Patent Application
20170136302
The present invention relates to golf balls having improved aerodynamic characteristics. The improved aerodynamic characteristics are obtained through the use of specific dimple arrangements and dimple plan shapes. In particular, the present invention relates to a golf ball including at least a portion of dimples having a plan shape defined by high frequency periodic functions along a simple closed path.
Aerodynamic forces acting on a golf ball are typically resolved into orthogonal components of lift (FL) and drag (FD). Lift is defined as the aerodynamic force component acting perpendicular to the flight path. It results from a difference in pressure that is created by a distortion in the air flow that results from the back spin of the ball. Due to the back spin, the top of the ball moves with the air flow, which delays the separation to a point further aft. Conversely, the bottom of the ball moves against the air flow, moving the separation point forward. This asymmetrical separation creates an arch in the flow pattern, requiring the air over the top of the ball to move faster, and thus have lower pressure than the air underneath the ball.
Drag is defined as the aerodynamic force component acting opposite to the ball flight direction. As the ball travels through the air, the air surrounding the ball has different velocities and, thus, different pressures. The air exerts maximum pressure at the stagnation point on the front of the ball. The air then flows over the sides of the ball and has increased velocity and reduced pressure. The air separates from the surface of the ball, leaving a large turbulent flow area with low pressure, i.e., the wake. The difference between the high pressure in front of the ball and the low pressure behind the ball reduces the ball speed and acts as the primary source of drag.
Lift and drag, among other aerodynamic characteristics of a golf ball are influenced by the external surface geometry of the ball, which includes the dimples thereon. As such, the dimples on a golf ball play an important role in controlling those parameters. For example, the dimples on a golf ball create a turbulent boundary layer around the ball, i.e., the air in a thin layer adjacent to the ball flows in a turbulent manner. The turbulence energizes the boundary layer and helps it stay attached further around the ball to reduce the area of the wake. This greatly increases the pressure behind the ball and substantially reduces the drag.
Accordingly, the design variables associated with the external surface geometry of a golf ball, e.g., surface coverage, dimple pattern layout, and individual dimple geometries afford golf ball designers the ability to control and optimize ball flight. Thus far, any adjustments to dimple geometry in an attempt to optimize aerodynamic characteristics have been limited to dimple profile. In fact, while dimple profile has been used by manufacturers in an attempt to affect the aerodynamic performance of a golf ball, the dimple shape or perimeter has remained circular in nature. However, circular dimples are limited with respect to packing efficiency and number in a dimple pattern. As such, there remains a need in the art for non-circular dimple plan shapes that alter the boundary layer flow and laminar to turbulent transition and provide a means to fine tune golf ball aerodynamic characteristics by controlling the external surface geometry.
The present invention is directed to a golf ball having a generally spherical surface and including a plurality of dimples on the spherical surface, wherein at least a portion of the plurality of dimples, for example, about 50 percent or more, or about 80 percent or more, include a non-circular plan shape defined by a high frequency periodic function along a simple closed path. In one embodiment, the high frequency periodic function is a sine, cosine, sawtooth wave, triangle wave, or square wave function. In this aspect, the high frequency periodic function may be a combination of two or more periodic functions. In another embodiment, the high frequency periodic function is an arbitrary periodic function. In still another embodiment, the simple closed path is a circle, ellipse, square, or an arbitrary closed curve.
In this aspect, the plan shape is defined according to the following function:
Q(x)=Fpath(l,scl,x)*Fperiodic(s,a,p,x)
where Fpath is the path of length l, with scale factor scl, defined along the vertices x; and Fperiodic is the high frequency periodic function with sharpness factors, amplitude a, and period p defined at the vertices x. In one embodiment, the high frequency periodic function has a period, p, of about 15 to about 80, and more preferably, about 25 to about 70.
The present invention is also directed to a golf ball having a generally spherical surface and including a plurality of dimples on the surface thereof, wherein at least a portion of the plurality of dimples, for example, about 50 percent or more, or about 80 percent or more, include a plan shape defined by a high frequency periodic function along a simple closed path according to the following function:
Q(x)=Fpath(l,scl,x)*Fperiodic(s,a,p,x)
where Fpath is the path of length l, with scale factor scl, defined along the vertices x; and Fperiodic is the high frequency periodic function with sharpness factor s, amplitude a, and period p defined at the vertices x. In one embodiment, the high frequency periodic function is a sine, cosine, saw tooth wave, triangle wave, square wave, or arbitrary function. In another embodiment, the path is any simple closed path that is symmetrical about two orthogonal axes. For example, the path may be a circle, ellipse, square, or polygon. In still another embodiment, the high frequency periodic function has a period, p, of about 15 to about 80, and more preferably, about 30 to about 60. In this aspect, the high frequency periodic function may have an amplitude, a, of about 1 or less. Further, the plan shape may have an amplitude A of less than about 0.500.
The present invention is further directed to a golf ball having a surface with a plurality of recessed dimples thereon, wherein at least one of the dimples has a plan shape defined by a high frequency periodic function along a simple closed path symmetrical about two orthogonal axes according to the following function:
Q(x)=Fpath(l,scl,x)*Fperiodic(s,a,p,x)
where Fpath is a path function of length l, with scale factor scl, defined along the vertices x; and Fperiodic is a periodic function with sharpness factor s, amplitude a, and period p defined at the vertices x, wherein the periodic function is selected from a sine, cosine, sawtooth wave, triangle wave, square wave, or arbitrary function. In one embodiment, the periodic function is a sawtooth wave form, a square wave form, or a cosine wave form. In another embodiment, the plan shape may have an amplitude A of about 0.0005 inches to about 0.100 inches.
Further features and advantages of the invention can be ascertained from the following detailed description that is provided in connection with the drawings described below:
The present invention is directed to golf balls having improved aerodynamic performance due, at least in part, to the use of non-circular dimple plan shapes. In particular, the present invention is directed to a golf ball that includes at least a portion of its dimples having a plan shape defined by high frequency periodic functions along a simple closed path.
Advantageously, the dimple plan shapes produced in accordance with the present invention provide a means to fine tune the aerodynamic characteristics of a golf ball by altering the boundary layer flow and laminar to turbulent transition. In particular, the bifurcation created by the plan shape of a dimple according to the present invention creates a large transition zone on the external surface geometry, which will ultimately influence the aerodynamic behavior of a golf ball incorporating such dimples.
In addition, while not the primary goals of the dimple plan shapes of the present invention, an ancillary benefit may be improved dimple packing efficiency and uniformity of surface coverage.
The present invention contemplates dimples having a non-circular plan shape defined by high frequency, low amplitude periodic functions or linear combinations thereof along a simple closed path. In particular, golf balls formed according to the present invention include at least one dimple having a plan shape defined by high frequency, low amplitude periodic functions or linear combinations thereof along a simple closed path. By the term, “plan shape,” it is meant the shape of the perimeter of the dimple, or the demarcation between the dimple and the outer surface of the golf ball or fret surface.
According to the present invention, at least one dimple on a golf ball is formed using a simple closed path to define the dimple shape. A “simple closed path”, as used herein, includes a path that starts and ends at the same point without traversing any defining point or edge along the path more than once. For example, the present invention contemplates dimples formed using any simple cycle known in graph theory including circles and polygons. In one embodiment, the simple closed path is any simple closed path that is symmetrical about at least one orthogonal axis. In another embodiment, the simple closed path is symmetrical about two orthogonal axes. For example, the simple closed path includes a circle, ellipse, square, or polygon. In yet another embodiment, the simple closed path is an arbitrary path. In this aspect, a suitable dimple plan shape according to the present invention may be based on any path that starts and ends at the same point without intersecting any defining point or edge.
The present invention contemplates the use of periodic functions to form the dimple shape including any function that repeats its values at regular intervals or periods. For the purposes of the present invention, a function ƒ is periodic if, according to equation (1),
ƒ(x)=ƒ(x+p) (1)
for all values of x where p is the period. In particular, the present invention contemplates any periodic function that is non-constant, non-zero.
In one embodiment, the periodic function used to form the dimple shape includes a trigonometric function. Examples of trigonometric functions suitable for use in accordance with the present invention include, but are not limited to, sine and cosine.
In another embodiment, the periodic function suitable for use in accordance with the present invention includes a non-smooth periodic function. Non-limiting examples of non-smooth periodic functions suitable for use in accordance with the present invention include, but are not limited to, sawtooth wave, triangle wave, square wave, and cycloid.
In addition,
In this aspect of the invention, any of the above-mentioned periodic functions may be constructed as an infinite series of sines and cosines using Fourier series expansion for use in forming a dimple shape in accordance with the present invention. In particular, the Fourier series of a function ƒ(x), which is given by equations (2)-(5), is contemplated for use in forming a dimple shape according to the present invention:
and n=1, 2, 3 . . . .
In addition, the following Fourier series are contemplated for use in forming the dimple shape in accordance with the present invention.
For example,
In yet another embodiment, the present invention contemplates arbitrary periodic functions, or linear combinations of periodic functions for use in forming a dimple shape in accordance with the present invention. Accordingly, in one embodiment of the present invention, an arbitrary periodic function may be created using a linear combination of sines and cosines to form a dimple shape in accordance with the present invention.
According to the present invention, the plan shape of the dimple may be produced by projecting or mapping any of the above-referenced periodic functions onto the simple closed path. In general, the mathematical formula representing the projection or mapping of the periodic function onto the simple closed path is expressed as equation (6):
Q(x)=Fpath(l,scl,x)*Fperiodic(s,a,p,x) (6)
where Fpath represents the simple closed path on which the periodic function is mapped or projected with length l, with scale factor scl, defined along the vertices x; and Fperiodic is any suitable periodic function with sharpness factor s, amplitude a, and period p defined at the vertices x.
In one embodiment, the projection may be described in terms of how the periodic function alters the path function. For example, the resulting vector, Q(x), represents the altered coordinates of the path. Indeed, the “path function,” contemplated by the present invention includes any of the simple paths discussed above.
In this aspect of the invention, the resulting vector, Q(x), may also be a suitable path for a dimple plan shape according to the present invention. That is, the resulting vector, Q(x), could itself become a path to which another periodic function is mapped. Indeed, any of the periodic functions disclosed above may be mapped to the resulting vector, Q(x), to form a dimple plan shape in accordance with the present invention.
The “length,” l, and “scale factor,” scl, may vary depending on the desired size of the dimple. However, in one embodiment, the length is about 0.150 inches to about 1.400 inches. In another embodiment, the length is about 0.250 inches to about 1.200 inches. In still another embodiment, the length is about 0.500 inches to about 0.800 inches.
The variable Fperiodic of equation (6) will vary based on the desired periodic function. The term, “sharpness factor,” is a scalar value and defines the mean of the periodic function. Generally, small values of s produce periodic functions that greatly alter the plan shape, while larger values of s produce periodic functions having a diminished influence on the plan shape. Indeed, as will be apparent to one of ordinary skill in the art, once an amplitude value is chosen, the sharpness factor, s, may be varied depending on the desired amount of alteration to the plan shape. In one embodiment, the sharpness factor ranges from about 15 to about 60. In another embodiment, the sharpness factor ranges from about 18 to about 55. In still another embodiment, the sharpness factor ranges from about 20 to about 50.
The term, “amplitude,” is defined as the absolute value of the maximum distance from the path during one period of the periodic function. As shown in
In another embodiment, the plan shape amplitude, or amplitude A, of function Q(x) is related to the period p and the dimple diameter d by equation (7):
A=πd/2p (7).
For example, low amplitude periodic functions are contemplated for use in forming the dimple shape in accordance with the present invention. In one embodiment, the amplitude A is less than about 0.500. In another embodiment, the amplitude A is about 1×10−7 to about 0.100. In still another embodiment, the amplitude A is about 1×10−6 to about 0.070. In yet another embodiment, the amplitude A is about 1×10−5 to about 0.040. In still another embodiment, the amplitude A is about 0.0001 to about 0.002. For example, the amplitude A is about 0.078.
In this aspect, the amplitude A can also be expressed as the maximum distance from the path. For example, the maximum distance ranges from about 0.0001 inches to about 0.035 inches. In another embodiment, the maximum distance ranges from about 0.001 inches to about 0.020 inches. In still another embodiment, the maximum distance ranges from about 0.002 inches to about 0.010 inches. In yet another embodiment, the maximum distance ranges from about 0.003 inches to about 0.008 inches.
In this aspect, the amplitude A can also be expressed as a ratio of amplitude to effective dimple diameter. For example, the ratio of amplitude to effective dimple diameter is about 10:1 or less. In another embodiment, the ratio of amplitude to effective dimple diameter is about 7.5:1 or less. In yet another embodiment, the ratio of amplitude to effective dimple diameter is about 5:1 or less.
The “period,” p, refers to the horizontal distance required for the periodic function to complete one cycle. For example, as shown in
The period of the wave function is inversely proportional to the function frequency. Indeed, the frequency refers to the number of periods completed over the path function. For example, the frequency of a periodic function having a period p is represented by 1/p. In one embodiment, the present invention contemplates high frequency periodic functions. That is, the present invention contemplates periodic functions having a frequency of about 1/15 or less. In one embodiment, the periodic function has a frequency of about 1/25 or less. In another embodiment, the periodic function has a frequency of about 1/35 or less. In still another embodiment, the periodic function has a frequency of about 1/55 or less. In yet another embodiment, the periodic function has a frequency of about 1/70 or less. For example, the periodic function has a frequency of about 1/80.
Accordingly, by manipulating the variables of equation (6), the present invention provides for golf ball dimples having various plan shapes defined by high frequency periodic functions along simple closed paths. By using the high frequency, low amplitude periodic functions and simple closed paths disclosed herein, the present invention allows for numerous dimple plan shapes.
At step 103, the amplitude, sharpness, period, or frequency of the periodic function is selected based on the desired periodic function and path. In one embodiment, the present invention contemplates dimple plan shapes defined by a high frequency, low amplitude periodic function. Accordingly, the amplitude, sharpness, period, or frequency should be selected such that the values are in accordance with the parameters defined above.
At step 104, the variables selected above, including the path, periodic function, amplitude, sharpness, and period, are inserted into equation (6), reproduced below:
Q(x)=Fpath(l,scl,x)*Fperiodic(s,a,p,x) (6)
The resultant function is then used to project the periodic function onto the simple closed path in order to generate the dimple plan shape. The resultant function will vary based on the desired path and periodic function. For example, if the desired periodic function is a cosine function, Fperiodic may be represented by equation (8), depicted below:
f(x)=s+a*cos(p*pi*x) (8)
As discussed above, the resultant dimple plan shape (e.g., the resulting vector Q(x)) may also be used as the path to which another periodic function is mapped. For example, a periodic function having a different period or a different periodic function may be projected onto the resultant dimple plan shape to form a new dimple plan shape in accordance with the present invention.
After the dimple plan shape has been generated, at step 105, the plan shape can be used in designing geometries for dimple patterns of a golf ball. For example, the plan shape paths generated by the methods of the present invention can be imported into a CAD program and used to define dimple geometries and tool paths for fabricating tooling for golf ball manufacture. The various dimple geometries produced in accordance with the present invention can then be used in constructing a dimple pattern that maximizes surface coverage uniformity and dimple packing efficiency. The resulting dimple pattern may then be applied to the outer surface of a golf ball.
Golf ball dimple patterns using plan shapes produced in accordance with the present invention can be modified in a number of ways to alter ball flight path and the associated lift and drag characteristics. The plan shapes can be scaled and weighted according to proximity to neighboring dimples. For example, the plan shapes of the present invention may be enlarged or reduced based on the neighboring dimples in order to allow for greater dimple packing efficiency. Likewise, the profile can be ‘micro’ altered to tailor desired dimple volume, edge angle, or dimple depth to optimize flight performance.
The golf ball dimple plan shapes of the present invention may be tailored to maximize surface coverage uniformity and packing efficiency by altering the shape based on neighboring dimples. Dimples having plan shapes according to the present invention can be designed such that the dimples are packed more closely together to reduce the width of the land portions adjacent to each dimple. Thus, the dimples of the present invention allow for maximizing the dimple coverage on the surface of a golf ball by reducing the land portion located between adjacent dimples.
In one embodiment, the dimple pattern provides greater than about 80 percent surface coverage. In another embodiment, the dimple pattern provides greater than about 85 percent surface coverage. In yet another embodiment, the dimple pattern provides greater than about 90 percent surface coverage. In still another embodiment, the dimple pattern provides greater than about 92 percent surface coverage.
While the plan shapes of the present invention may be used for at least a portion of the dimples on a golf ball, it is not necessary that the plan shapes be used on every dimple of a golf ball. In general, it is preferred that a sufficient number of dimples on the ball have plan shapes according to the present invention so that the aerodynamic characteristics of the ball may be altered. For example, at least about 30 percent of the dimples on a golf ball include plan shapes according to the present invention. In another embodiment, at least about 50 percent of the dimples on a golf ball include plan shapes according to the present invention. In still another embodiment, at least about 70 percent of the dimples on a golf ball include plan shapes according to the present invention. In yet another embodiment, at least about 90 percent of the dimples on a golf ball include the plan shapes of the present invention. Indeed, 100 percent of the dimples on a golf ball may include the plan shapes of the present invention.
While the present invention is not limited by any particular dimple pattern, dimples having plan shapes according to the present invention are arranged preferably along parting lines or equatorial lines, in proximity to the poles, or along the outlines of a geodesic or polyhedron pattern. Conventional dimples, or those dimples that do not include the plan shapes of the present invention, may occupy the remaining spaces. The reverse arrangement is also suitable. Suitable dimple patterns include, but are not limited to, polyhedron-based patterns (e.g., icosahedron, octahedron, dodecahedron, icosidodecahedron, cuboctahedron, and triangular dipyramid), phyllotaxis-based patterns, spherical tiling patterns, and random arrangements.
The dimples on the golf balls of the present invention may include any width, depth, depth profile, edge angle, or edge radius and the patterns may include multitudes of dimples having different widths, depths, depth profiles, edge angles, or edge radii.
Since the plan shape perimeters of the present invention are noncircular, the plan shapes are defined by an effective dimple diameter which is twice the average radial dimension of the set of points defining the plan shape from the plan shape centroid. For example, in one embodiment, dimples according to the present invention have an effective dimple diameter within a range of about 0.005 inches to about 0.300 inches. In another embodiment, the dimples have an effective dimple diameter of about 0.020 inches to about 0.250 inches. In still another embodiment, the dimples have an effective dimple diameter of about 0.100 inches to about 0.225 inches. In yet another embodiment, the dimples have an effective dimple diameter of about 0.125 inches to about 0.200 inches.
The surface depth for dimples of the present invention is within a range of about 0.003 inches to about 0.025 inches. In one embodiment, the surface depth is about 0.005 inches to about 0.020 inches. In another embodiment, the surface depth is about 0.006 inches to about 0.017 inches.
The dimples of the present invention also have a plan shape area. By the term, “plan shape area,” it is meant the area based on a planar view of the dimple plan shape, such that the viewing plane is normal to an axis connecting the center of the golf ball to the point of the calculated surface depth. In one embodiment, dimples of the present invention have a plan shape area ranging from about 0.0025 in2 to about 0.045 in2. In another embodiment, dimples of the present invention have a plan shape area ranging from about 0.005 in2 to about 0.035 in2. In still another embodiment, dimples of the present invention have a plan shape area ranging from about 0.010 in2 to about 0.030 in2.
Further, dimples of the present invention have a dimple surface volume. By the term, “dimple surface volume,” it is meant the total volume encompassed by the dimple shape and the surface of the golf ball.
In another embodiment, dimples produced in accordance with the present invention have a plan shape area and dimple surface volume falling within the ranges shown in
Since, as discussed above, the dimple patterns useful in accordance with the present invention do not necessarily include only dimples having plan shapes as described above, other conventional dimples included in the dimple patterns may have similar dimensions.
In addition to varying the size of the dimples, the cross-sectional profile of the dimples may be varied. The cross-sectional profile of the dimples according to the present invention may be based on any known dimple profile shape. In one embodiment, the profile of the dimples corresponds to a curve. For example, the dimples of the present invention may be defined by the revolution of a catenary curve about an axis, such as that disclosed in U.S. Pat. Nos. 6,796,912 and 6,729,976, the entire disclosures of which are incorporated by reference herein. In another embodiment, the dimple profiles correspond to polynomial curves, ellipses, spherical curves, saucer-shapes, truncated cones, trigonometric, exponential, or logarithmic curves, and flattened trapezoids.
The profile of the dimple may also aid in the design of the aerodynamics of the golf ball. For example, shallow dimple depths, such as those in U.S. Pat. No. 5,566,943, the entire disclosure of which is incorporated by reference herein, may be used to obtain a golf ball with high lift and low drag coefficients. Conversely, a relatively deep dimple depth may aid in obtaining a golf ball with low lift and low drag coefficients.
The dimple profile may also be defined by combining a spherical curve and a different curve, such as a cosine curve, a frequency curve or a catenary curve, as disclosed in U.S. Patent Publication No. 2012/0165130, which is incorporated in its entirety by reference herein. Similarly, the dimple profile may be defined by a combination of two or more curves. For example, in one embodiment, the dimple profile is defined by combining a spherical curve and a different curve. In another embodiment, the dimple profile is defined by combining a cosine curve and a different curve. In still another embodiment, the dimple profile is defined by combining a frequency curve and a different curve. In yet another embodiment, the dimple profile is defined by combining a catenary curve and a different curve. In still another embodiment, the dimple profile may be defined by combining three or more different curves. In yet another embodiment, one or more of the curves may be a functionally weighted curve, as disclosed in U.S. Patent Publication No. 2013/0172123, which is incorporated in its entirety by reference herein.
The dimples of the present invention may be used with practically any type of ball construction. For instance, the golf ball may have a two-piece design, a double cover, or veneer cover construction depending on the type of performance desired of the ball. Other suitable golf ball constructions include solid, wound, liquid-filled, and/or dual cores, and multiple intermediate layers.
Different materials may be used in the construction of the golf balls made with the present invention. For example, the cover of the ball may be made of a thermoset or thermoplastic, a tastable or non-castable polyurethane and polyurea, an ionomer resin, balata, or any other suitable cover material known to those skilled in the art. Conventional and non-conventional materials may be used for forming core and intermediate layers of the ball including polybutadiene and other rubber-based core formulations, ionomer resins, highly neutralized polymers, and the like.
The following non-limiting examples demonstrate plan shapes of golf ball dimples made in accordance with the present invention. The examples are merely illustrative of the preferred embodiments of the present invention, and are not to be construed as limiting the invention, the scope of which is defined by the appended claims.
The following example illustrates golf ball dimple plan shapes defined by a high frequency cosine periodic function mapped to a circular path. Table 2, depicted below, describes the mathematical parameters used to project the periodic function onto the simple closed path.
The following example illustrates golf ball dimple plan shapes defined by a high frequency square wave periodic function mapped to a circular path. The non-uniform square wave function is approximated by a four-term Fourier series. Table 3, depicted below, describes the mathematical parameters used to project the periodic function onto the simple closed path.
The following example illustrates golf ball dimple plan shapes defined by a high frequency arbitrary periodic function mapped to an arbitrary path. The arbitrary periodic function is created using a linear combination of sines and cosines. Table 4, depicted below, describes the mathematical parameters used to project the periodic function onto the simple closed path.
The following example illustrates golf ball dimple plan shapes defined by a high frequency sawtooth wave periodic function mapped to an elliptical path. The non-uniform sawtooth wave function is approximated by a four-term Fourier series. Table 5, depicted below, describes the mathematical parameters used to project the periodic function onto the simple closed path.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used.
The invention described and claimed herein is not to be limited in scope by the specific embodiments herein disclosed, since these embodiments are intended as illustrations of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. All patents and patent applications cited in the foregoing text are expressly incorporate herein by reference in their entirety.
