embodiment of the present invention. More specifically, weight  205  is located as close as possible to the axis of rotation about which the moment of inertia of the clubs in the set is estimated or determined. Because weight  205  is located close to the axis A, this weight  205  has a minimal effect on the rotational moment of inertia of the club  200  about this axis A.  
         [0029]      FIGS. 4A and 4B  illustrate weight  205  and shaft  201  in more detail in accordance with one embodiment of the present invention. In this embodiment, weight  205  is a cylindrical weight of stepped diameter, with a large diameter section  205 A having the same diameter as the outer diameter of the grip end of shaft  201 , and a smaller diameter section  205 B having a diameter slightly smaller than the inside diameter of the grip end of shaft  201 . The smaller diameter section  205 B is inserted into the grip end of hollow shaft  201 . An adhesive layer may be applied between the outside of smaller diameter section  205 B and the inside of shaft  201 , thereby helping to hold weight  205  in place and prevent rattling. The large diameter section  205 A extends a short distance beyond the end of the grip end of shaft  201 . The large diameter section  205 A prevents the weight  205  from slipping down the shaft  201  in the event the adhesive bond fails. Following installation of weight  205 , the grip  203  is installed over the large diameter section  205 A of the cylindrical weight and the grip end of shaft  201 . Installation as described will minimize the additional moment of inertia contributed by the additional weight, thereby leaving the moment of inertia of the club nearly at its original value.  
         [0030]     In other embodiments, weight  205  can have other shapes. For example, weight  205  can have threads which enable the weight to be screwed into the grip end of shaft  201 . In other embodiments, weight  205  may include only large diameter section  205 A or small diameter section  205 B.  
         [0031]     Weight  205  can be made of various materials, including, but not limited to, brass, aluminum, steel, lead, copper or other metals. In accordance with one embodiment, each club in the set may have a corresponding weight made of the same material. In another embodiment, different clubs in the set may have corresponding weights made of different materials. Thus, one club may have a brass weight, while another club may have an aluminum weight. In another embodiment, the weight material for each club is selected such that length of the weight used in each club of the set is substantially matched. That is, materials having different densities are used, such that each weight has the same (or approximately the same) length within each club. In another embodiment, the densest material that can be reliably fixed in the grip end of shaft  201  is used, thereby minimizing the effect the weight has on the moment of inertia of the club.  
         [0032]      FIG. 5  is a diagram illustrating a small set of golf clubs, including clubs  200 ,  300 ,  400  and  500  in accordance with one embodiment of the present invention. Club  200  has been described above in connection with  FIG. 3 . In the described example, club  200  is a driver, although this is not necessary. Clubs  300 ,  400  and  500  have shafts  301 ,  401  and  501 , respectively, club heads  302 ,  402  and  502 , respectively and grips  303 ,  403  and  503 , respectively. Club  500  is the heaviest club of the matched set. In the described example, club  500  is a 9-iron, club  400  is a 6-iron and club  300  is a 3-iron, although this is not necessary.  
         [0033]     In the described example, each of clubs  200 ,  300 ,  400  and  500  has been swing weight matched, such that each of these clubs has the same estimated moment of inertia about axis A. In another embodiment, each of clubs  200 ,  300 ,  400  and  500  may be moment of inertia matched such that each of these clubs has the same actual moment of inertia about axis A.  
         [0034]     Weights  205 ,  305  and  405  are inserted in the grip ends of shafts  201 ,  301  and  401  as illustrated. Weights  205 ,  305  and  405  are selected such that each of clubs  200 ,  300  and  400  weigh the same as club  500  (which does not include a weight). If all of the weights  205 ,  305  and  405  are made of the same material, then weight  205  will extend a greater distance into shaft  201  than weight  305  extends into shaft  301 . However, this difference in distance has a minimal impact on the rotational moment of inertia of the clubs.  
         [0035]     Note that weights  205 ,  305  and  405  will cause the swing weights of clubs  200 ,  300  and  400  to be significantly reduced (See  FIG. 1 ). Thus, while clubs  200 ,  300  and  400  may have a swing weight of D0 or D1 without weights  205 ,  305  and  405 , these clubs  200 ,  300  and  400  may have swing weights in the range of about A-3, B-8 and C-8 with weights  205 ,  305  and  405 . Moreover, weights  205 ,  305  and  405  cause clubs  200 ,  300 ,  400  and  500  to have different swing weights (but the same feel). As described above, a relatively narrow range of swing weights are acceptable within the golfing community, and the swing weights associated with the present invention are significantly outside of this range. Thus, recognition that swing weight matching is only an approximation of moment of inertia matching, and that moment of inertia matching is the underlying design goal is required to make the improvements in club design represented by the present invention possible.  
         [0036]      FIG. 6  is a diagram of a golf club  600  in accordance with an alternate embodiment of the present invention. Golf club  600  includes shaft  601 , club head  602 , grip  603  and weight  605 . Golf club  600  is part of a set of golf clubs (not shown) which have the swing weight or moment of inertia determined about an axis B, which is located away from the grip end of the shaft  601 . In this embodiment, the weight  605  is installed in the shaft  601 , such that the center of mass of the weight  605  coincides as closely as possible to axis B. Again, weight  605  is selected to bring the total weight of the club  600  up to the desired level (i.e., the weight of the heaviest club in the set).  
         [0037]     Although the invention has been described in connection with several embodiments, it is understood that this invention is not limited to the embodiments disclosed, but is capable of various modifications, which would be apparent to one of ordinary skill in the art. For example, although the present invention has described all golf clubs in a set as having the same weight, it is understood that in other embodiments, different subsets of golf clubs in the set can have different weights. For example, the long irons and woods of a set can be designed to have the same first weight, while the short irons of a set can be designed to have the same second weight, wherein the first weight is different than the second weight.  
         [0038]     In addition, although the present invention has been described all golf clubs in a set having the same weight and same moment of inertia, it is understood that some variation in weights and moments of inertia may exist within a set, wherein the set still falls within the scope of the present invention. In one embodiment, the weights of the clubs in the set and/or the moments of inertia of the clubs in the set may vary within a 10% range. Within this range, the weights of the clubs are defined as being “substantially equal”. In another embodiment, the weights of the clubs in the set and/or the moments of inertia of the clubs in the set may vary within a 5% range. In yet another embodiment, the weights of the clubs in the set and/or the moments of inertia of the clubs in the set may vary within a 1% range.