Patent Grant
7559852
The “sweet spot” concept has long been recognized by club designers and by golfers. It is commonly marked as a circle near the center of the face. Squares or other marks are also common. This is generally considered as the spot to hit for maximum distance. A common observation in golf has been “the best feel is no feel” meaning that if there is little or no perceptible feeling of the grip twisting at the time of impact, one has hit on the sweet spot, resulting in maximum distance of the shot.
In a more detailed study, our research has shown that there is one location for a hit for maximum distance (“maximum distance spot” or MD) and another (“best-feel spot” or BF) that is generally a fraction of an inch away. BF is the location of impact for no momentary change of rotation speed of the grip nominally around the long axis of the shaft together with best distance for that condition of no change of rotational feel at the grip. The difference of distance of a shot from each of these locations is approximately 1 to 3 yards, depending on club head design, head speed at impact, and other factors. It is believed that golfers would like to know where they should try to center the impact for each case, and an indication of each of these two points is desirable. It was found that the distance of a golf shot is always less when hit at BF as compared with a hit at MD.
No prior art has been found for recognizing or indicating MD and BF. The present inventors and other club designers use modern computer programs to assist in designing golf club heads. Examples for other inventors using design programs are U.S. Patents by inventor(s) Manwaring et al: U.S. Pat. Nos. 6,431,990, 6,506,124, 6,561,917, 6,602,144, 6,821,209, and 6,929,558. Such computer code can be used or could be modified to perform the calculations required for the novel method for defining these two optimum spots. It is probable that there are various other cases of club designers using suitable computer programs. So far as is known, such methods have never been used to define these two points. When the existence of such two, unique, and optimum spots has been calculated, no known prior art shows the use of two marks on a clubface or one mark with an accompanying description of the relative location for the other location.
U.S. Pat. Nos. 6,224,494 and 6,659,882, both by Patsky, discuss methods of locating “ideal points of contact with a golf ball” also called “sweet spot” and apparently other descriptions. In '494, two references to FIG. 11 (col. 11, lines 35-37 and col. 15, line 65 to col. 16 line 9) indicate use of a “Club Torque Responder” located at the butt end of the grip. This instrument is used during dynamic clubhead impacting “to measure Sweet Line off or on hits with related derivatives and . . . ”. It further states in the paragraph starting at col. 4, line 38: “This patent encompasses new engineering design principles in golf clubs, their manufacture and fitting, applicable to alignment markings and identification at any clubhead location, on or within the clubhead, adjustable or fixed, within or external to the impact area as defined by the USGA or other entities, visual or nonvisual, color coded, blended or otherwise, singular or plurality, and in any mannerism, allowing the golfer to automatically and exactly align the clubhead to a ball at any height (emphasis added), but basically at two heights, from the Ground or perched on a Tee, whereupon at ball impact results in the transferal of optimum power, control and direction of intent.” The hit point locations on the Sweet Line at these two heights define the Ground Sweet Spot and the Tee Sweet Spot, two of five subdivides of the Infinite Sweet Spots on the Sweet Line, see Col. 5, lines 6-11. The other three subdivides on the Sweet Line are defined as:
There is no teaching in '494 or '882 instructing the golfer to tee the ball at an optimum or preferred height and make lateral adjustments to hit on the Sweet Line to result in a shot with best feel and maximum distance, which is here defined as the BF sweet spot or location.
U.S. Pat. No. 5,763,770 (McConnell et al.) describes a method of studying continuous vibrations that supposedly provides means to locate what is therein called the “sweet spot”. Their definition of “sweet spot” is not defined as the spot for maximum distance of a hit. More importantly, vibration frequency for an impact is not a single, continuing frequency of vibrations as stated in '770 but rather, is made up of a summation of many frequencies as can be defined by a Fourier analysis of impact forces that shows frequency vs. amplitude to precisely represent the impact. Also, this method does not consider the angular velocity of the head at impact resulting from golfer wrist rotation. Therefore, the sweet spot it defines is of little meaning to the golfer. The methods of the present invention use methods that are appropriately related to actual ball-club impacts and clearly relate to a “sweet spot” resulting with maximum distance (MD sweet spot) and/or a “sweet spot” resulting with best distance under the condition of minimum torsional feel (BF sweet spot), both having clear meanings as discussed herein.
U.S. Pat. No. 5,703,294 (McConnell et al.) is related to '770 in that it is based on continuous vibrations and does not define locations for MD and/or BF as defined and discussed in the present application. The '294 patent has similar shortcomings as '770 regarding club head rotation at impact resulting from golfer wrist angle rotation at impact, included in all the claimed methods here.
None of this prior art shows the novel methods claimed herein for locating BF.
A golf club head is disclosed which has a ball striking face that includes a mark at the point for which a golfer should try to center hits when seeking to maximize ball travel distance (MD) regardless of a change of twist of the club and an indication or mark at a second location when seeking best ball travel distance with “no feel” of change of twist of the club (BF).
Several suitable alternate methods for identifying these two locations are described, including using a robot golf ball striker and a computer analysis method. The first mark is for maximum distance of ball travel for any hit location on the club face as established by these methods. The second mark on the club face is a point where there is maximum ball travel and no change of twist or torque on the club shaft caused by impact, called the Best Feel or BF. The BF point can be established by computer analysis directly.
Also, using a robot golf ball striker or a live golfer, a locus of ball strike points can be established where there is no change of twist or feel of rotation of the golf club shaft and grip, which locus of points form a line on the clubface. For ball strike or hit points along this line, ball travel distance varies, but feel does not, in that the golfers perception of a momentary change of twist at the grip is at or near zero. The method then includes determining the point along the “no feel” line where ball travel distance is the maximum. BF is a unique point on this “no feel” line, where the distance of the shot is greatest, and there is no change of torque on the golf club shaft from the hit.
The abbreviations MD and BF or their names, as defined above, are used in this invention and in its claims. Unless specifically stated otherwise, the axis for terms such as torque, rotation, or twist refer to the long axis of the shaft and grip.
Humans feel quick movements such as riding in a car on a bumpy road. It is well established that the feeling is mainly a human response to changes of acceleration. (Steady acceleration does not cause the feeling, for example, the acceleration due to gravity.) This also applies to rotary motion, for example, during a golf swing, if the grip of a club is a feeling of steady angular acceleration with this acceleration suddenly altered by impact of clubface and ball, the golfer perceives this as a twisting disturbance or a change of twist, usually referred to in the following as a “change of twist” or “change of torque”, or simply “twist” or “torque”.
The present inventors determined that there exists a line on a club face that is roughly in a direction indicated by the dashed line at 9 in
At club-ball impact, there is also a small vibration that is perpendicular to the long axis of the club shaft (it would cause a tendency for the shaft to bend). This has relatively small changes in lateral acceleration of the grip and its feel is usually overshadowed by any rapid change of rotation. As a result, with respect to the feel at impact, change of rotation at impact is the important factor to be considered.
The inventors have done substantial research on the problem of where a golfer should try to center hits on the clubface. Most of this work was studied by a computer simulation program that has extensive ability to show important details of the shots resulting from any combination of a large group of design and usage variables. A further explanation of the inventors' computer program is in Chapter 2 the book How Golf Clubs Really Work and How to Optimize Their Designs, ©2000, published by Origin Inc. Also as noted in the above section on prior art, other computer programs exist, or could be modified, to have this capability.
A basic alternate to computer study to find the BF and MD points is to use a golfing robot 26 whose clamp for gripping the club is shown as 26A (
In principal, an alternate would be to use a real golfer for testing, but accuracy of that procedure would be greatly complicated by variations of the golfer's swing, measuring the torque on each hit, and other experimental factors that are not subject to control. This would require measuring of locations of hits on the face for each trial, and a more complicated process of reducing the data by statistical processes applied to a relatively large number of trials.
For the golfing robot 26, hits could be studied on a fairway, but more precise results are realized by measuring the direction, speed, and spin of the ball by electronics means using known sensors represented schematically at 25, on the club head and/or on associated equipment, after an impact by the robot golfer. Means for such measurements and for calculating distance of each hit are well known and widely used in the industry, for example as described in U.S. Pat. Nos. 5,413,345 (Nauck); 6,929,558; 6,821,209; 6,602,144, 6,561,917 and 6,431,990, (all 5 by Manwaring et al.). The teachings of these prior art patents are incorporated by reference.
For this method of finding BF, the essential addition to the robot golfer 26 and the known processes of measuring direction, speed, and spin of the ball, is to add a sensor 30 to measure torque or torsion variations at the grip that are caused by impact. A way to do this is to mount strain gages on the club shaft, preferably near the grip, that can measure torsion around the long axis of the club shaft and do so regardless of any bending of the shaft that may be present. This arrangement forms the torque sensor 30. Various known strain gage arrangements or related devices can provide this measurement of torsion. These strain gage methods and other torsion measuring devices are well known to those skilled in measuring stress and strain.
A graphical process is described below to illustrate the process of determining BF. Those skilled in data treatment will realize that this method for finding BF can be done more precisely by computer processes in place of the graphical process described. In other words, computer analysis using the recorded measurements of hit location, torque, and hit distance described above can establish the locus of points of no torque on the club shaft during a ball strike and then also determine BF along the “no feel” or no change of torque line or directly determine BF without establishing the no feel line.
Step 1 is to create a graph for each line 12, plotting the values of shaft torque versus the X coordinate of the hit location for each point 13. Next, connect the points with a best fit line and determine the X and Y (through the equation for the line 12) coordinates of the point such as 14 where the torque or twist on the shaft 29 and grip 28 is zero.
Step 2 is to create similar graph for each line 12 plotting instead the values of hit distance versus the X coordinate of the hit location at each point 13. Next, connect the points with a best fit line and determine the hit or ball travel distance at the hit location determined by the X coordinate of point 14, the zero torque hit location found in Step 1.
Step 3 is shown in
Step 4 is shown in
For illustration, point 21 determined in
BF can be determined directly by a computer analysis that models club ball impact and subsequent flight and bounce and roll of the ball combined with a numerical procedure to iterate on X and Y coordinates of hit locations on the club face. For each hit location, a linear function, which is a linear combination of shaft torque and the inverse of ball travel distance is calculated. The iteration procedure chooses the next hit location based on its criteria to minimize the linear function. The hit location minimizing this function provides the location of BF. The path of hit points tried during this process depends on the initial or starting hit point(s) specified and the details of the iteration process used.
In summary, if a hit is well toward the toe or heel, the off-center impact causes a change in rate of rotation of the head about the shaft axis 29A, loss of distance, and a direction change of the ball flight. This change of rotation rate is quickly propagated up the shaft and is readily perceived by the golfer as a twisting sensation of the grip caused by torque. This torque is measured in the present method and the series of zero torque points determined.
It is interesting to consider a strong hit that is far off the face center. If the golfer did not resist, the rotation rate would change in less than about one half millisecond by 2500 revolutions per minute or more. The golfer's grip strongly reduces this, and therefore the golfer feels a strong twisting sensation at the grip. The change of 2500 rpm rate compares to change of zero or a few revolutions per minute for hits at or very near BF or at any other point along the no feel line.
Thus, this twisting is the main factor in a golfer's feel at impact. It is an important factor that was studied in the research on where a golfer should try to center hits on a clubface.
Locating MD is simpler, well known, and widely practiced. Using robot golfer tests, it requires recording locations of a number of hits on the face and the ball travel distance for each. Either graphical or computer means can then fit the data with a 3-dimensional surface to identify the point on the face that gives maximum distance, regardless of whether there is torque on the shaft or not, which is MD. Such graphical methods are similar to the above but simpler. Another approach is using the computer analysis described in the previous paragraph using a minimizing function of the inverse ball travel distance.
In general, the research showed that hits for the BF condition should be centered a fraction of an inch toward the heel and slightly lower on the face relative to the MD position.
Most golfers may prefer to hit at location 3 in
The location of each of these two points depends on the design of the club head, such as the loft and lie angles, the location of the center of gravity and the inertia matrix terms. The locations also vary somewhat with the head speed generated by the golfer and other golfer variables. Results caused by such design and golfer variables are illustrated by differences shown when all of the figures are compared with one another and with Table 1 (discussed below).
Examples of these locations are shown in Table 1. These examples are based on having optimized (ideal) loft angle and consistent swings with the same head velocity or speed for each case. Table 1 shows that shot distance, “dist”, is slightly reduced in every case if BF is the chosen hit location over the MD location.
A preferred option is to mark each of these two positions (MD and BF) as shown in
A second option is to mark a line, one end of which defines hit location for MD and the other end locates BF as shown in
An industry standard is for the face mark to be within a 0.375 inch square. This limits some of these options. For example if the separation, L, is 0.32 or 0.34 inches for Table 1, small marks would fit within the 0.375 inch square. However if the marks for MD and/or BF are large, parts of the marks would not fit within the square. Other head designs may have larger values of the separation between MD and BF (L, see table above).
A third option is to mark on the face, one of the locations such as the MD. In this case, a second mark for BF is not made on the face. Instead, it is defined by printing instructions for locating BF such as on the top of the club head shown at 35 in
It is preferred and required by the USGA to conform to the Rules of Golf that the line segments 40A, 40B, and 42 as marked on the club face terminate short of the point BF and be straight, as shown in
The above discussion is for the clubs used to hit a ball from a tee. A golfer should tee the ball at an appropriate height so his/her average or mean impact height on the face lies at approximately the height of MD or BF above the sole. For irons and fairway woods not hitting a ball from a tee, the same calculations can be made. For such case, MD may be in a satisfactory location on the face for long irons with low loft angle. For irons with high loft angles, it will be too high on the face with the result that the club sole would be required to be deep into the turf in order to hit the MD point. Similarly, BF may also be too high for the most lofted clubs. For a designer, calculation of these points can be useful as design targets. If they cannot be reached, the designer can come as near as practical. For these clubs, maximum distance is not of concern.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
This application refers to and claims priority on U.S. Provisional Patent Application Ser. No. 60/840,565, filed Aug. 28, 2006, which application is incorporated by reference.
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