Face markings for golf clubs

Improved golf club heads indicating the location of an optimum hit point on the striking face for maximum shot distance of any hit location on the face (“maximum distance spot”, called MD) and an indication of a second optimum hit point giving best distance, with the condition of minimum or no change of torque caused feel as perceived by the golfer at impact (“best feel spot,” called BF) are disclosed. Methods to locate these optimum locations are described. It has been widely assumed and believed that these two points have the same location. The present inventors have found that this is not true. The principal application is to “wood” type golf clubs designed to hit golf balls from a tee, but can provide useful information for clubs hitting balls from the ground. The indication of MD and BF locations on the club face may take any of various forms.

BACKGROUND OF THE INVENTION

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.

PRIOR ART

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:Maximum Sweet Spot—“The Maximum Sweet Spot 16, is a point on the end of the bat offering maximum power and control for the direction of intent, that may never be facilitated because of the ball diameter.” (col. 12, lines 28-31) In reference to golf clubs, the Maximum Sweet Spot 16 is at the intersection of the Sweet Line and the sole portion of the face perimeter”.Optimum Sweet Spot—“The Optimum Sweet Spot 17, is a point on the bat that takes into regards many parameters including Swing Plane 1, Swing Plane Arc 27, and Swing Plane Radius 36, that is dependant upon the object or ball diameter, compression, etc., wherein hitting the ball square, results in optimum power and control for the direction of intent.” (col. 12, lines 32-37) It is also described as “the varying Optimum Sweet Spot 17” (col. 13, lines 14-15) as compared to a unique point on the Sweet Line.True Sweet Spot—“The True Sweet Spot is associated with clubheads designed to hit a Ball Impact Point, primarily from one reference point, such as the ground, that can be any combination of the Six Sweet Spots, or of a general independent or reference nature. The True Sweet Spot can be used to strike a ball at another height if the club lie angle is altered.” (col. 5, lines 12-17) There is no teaching in '494 or '882 that the True Sweet Spot is that spot on the Sweet Line with no feel and best distance.

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.

SUMMARY OF THE INVENTION

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.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

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 at9inFIG. 2, for which a hit anywhere along this line causes no change in acceleration of the shaft rotation and thus zero change of torque and no sudden change of twisting feel by the golfer. The line is referred to at times in this specification simply as the “no feel” line. Importantly, the present inventors discovered that for hit points along this no feel line9, there is a unique point that results in greatest distance. This is the best-feel spot or BF, as defined above. Hits elsewhere along line9give less ball travel distance and also alter the direction at which the ball is launched. There is no change of rotation or torque at impact for hits along the “no feel” line.

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 bookHow 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 robot26whose clamp for gripping the club is shown as26A (FIG. 3). Such devices are now well known and widely used by golf club designers. Briefly, the golfing robot consists of a machine with a clamp to serve as a real golfer's hands. The mechanism holds a golf club in the same way as a real golfer. It has a mechanical drive to swing the club almost exactly as a real golfer would swing. The club head path, speed of swing, wrist angle rotation rate, and other important variables modeling a golfer swing can be set to be repeatable.

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 robot26, 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 at25, 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 golfer26and the known processes of measuring direction, speed, and spin of the ball, is to add a sensor30to 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 sensor30. 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.

FIG. 3is a view toward a clubface. It illustrates a suitable sequence of hit point locations that may be made with the robot golfer indicated schematically at26. The procedure to find the point BF is to use the robot26to swing the club and strike a ball at a predetermined location and club head speed. The location of each impact point is defined by an X coordinate being the horizontal distance from the face center toward the heel of the club and a Y coordinate being the vertical distance above the sole of the club. The X and Y axes are shown inFIG. 3. At each hit location13shown inFIG. 3, the measurement of the positive or negative values of angular torque on the grip28or shaft29and the hit distance or ball travel from impact are recorded. As shown inFIG. 3, the impact locations are on several spaced apart, generally parallel lines12. The angular torque serves to indicate angular acceleration about the long axis29A of the club shaft. Lines12are nominally perpendicular to the long axis of the club shaft, but can be at a somewhat different angular position without affecting results. The lines12should be angled upwardly in direction from the heel to the toe of the club head relative to the sole27. When these measurements are made for at least 3 and preferably 4 or more different lines12with at least 3 and preferably 4 or more different hit points13on each line, the robot golfer test for determining BF is complete.

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.

Step1is to create a graph for each line12, plotting the values of shaft torque versus the X coordinate of the hit location for each point13. Next, connect the points with a best fit line and determine the X and Y (through the equation for the line12) coordinates of the point such as14where the torque or twist on the shaft29and grip28is zero.

Step2is to create similar graph for each line12plotting instead the values of hit distance versus the X coordinate of the hit location at each point13. 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 point14, the zero torque hit location found in Step1.

Step3is shown inFIG. 4, where the location of the zero-torque points14of Step1are graphed, Y coordinate versus X coordinate. Connecting these points determine a best fit line20inFIG. 4representing the no torque line.

Step4is shown inFIG. 5, where the hit distance determined in Step2is plotted against the X coordinate of point14for each line12. A best fit curve25inFIG. 5drawn through these points shows the center point for obtaining best hit (ball travel) distance, which is indicated at21inFIG. 5.

For illustration, point21determined inFIG. 5at a point along line25has been marked onFIG. 4on line20(both points have the same X coordinate value), to display the X and Y coordinates of the location of BF on the face.

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 axis29A, 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.

FIG. 1illustrates a modern, large sized, typical golf club head, numeral1. The face is indicated at2. The location of these two optimum points to center hits on the face is generally indicated by the two points3and4, where3(MD) gives maximum distance and4(BF) gives maximum distance for the condition of no or minimum torque or twisting feel as defined above. Commonly used, but sometimes omitted are score lines5. The hosel is shown at6.

FIG. 2is a view toward the face. It displays other markings where7represents the MD location. The locus of points where there is no twisting feel (zero torque) at the golfer's grip is shown as the dashed line9, and8indicates the location along this line of no-feel that gives best distance (BF). The marks or indicia are different from each other for identification.

Most golfers may prefer to hit at location3inFIG. 1or7inFIG. 2for maximum distance. Others would prefer best feel at location4or8. One reason is that, as indicated below, location4or8sacrifices only a small distance of the shot and tends to indicate to the golfer, the toe-heel location on the face where he hit.

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.

TABLE 1Results of MD and BF calculations. B3 is a large, modern club and WA is an old style,wooden head. HS is head speed, mph. MD and BF are as defined above. Distance fromface center toward heel is X and distance above the sole is Y, both in inches. Hit distanceis dist, yards. Change in angular velocity of the shaft, if it were free to turn, is dAV inrevolutions per minute. The distance (inches) between MD and BF is shown at L.HSMDBFLClub[mph]XYdistdAVXYdistdAV[in.]B3100−0.361.54257.4975.6−0.071.36254.3600.34B380−0.361.57203.3556−0.091.39201.100.32WA1000.041.08245.7277.50.191.15244.6500.17

A preferred option is to mark each of these two positions (MD and BF) as shown inFIG. 1, where one mark may be a circle, square, diamond shape or other suited mark, and the other has similarly chosen but preferably visually distinct marking such as the punch mark shown inFIG. 1. Both may be punch marks

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 inFIG. 8.

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 at35inFIG. 1to state that BF is certain distances toward the heel and downward, both relative to the maximum distance (MD) mark. Optionally, this may be done with a BF mark on the face and MD location indicated by similarly printing the distance toward the toe and upward from the BF mark. If desired the dotted line9ofFIG. 2may be marked on the clubface.FIGS. 6 and 7show other alternates for markings showing MD, BF, and representations for the line of no feel. Many other marks could be used for these indications.

FIG. 6, shows a first modified face shape of a club head35. Point MD for this club head is illustrated as a circle or dot31. The segmented line of no feel indicated as32A and32B is straight and collinear as shown and approximates the slightly curved line20ofFIG. 4. BF is indicated at34. The USGA treats face marks defining the no feel line as grooves and requires them to be straight lines.

FIG. 7shows a further modified face shape of a club head36. MD is indicated at38. The line segments40A and40B form a line that is a closer approximation of the ideal, slightly curved line20shown inFIG. 4. As shown, these segments are not collinear but extensions of these line segments intersect at BF. BF is also indicated by line segments42and line segments40A and40B, which, if continuous, cross at BF.

It is preferred and required by the USGA to conform to the Rules of Golf that the line segments40A,40B, and42as marked on the club face terminate short of the point BF and be straight, as shown inFIG. 7. Imaginary or real extensions of the marked line segments cross at BF.

FIG. 8shows another marking which identifies the location of points MD and BF. A straight line50is marked on the club face52, with one end50A of the line50locating or marking MD, and the other end50B of line50marking BF. The line50need not be straight but straight is preferred and required by the USGA to conform to the Rules of Golf. The line50provides the reference a golfer needs for identifying where the desired center hit points, MD and BF, for ball impact are located on the club face.

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.