Patent Grant
6991561
The present invention is directed to a golf ball having a controlled variable moment of inertia. Particularly, the golf ball includes at least one hollow channel. At least one movable weight is located in the hollow channel near the center of the golf ball at rest, and moves outwardly as the spin rate of the ball increases. The movable weight returns towards the center of the golf ball as the spin rate decreases. The change in the radial position of the movable weight alters the moment of rotational inertia of the ball. The position of the weight within the channel is controlled, such as by a spring or spring-like device, magnetic force, etc. The present invention is also directed to a method for making a golf ball having a controlled variable moment of inertia.
Moment of inertia is the sum of the products formed by multiplying the mass of each part of an assembly by the square of its distance from a specified axis plus the moment of inertia of each part about its own center of mass. It is also sometimes referenced as rotational inertia. In spherical objects, such as a golf ball, a low moment of inertia means that a larger portion of its mass is concentrated in the center. In turn, a high moment of inertia means that more of its mass is concentrated towards the outer cover or periphery of the sphere or ball.
Moment of inertia (“MOI”) affects the playability of a golf ball in many ways. For example, moment of inertia affects the amount of spin produced when the golf ball is struck with a wood or iron. This may result in a desirable characteristic (i.e. high spin for ball placement, low spin for enhanced distance, etc.) or an undesirable characteristic (i.e. hooking or slicing, etc.) depending upon the skill level of the golfer, the type of club used, etc. Moment of inertia also affects the overall trajectory of a ball and thus, often the overall distance the ball will travel. Also, moment of inertia affects the short game, including lofting, pitching, chipping, and putting.
For some aspects of the golf game, it is desirable to have a golf ball that exhibits a relatively high moment of rotational inertia, for example in which the mass of the ball located near the outer periphery of the ball is greater than the mass of the ball located near the center of the ball. A golf ball exhibiting a high moment of inertia generally has a reduced rate of spin, including reduced side spin, so that such a ball may be desired for certain shots requiring distance. A low spin ball also produces less side spin, thus reducing the amount of hooking and slicing.
Although a golf ball exhibiting a relatively high moment of inertia has certain desirable properties at different club head speeds and with different lofted clubs, it may also possess undesirable characteristics. Furthermore, such a ball may lack the necessary feel and roll characteristics for the short game, particularly putting.
Therefore, for certain aspects of the golf game, it would be desirable for a golf ball to exhibit a relatively low moment of inertia, where the mass of the ball near the center of the ball is greater than the mass of the ball near the outer portion of the ball. As noted, in some applications, a golf ball exhibiting a relatively low moment of inertia is desirable, such as for the short game where high spin allows a skilled golfer to more easily position his/her ball on the green, etc. In turn, it is also desirable in certain situations for a golf ball to exhibit a relatively high moment of inertia, such as for the long game where enhanced distance is desirable.
Currently, golf balls having a relatively low or high fixed moment of inertia are commercially available or are known in the art. For example, U.S. Pat. No. 5,026,067 teaches a golf ball having a cover or intermediate layer with a specific gravity greater than the center, giving the golf ball a relatively high moment of inertia. Also, U.S. Pat. No. 6,010,912 teaches a golf ball having a low specific gravity core and a high specific gravity layer surrounding the core so that the golf ball has a relatively high moment of inertia. Conversely, U.S. Pat. No. 6,180,722 teaches a golf ball having a specific gravity near the center of the ball greater than the layer surrounding the center so that such a ball has a relatively low moment of inertia.
Players, depending upon their skill and preferences relating to the features of a golf ball, may choose a golf ball having a relatively high moment of inertia in order to increase distance and/or reduce the amount of slicing or hooking when driving, or a golf ball having a relatively low moment of inertia for improved feel, placement, etc., near or on the green. Unfortunately, a golfer choosing either a high or low moment of inertia golf ball in order to promote certain aspects of the game risks suffering deficiencies in other aspects of the game.
In the past, golf and/or game balls have been formed where the movement of inertia of the ball randomly varies. U.S. Pat. No. 1,120,757 discloses a game ball having a spherical ball that randomly moves within the chambers of the game ball when the game ball rotates. The springs described in that patent are used to ensure that the spherical ball does not maintain a position near the outer periphery of the game ball. That is, the springs cause the spherical ball to rebound from the outer periphery of the game ball toward the center of the game ball, thereby preventing the spherical ball from remaining in one chamber while the game ball is in action. The design of the game ball in the '757 patent causes the center of gravity, also known as the center of mass, of the game ball to randomly vary as the game ball rotates as a result of the random movement of the spherical ball within the interior of the game ball. This design causes peculiar gyration and movement of the game ball along paths that are impossible to determine with any degree of accuracy.
U.S. Pat. Nos. 728,311; 737,032; and 2,859,968 are directed to various balls that have a hollow portion in the center of the ball and one or more smaller balls within the hollow portion. When the ball rotates, the smaller ball or balls in the hollow portion freely moves in an uncontrolled fashion within the ball. None of the balls disclosed in these patents has a controlled variable moment of inertia which would maximize the playability and feel desired in a golf ball.
Accordingly, it would be useful to develop a golf ball having a controlled variable moment of inertia such that the golf ball exhibits low moment of inertia properties that are desirable during short distance play and also exhibits high moment of inertia properties that are desirable during longer distance play. In particular, it would be desirable to provide a golf ball having a moment of rotational inertia that may be selectively varied. It would also be desirable to provide a golf ball that has excellent durability.
Accordingly, it is a feature of the present invention to provide a golf ball having a controlled variable moment of inertia. In a first aspect of the present invention, a golf ball is provided which has at least one hollow channel. At least one end of the hollow channel is located along the outer periphery of the ball. At least one movable weight is located in the hollow channel. A positioning member such as a spring, which is in constant contact with the movable weight, controls the movement and position of the weight within the hollow channel. A plug encloses the end of the hollow channel along the outer edge of the ball. The golf ball is preferably formed from a material that has excellent durability.
In a second aspect, the present invention provides a golf ball comprising a core defining at least one hollow channel. The hollow channel has at least one end at the outer edge of the core. At least one movable weight comprising a magnet is located in the hollow channel. A plug also comprising a magnet encloses the end of the hollow channel at the outer edge of the core. The magnetic polarity of the end or face of the movable weight nearest the plug is the same as the portion of the plug nearest the weight. The golf ball is preferably formed from a material that has excellent durability.
In another aspect, the present invention provides a golf ball having a core defining at least one hollow channel. The hollow channel has at least one end at the outer edge of the core. At least one movable weight and a spring in continuous contact with the weight are located in the hollow channel. A plug encloses the end of the hollow channel at the outer edge of the core. The movable weight is positioned between the spring and plug. The golf ball is preferably formed from a material that has excellent durability.
In an additional aspect, the present invention provides a golf ball having a moment of rotational inertia that changes depending upon the spin rate of the ball. The golf ball preferably comprises a generally spherical core which defines one or more radially extending channels within the interior of the core. The ball further preferably comprises one or more spherical components, each positioned and movable within a respective channel. The ball also comprises one or more springs, each also positioned in a respective channel and in continuous contact with a corresponding spherical component. Upon sufficient rotation of the ball, each of the spherical components is displaced radially outward within a corresponding channel, thereby altering the moment of rotational inertia of the ball. The golf ball is preferably formed from a material that has excellent durability.
In a further aspect, the present invention provides one or more methods for promoting particular types of spin to a golf ball. In these techniques, a golf ball according to the present invention is positioned on a hitting surface such as a golf tee so that particular interior components of the ball are oriented in either a generally horizontal or vertical plane.
In yet another aspect, the present invention provides a method for making a golf ball having a controlled variable moment of inertia. The method includes preparing a ball; drilling into the ball from the outer edge to form at least one hollow channel; inserting at least one movable weight into the hollow channel; inserting a spring into the hollow channel that is in continuous contact with the weight; and enclosing the end of the hollow channel at the outer edge of the ball with a plug.
These and other objects and features of the invention will be apparent from the detailed description set forth below.
The present invention will become more fully understood from the detailed description given below and the accompanying drawings. The description and drawings are given by way of illustration only, and thus do not limit the present invention.
Generally, the preferred embodiment in accordance with the present invention is a golf ball having at least one hollow channel radially extending between the center and the outer edge or periphery of the ball, at least one movable weight located in the hollow channel, and a plug enclosing the end of the channel at the outer edge of the ball. The movement or position of the movable weight within the channel is controlled by a positioning means or member, such as a spring or by a magnetic force. At rest, the positioning member maintains the position of the movable weight toward the center of the ball.
Preferably, the positioning member is a mechanical spring. Such a spring is generally an elastic, stressed, stored-energy machine element that, when released, will recover its basic form or position. Force applied to a spring member causes it to deflect through a certain displacement thus absorbing energy. Mechanical springs can be manufactured to various amounts of force needed for displacement.
The spring utilized in the present invention is preferably a helical or a spiral spring made from any elastic material to produce the displacement force desired. The springs are oriented to return the displaced moveable weights to their original position. Different tensioned springs can be utilized in the invention depending upon the number of channels utilized, the mass of the moveable weight, the amount of centrifugal force desired to be overcome, etc.
In this regard, upon striking or hitting the ball of the present invention with a golf club, spin is imparted to the ball. Spinning of the ball causes the movable weight to move radially outward toward the periphery of the ball. Such spinning causes the weight to exert centrifugal force on the positioning member, such as the spring, thereby either compressing or tensioning the spring, depending upon the relative location of the spring to the weight and the spring constant of the positioning member.
Specifically, as the movable weight moves toward the outer region of the ball, the moment of rotational inertia of the ball increases and the positioning member becomes compressed or tensioned. As the spin rate of the golf ball decreases, the positioning member forces the movable weight to return toward the center of the ball, thereby decreasing the moment of inertia. The positioning member, such as the spring or spring-like device that is in continuous contact with the movable weight is employed to return the movable weight toward or near the center of the ball once the force of the spring is greater than the centrifugal force. Alternatively, the movable weight and plug comprise magnets that are oriented with respect to each other such that opposing magnetic poles maintain or return the movable weight near the center of the ball upon a sufficiently low centrifugal force. Further positioning means or members may also be utilized to position the movable weight member near the center of the ball upon a sufficiently predetermined low centrifugal force. The golf ball may be a one-piece golf ball, a two-piece golf ball, or a multi-layer golf ball.
A significant advantage of a golf ball having a controlled variable moment of inertia is that when the golf ball is at rest or spinning slowly, it has a relatively low moment of inertia, thereby enabling the ball to roll easily. Upon relatively large impact hits with high club head speed, such as with a driver or certain irons, the ball reaches a sufficient minimum spin rate. At that time, the centrifugal force causes the movable weights to overcome the set spring constant of the positioning members. The moveable weights are then radially and outwardly displaced within their respective channels, thereby increasing the moment of inertia of the ball. A golf ball having a relatively high moment of inertia has less spin, resulting in less hooking or slicing and/or longer overall distance. It will be appreciated that the terms “moment of rotational inertia” and “moment of inertia” are used interchangeably herein unless noted otherwise.
As the centrifugal force decreases, the positioning members force the movable weights back to their original placement in the channels. That is, when the spring force of the positioning members becomes greater than the centrifugal force, the movable weights start moving back to their original positions thereby again reducing the moment of inertia of the ball.
A mathematical model can be developed to describe the relationship between golf ball spin rate and the position of the moveable weight. In addition, there is a relationship for mass moment of inertia as a function of spin rate.
A spring resists deflection with a force proportional to the deflection from its free or unloaded height. The constant of proportionality is called the spring constant, K. Therefore, the force is shown in equation 1:
F=K·X (1)
In equation 1, F is force, K is the spring constant, and X is the deflection from free height or change in spring length. In general, an unloaded spring with no external forces acting upon it, has a free height of Hf. When the spring is loaded with force F, the height is changed to a new height H (see
X=H−Hf (2)
Since, F=K·X, and X=H−Hf, then
F=K·[H−Hf] (3)
From the above, when H=Hf, F=0 and the spring force is zero; when H<Hf, then F<0 and the force is negative or compressive; and when H>Hf, then F>0 and the force is positive or tensile.
When the golf ball is at rest (no spin), a slight preload compressive force is applied to the moveable weight. This preload force prevents any undesirable free rattle of the moveable weight. The preload force is applied by selecting the combined length of the spring and the moveable weight to be greater than the depth of the channel in which they will be installed. See
When the spring is compressed such that all of its coils are touching each other with no space in between, this is called the spring's solid height. The solid height is the minimum height that the spring can be compressed and still recover without permanent deformation. See
For any position R that the moveable weight may occupy between the resting position, R1, and the solid height, R2, the spring force can be determined as follows. See
H=Ro−R−D/2 (4)
Substituting equation (4) into equation (3) yields (5) below.
X=Ro−R−D/2−Hf (5)
Since F=K·X, substitution of (5) yields (6) below.
F=K·[Ro−R−D/2−Hf] (6)
When the golf ball is at rest (no spin), a slight preload compressive force is applied to the moveable weight. This preload force F1 can be determined by using the same methodology used in deriving equations 3 through 6 for the general case. See
X1=H1−Hf (7)
Based on
H=Ro−R1−D/2 (8)
Substituting (8) into equation (7) yields (9) below.
X1=Ro−R1−D/2−Hf (9)
Again, since F1=K·X1, then
F1=K·[Ro−R1−D/2−Hf] (10)
When the spring is compressed such that all of its coils are touching each other with no space in between, this is called the spring's solid height. The solid height force F2 can be determined by using the same methodology used in deriving equations 3 through 6 for the general case, discussed above. See
X2=H2−Hf (11)
and, based on
H2=Ro−R2−D/2 (12)
Then, substituting (12) into (11) above yields (13), below.
X2=Ro−R2−D/2−Hf (13)
Once again, since F2=K·X2, then
F2=K·[Ro−R2−D/2−Hf] (14)
Since the solid height of a spring is a dependent only upon the spring wire diameter, the number of coils in the spring and the end conditions (i.e. ground flat), this is a physical dimension of the spring. The solid height of the spring is often specified by the spring manufacturer.
H2=Hs (15)
Then, substituting (15) and (11) into (14) above yields (16), below.
F2=K·[Hs−Hf] (16)
When the golf ball is spinning in the plane that includes the moveable weights, there are two forces acting on the moveable weight. The forces are the spring force and the centrifugal force generated by the spin. The frictional forces between the moveable weight and the channel walls and the force of gravity are small compared to the spring force and the centrifugal force. The transient vibrations that result from the impact of the golf club and ball are also ignored. Equilibrium is defined here as a steady state condition when the two primary forces are equal.
Since the forces acting on the moveable weight must be in equilibrium at all times, the compressive spring force must be equal to the centrifugal force at all times. See
Fc=Fs (17)
For any position, R, that the moveable weight may occupy between the resting position, R1 and the solid height, R2, the condition of equilibrium can be applied. The spring force for this general condition was determined in (6), discussed above. The centrifugal force can be found as follows:
Fc=m a (18)
and
a=R ω2 (19)
Substituting (19) into (18) yields (20), below.
Fc=m R ω2 (20)
In the above equations, Fs spring force when the moveable weight is at position R; Fc is the centrifugal force when the core is spinning at ω and the moveable weight is at position R; R is the distance from the center of the golf ball to the center of the moveable weight in any position between R1 & R2; R1 is the distance from the center of the golf ball to the center of the moveable weight in the resting position; R2 is the distance from the center of the golf ball to the center of the moveable weight in the solid height position; Hf is the free height of the spring (unloaded); Ro is the distance from the center of the golf ball to the plugged outer end of the channel; D is the moveable weight diameter (or length);
a is the centrifugal acceleration of the moveable weight due to the spin rate ω;
m is the mass of moveable weight; and ω is the spin rate of core.
Substituting (20) and (6) into (17) above yields (21), below.
m Rω2=K·[Ro−R−D/2−Hf] (21)
Then, solving for ω in (21), yields (22) below.
ω=(K·(Ro−R−D/2−Hf)/m R)1/2 (22)
Equation (22) can be utilized to find the spin rate that causes the moveable weight to overcome the spring preload force and begin to travel in a radial direction, outward from the center of the core. Substituting R1 into (22) reveals the spin rate ω1 at which the moveable weights start to move from position R1 as shown in (23) below:
ω1=(K·(Ro−R1−D/2−Hf)/m R1)1/2 (23)
Note that when ω≦ω1, the moveable weight is pressed against the end of the channel by the preload force because the centrifugal force is less than the spring preload force. Equation (22) can also be utilized to find the spin rate that causes the moveable weight to compress the spring to its solid height. Substituting R2 into (22) reveals the spin rate ω2 at which the moveable has moved to position R2 as shown below in (24).
ω2=(K·(Ro−R2−D/2−Hf)/m R2)1/2 (24)
Note that when ω≧ω2, the moveable weight can travel no further outward because the centrifugal force has compressed the spring to its minimum height. The centrifugal force is greater than the spring force at solid height. For spin rates greater than ω1 (the spin rate required to overcome the spring preload force) but less than ω2 (the spin rate required to compress the spring to its solid height) the moveable weight will be located between R1 and R2 Its exact position is determined by the spin rate. For ω1<ω<ω2, the position of the moveable weight can be found by solving for R in equation (22), as shown below in (25).
R=K·(Ro−D/2−Hf0)/(m ω2+K) (25)
The mass moment of inertia can be determined for any position of the moveable weight. Assume that the mass moment of inertia of the completed ball or core with the moveable weights in the resting position R1 is measured to be I1. The mass moment of inertia of the ball can be determined for N moveable weights at any position R. Since the mass moment of inertia of the moveable weight about its center of mass does not change when it moves from position R1 to any position R, the only change in mass moment of inertia comes from the motion of its center of mass.
For R1<R<R2,
I=I1+N m(R2−R12) (26)
where N is the number of moveable weights; m is the mass of moveable weight; I1 is the mass moment of inertia of the completed ball or core when the moveable weights in the resting position R1; and I is the mass moment of inertia of the completed ball or core when the moveable weights in any position R such that R1<R<R2.
Equation (26) shows the minimum mass moment of inertia to be I1, which occurs when the ball is at rest and the moveable weights are located at R1. This also occurs whenever ω≦ω1. Further examination of equation (26) reveals that the maximum mass moment of inertia is I2, which occurs when the moveable weights are located at R2. This also occurs whenever ω≧ω2. While equation (26) is an expression of mass moment of inertia as a function of the position of the moveable weights, substituting (25) into (26) provides an expression for finding mass moment of inertia as a function of spin rate ω, as shown by (27) below.
I=I1+N m((K·(Ro−D/2−Hf)/(m ω2+K))2−R12) (27)
The following figures illustrate the preferred embodiment golf balls of the present invention.
Before turning attention to additional features and aspects of the preferred embodiment golf balls, it is instructive to consider the physics of imparting spin to a golf ball. First, it is a basic fact that once a golf ball is struck, there is nothing more that a golfer can do to affect the flight of the ball. For almost all golf shots, the time between a club face first striking the ball to the point at which the ball springs completely clear of the club face and into flight is about one-half of a millisecond.
As most golfers are well aware, the spin that is imparted to a golf ball affects its flight, i.e. its trajectory. And so, by controlling the spin of a ball, a golfer can control, to a limited extent, certain aspects of the ball's flight.
Upon hitting a ball, it is rare that the ball exhibits pure backspin (rotation about a horizontal axis while in flight) or pure sidespin (rotation about a vertical axis while in flight). Instead, the actual spin of a ball during flight is a combination of these spin characteristics. As a result, during flight a golf ball will typically spin about a tilted axis or an axis that is oriented at some angle. These characteristics of spin are considered in greater detail below.
The core used in the preferred embodiment golf balls defines one or more hollow channels. Although one hollow channel may be used in the core, more than one hollow channel is desired for better balance and better overall durability. Generally, it is preferred that each channel extend radially outward from the center of the core toward the outer periphery of the core. It is also preferred that each channel extend straight and not contain any bends or arcuate portions. However, it is contemplated that the present invention golf ball could encompass a core configuration using nonlinear interior hollow channels within which are disposed appropriate movable weights and springs as described herein. Also, when a plurality of hollow channels are defined by the core, the ends of the hollow channel near the center of the core are preferably not in communication with another hollow channel. As a result, it is preferred that each hollow channel is separate from the others. However, the present invention includes the use of a core having radially and oppositely directed channels that are in communication with each other.
It is also preferred that each of the hollow channels extend within the same plane and that the channels be equally spaced from one another. This same or common plane aspect is described in greater detail below. Equidistant spacing between adjacent channels extending in a common plane is determined by dividing 360° by the number of channels. For instance, if three channels are used, it is most preferred that each channel be spaced from the others by 120°. If five channels are used, it is most preferred that each channel be spaced from the others by 72°.
When a core defines a plurality of hollow channels, the hollow channels preferably extend along a common plane. That is, although the channels extend radially outward from the center of the core, the channels preferably all extend within a common plane. This unique configuration imparts to the ball a stabilizing gyroscopic characteristic. This characteristic is described in greater detail below. When the plurality of hollow channels are defined and extend along a single plane, as shown in
The unique geometric aspects of the preferred embodiment golf balls may be further understood by reference to
Regardless of how the ball is placed on the tee, the ball will seek and find the same horizontal axis each time after leaving the club face. The extended weights rotate around the horizontal spin axis perpendicular to the flight path.
It may be beneficial to know the location of the internal weights and channels within the golf ball. If the weights are as shown in
In order to facilitate properly orienting the ball on a putting green or a tee, the preferred embodiment golf balls of the present invention may also include markings or other visible indicia on the outer cover of the ball to denote the orientation of the channels within the core, i.e. the orientation of plane P. Alternatively or in addition, the preferred embodiment golf balls may include a marking to reveal the orientation of axis Aur.
Although the preferred embodiment golf balls of the present invention preferably utilize a plurality of channels that generally extend within a common, single plane, the present invention also encompasses embodiments in which one or more channels extend in two or more planes. For instance, a core configuration having six (6) channels is contemplated in which each channel is equidistant from adjacent channels and generally perpendicular to adjacent channels. A golf ball utilizing this embodiment would generally not favor a particular orientation or axis of rotation during spinning. This may be desirable for certain applications.
The cross sectional shape of the hollow channel defined within the core may vary. Preferably, the hollow channel is generally cylindrical. Alternatively, the hollow channel may be in the form of nearly any shape, such as rectangular, pentangular, etc. It is preferred that all channels utilized in a core have the same cross sectional shape.
The hollow channel may also have any length within the core. Preferably, the hollow channel extends between the outer edge or periphery of the core to near the center of the core, as shown in
The end of the hollow channel at the outer edge of the core can have a width or span equal to, less than, or greater than the width or span of the hollow channel at any location between the ends.
The shoulder can have a variety of shapes. The shoulder preferably has a circular cross sectional configuration with either cylindrical or conical sidewalls extending between the channel and the outer surface of the core.
Although it is preferred that the width or interior span of the channel be generally uniform across the length of the channel, it is possible that the width may be non-uniform. For instance, the present invention includes embodiments in which the width or interior span of the ends of the channel vary. The width or span of the end of the hollow channel near the center of the core is generally equal to or less than the width or span of the hollow channel between the ends. However, it will be appreciated that the width or span of the end of the hollow channel near the center of the core can be greater than the width or span of the hollow channel between the ends. It is preferred that the end of the hollow channel near the center of the core have a width equal to or less than the width of the hollow channel between the ends.
The hollow channel preferably has a uniform width or span, as measured between the ends, of no greater than about 1.0 inches. Preferably, the hollow channel has a width between the ends of from about 0.10 inches to about 0.50 inches. Most preferably, the hollow channel has a width of about 0.25 inches. The width of the hollow channel may vary depending on the number of hollow channels within a core, the size of the movable weights, etc. Generally, the greater the number of hollow channels in the core, the smaller the width of each channel.
The hollow channel is preferably formed by drilling from the outer edge of the core inwardly to near the center of the core or through the core to a second outer edge. Typically, when a hollow channel is drilled or otherwise formed so that the end of the hollow channel is near the center of the core, that end has a width equal to or less than the width of the hollow channel between the ends. Also, a shoulder at the end of the hollow channel at the outer edge of the core can be formed during drilling by use of a countersink or counterbore drill bit. Alternatively, two core halves may be formed by molding such that each half contains recesses so that when the two halves are placed together, a core having one or more hollow channels and shoulders is formed. The channels may also be “molded in” using retractable non-stick coated pins (i.e., Teflon® coated) in the mold cavity. The pins are retracted after the core is cured, forming hollow channels inside the core.
At least one movable weight is located within the hollow channel. The movable weight is formed from a variety of metallic or non-metallic materials. The material used in forming the movable weight preferably has a mass approximately equivalent to the mass lost when the hollow channel is formed within the core in order to maintain the desired overall mass of the golf ball. The movable weight is preferably formed of a material and has a particular shape and size in order to minimize the friction between the movable weight and the interior walls of the hollow channel so that the weight may freely move through the channel as the golf ball undergoes various rates of spin. The movable weight is typically formed from a material having a relatively high specific gravity, although the specific gravity can vary depending on the desired change in moment of inertia upon displacement of the movable weights. Preferably, the weight is formed of a metallic material. Metallic materials which may be used as the weight include, but are not limited to brass, steel, iron, tungsten, copper and nickel, etc.
The movable weight may have any size or shape as long as the weight can be inserted into the hollow channel and can readily move along the length of the hollow channel, or that portion of length permitted by the springs or other components. Shapes for the movable weight include spherical, cylindrical, or any other geometric shape desired. Spherical shaped moving weights are shown in
The movable weight may comprise a magnet.
When the golf balls 90, 100 and 110, are at rest, the magnetic movable weight and corresponding plug repel one another due to their same magnetic polarity, thereby controlling the movement or position of the movable weights. When the ball is struck and achieves a sufficient minimal spin rate, the resulting centrifugal force moves the magnetic movable weights outwardly towards the corresponding plug until the weight either comes into contact with the magnetic plug or the force of the repulsion between the magnetic weight and magnetic plug is greater than the centrifugal force. As the spin rate of the golf ball decreases, the repulsion force between the plug and weight is greater than the centrifugal force at that relatively slower spin rate so that the weight returns towards the center of the core.
Yet another embodiment involves using the magnetic force between two movable weights to attract the weights toward one another while the ball is at rest. Upon rotation of the ball, the centrifugal force urges each of the two movable weights radially outward. Preferably, such embodiment would utilize the ball structure illustrated in
The golf balls in
Although
As noted, the preferred embodiment golf balls of the present invention further include a spring or spring-like device disposed in each hollow channel. Depending on the orientation of the spring relative to the movable weight, the spring compresses or expands, i.e. tensions, as the movable weight extends outwardly once the golf ball achieves a particular spin rate. The end of the spring nearest the movable weight is in continuous contact with the weight. As shown in
The spring constant (also known as the spring rate or spring tension) of the spring or spring-like device can vary. A spring with a higher spring constant will require a greater spin rate, and thus, a greater centrifugal force for the movable weight to move outwardly as compared to a spring with a relatively lower spring constant. Likewise, a spring having a lower spring constant requires a relatively lower spin rate, and thus, a lower centrifugal force for the movable weight to move outwardly. Therefore, the spring constant or spring rate may be selected in order to adjust the minimal spin rate at which the movable weight extends radially outward toward the outer periphery of the golf ball.
Specifically, the spring constant is selected so that little or no movement of the springs and movable weights occur when the golf ball is undergoing minor movement, such as during putting. The spring constant may be increased, for example, to prevent the movement of the movable weight when struck with drivers and fairway woods, but yet allow the weights to move outwardly when struck with irons that produce a much higher spin rate than drivers and fairway woods. Golf balls of the present invention can be designed to allow the weights to move outwardly at desired minimal golf ball spin rates such as 1000 rpm, 3000 rpm, 5,000 rpm, 8000 rpm, etc.
Springs may be formed of any material which would allow the spring to compress and depress during changes in spin rate of the ball. Preferably, the springs are formed of a metallic material, such as steel. Also, the spring can be any type of spring known in the art. Preferably, the spring is a coil spring. Also, depending on the orientation of the spring relative to the movable weight within the hollow channel, a spring may be a tension spring, a compression spring or exhibit the properties of both a tension spring and compression spring.
Springs of various lengths, widths, loads, and weights may be used in order to allow the movable weights to move at lower or higher spin rates. Generally, springs having a lower stiffness (softer springs) allow the movable weights to move toward the outer edge of the core at a lower spin rate when struck with a golf club, thereby allowing a golf ball to exhibit an increased moment of inertia at a relatively low spin rate. Alternatively, springs having a higher stiffness (harder springs) allow the movable weights to move towards the outer edge of the core at a higher spin rate, thereby allowing the golf ball to exhibit an increased moment of inertia at a relatively higher spin rate.
The spring can be positioned near the center of the core so that the movable weight is between the spring and plug.
The spring may be connected to the movable weight. When the weight is positioned between a spring and a plug, as in
A plug or disk preferably encloses the end or ends of a hollow channel at the outer edge of the core. A cover may also be molded over the hollow channel.
The plug or disk may further include at least one metallic mesh or screen. The metallic mesh or screen provides additional support to the plug. The mesh may be located near the edge of the plug or near the center of the plug.
The mesh may be included in the plug composition before curing so that the mesh is located within the plug once the plug cures, or may be included on one or more of the outer edges of the plug. The metallic mesh may be formed of any metallic material. Preferably, the metallic mesh is an aluminum mesh. The plug may be formed of other materials, such as metals, rubbers, elastomers, nylons, thermoplastics, and any other suitable material desired.
Preferably, the plugs or disks have a relatively high specific gravity in order to counterbalance the overall weight of the ball. The specific gravity of the plug may be increased by a filler. The preferred fillers for use with the plug are relatively inexpensive and heavy and serve to lower the cost of the ball and to increase the weight of the ball to closely approach the USGA® weight limit of 1.620 ounces. Exemplary fillers for use in the plug are those known in the golf ball manufacturing art, and they include mineral fillers such as zinc oxide, limestone, silica, mica, barytes, lithophone, zinc sulphide, talc, calcium carbonate, clays, powdered metals and alloys such as bismuth, brass, bronze, cobalt, copper, iron, nickel, tungsten, aluminum, tin, etc. Limestone is ground calcium/magnesium carbonate and is used because it is an inexpensive, heavy filler. Preferably, the specific gravity of the plug is at least 2.0. More preferably, the plug has a specific gravity of at least 2.2.
Examples of various suitable heavy filler materials which can be included in the present invention are as follows:
When the end of the hollow channel at the outer edge of the core has a shoulder, the plug is formed so that it fits into the end of the hollow channel at the shoulder. The plug can be formed so that its outer edge is flush with the outer surface of the core, as shown in
The shape of the plug can vary. Generally, the plug has a shape similar to the shoulder. When the shoulder has generally cylindrical ends, as shown in
Solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis content polybutadiene and a metal salt of an α, B-ethylenically unsaturated carboxylic acid such as zinc mono-or diacrylate or methacrylate. To achieve higher coefficients of restitution in the core, the manufacturer may include fillers such as small amounts of a metal oxide such as zinc oxide. In addition, lesser amounts of metal oxide can be included in order to lighten the core weight so that the finished ball more closely approaches the USGA® upper weight limit of 1.620 ounces.
Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiators such as peroxides are admixed with the core composition so that on the application of heat and pressure, a complex curing cross-linking reaction takes place.
In a preferred embodiment, the core composition comprises at least one highly neutralized ionomer containing high levels of fatty acids or metal salts of fatty acids. The highly neutralized ionomer containing high levels of fatty acids or metal salts of fatty acids are very durable materials, especially when molded into a neat sphere to form a core. Generally, the highly neutralized ionomers containing high levels of fatty acids or metal salts of fatty acids have a higher C.O.R. than a similar core formed of traditional materials such as polybutadiene. The C.O.R. of the core is generally at least 0.800, preferably greater than 0.810, and more preferably greater than 0.820. The specific gravity is generally less than 1.0. The highly neutralized ionomers containing high levels of fatty acids or metal salts of fatty acids may be used filled or unfilled, but it is preferable if it is unfilled as it has better properties such as durability and C.O.R. Using a highly neutralized ionomer containing high levels of fatty acids or metal salts of fatty acids would also allow the use of heavier weights or magnets, thereby increasing the initial moment of inertia of the golf ball.
Examples of commercially available highly neutralized ionomers containing high levels of fatty acids or metal salts of fatty acids include HPF materials available from DuPont. Additionally, the materials may be produced using methods known in the art, and other materials, such as the materials described for use as cover materials may be used for golf ball cores, such as those described in U.S. Pat. Nos. 5,306,760; 5,312,857; 5,542,677; 5,591,803; 6,100,336; 6,350,815; 6,469,102; and 6,743,847, all of which are hereby incorporated by reference, may be utilized in whole or in part.
It will be understood that a wide array of other core configurations and materials could be utilized in conjunction with the present invention. For example, cores disclosed in U.S. Pat. Nos. 5,645,597; 5,480,155; 5,387,637; 5,150,9136; 5,588,924; 5,507,493; 5,503,397; 5,482,286; 5,018,740; 4,852,884; 4,844,471; 4,838,556; 4,726,590; and 4,650,193; all of which are hereby incorporated by reference, may be utilized in whole or in part.
The core comprises a single or multiple layers.
A core and mantle or interior layer may be used to further define a hollow channel. Core and mantle layers suitable for the present invention are disclosed in U.S. Pat. Nos. 6,193,618; 6,309,312; and 6,244,977, as well as those previously described. The hollow channel extends inwardly from the outer edge of the mantle layer, through the mantle layer, and into the core. The end of the hollow channel may have its end near the center of the core, or alternatively, extend through the core and have its second end at the outer edge of the mantle layer.
A core comprising a metal spherical center and a layer disposed about the center can define a hollow channel.
The cover used in the present golf ball may utilize any cover composition and/or configuration known in the art. The cover may be a single or multi-layer cover. Single cover layer golf ball compositions for use in the present invention include those disclosed in U.S. Pat. Nos. 6,126,559; 6,120,393; 5,971,872; 5,833,553; 5,820,489; 5,803,831; 5,733,207; 5,645,497; 5,580,057; 5,507,493; 5,470,075; and 5,368,304, entirely incorporated herein by reference.
Multi-layer covers and compositions for use in the present golf ball include those disclosed in U.S. Pat. Nos. 6,224,498; 6,220,972; 6,213,894; 6,210,293; 6,204,331; 6,152,834; 6,149,536; 6,083,119; 6,042,488; 5,971,871; 5,873,796; and 5,830,087, entirely incorporated herein by reference.
The preferred method of making the present golf ball includes the following steps. First, at least one hollow channel is radially formed in the golf ball core. The channel may be formed by drilling from the outer edge of the golf ball core into the core near the center at a predetermined length. A shoulder can be formed at the end of the hollow channel near the outer edge of the core by a countersink drilling operation. Alternatively, two halves of a core may be formed having recesses wherein the two halves are combined in order to form a golf ball core having one or more channels and optional shoulder. Or, the channels may be “molded in” using retractable non-stick coated (i.e., Teflon® coated) pins during core molding. Once the channels are formed, at least one movable weight is inserted into each channel. An optional spring or spring-like device is inserted into the hollow channel and is attached to be in continuous contact with the weight. A plug is then inserted to cover the end of the hollow channel.
The spring may be inserted before the movable weight so the weight is between the spring and plug or inserted into the hollow channel after the insertion of the movable weight, so that the spring is positioned between the weight and plug. The spring or spring-like device may be connected to the core, weight, or plug. It is noted that if the weights and plugs comprise a magnet, the spring or spring-like device is not required.
Alternatively, multi-layered cores, mantle cores and finished golf balls may also be drilled for inserting movable weights and springs. The finished balls may then be plugged by using materials which normally form the outer layer of a golf ball. The plugs may be ultrasonically-bonded or spin-bonded.
The following examples illustrate various aspects of the present invention. The examples are provided for the purposes of illustration and are in no way intended to limit the scope of the invention.
Cores having a diameter of 1.545 inches were formed having the following formulation (amounts of ingredients are in parts per hundred rubber (phr) based on 100 parts butadiene rubber):
The cores were subsequently drilled at five equally-spaced locations on the equator using a 0.25 inch width drill bit to form five radially extending hollow channels. The five equally spaced hollow channels extended inwardly to near the center of the core but the center of the core was maintained. The mass of the core was measured as follows.
A steel spherical ball for use as the moveable weight was inserted into each hollow channel. Each weight had a diameter of 0.219 inches and the total weight of the steel balls was 3.497 grams.
A compression spring having a length of 1 inch, a load of 0.38 lbs., a deflection of 0.82 inches at load, and a rate of 0.48 lbs./in. was cut into two 0.50 inch springs. A 0.50 inch spring was inserted into each hollow channel. The total weight of the five springs equaled 0.28 grams.
The five holes of the hollow channels on the surface of the core were enclosed with a plug formed from crosslinked core stock. The plug was inserted into the end of the hollow channel and was secured with epoxy resin. After curing, the surface was sanded and smoothed.
The core was placed on a battery-powered spin tester and oriented such that the plane within which the five hollow channels, springs, and movable weights are disposed generally extended vertically. The axis of rotation of the spin tester was vertical. The core was then spun. At near maximal spin rate, the core changed its orientation so that the plane having the five hollow channels, springs, and moving weights was perpendicular to the spin axis. The change in orientation of the golf ball core occurred at a spin rate of about 2500 rpm. The springs maximally compressed at 4800 rpm. The maximal speed of the spin tester is 7941 rpm.
For comparison, a control core was used having five hollow channels in the core but no weights or springs disposed within those channels. The core was inserted into the spin tester so that the plane having the five hollow channels was substantially vertical. The comparison core, when spun, maintained its vertical orientation and did not shift to a horizontal orientation at any spin rate.
Cores were molded having the following formulation (amounts of ingredients are in parts per hundred rubber (phr) based on 100 parts butadiene rubber):
The slugs formed from the above formula, which were used to form cores, had a slug weight of 38.5 to 39.0 grams. The cores were semi-translucent and had the following properties:
Hollow channels were drilled into the cores with a 0.25 inch diameter counterbore tip drill. The hollow channels had a length of 0.600 inches and a 0.375 inch diameter countersink region at the end of the outer edge of the core forming a shoulder. The weight loss of the hollow channels and countersink equaled 3.47 grams per core.
The ends of the hollow channels on the surface of the core were then enclosed with plugs having the formulation disclosed in Table 4. The plug composition was cured before the ends of the hollow channels were enclosed by the plugs.
The plug composition exhibited a specific gravity of 2.223.
Two identical cores were assembled having five hollow channels and a shoulder at the end of the hollow channel along the outer edge of the core. Both cores were assembled with plugs having the above formulation, 0.50 inch springs, and 0.219 inch diameter steel balls. The first plug was molded into the plaques mold wherein the plug was molded at about 0.110 inches thick. The second core used the same stock but was reinforced with an aluminum window screen mesh molded on both sides of the plug stock in the plaque mold. The plug including the mesh had a thickness of about 0.130 inches. The disks were cut to size with a 0.375 inch plug cutter. Table 5 below compares the two cores.
Core #2 having the aluminum mesh plug was tested for its coefficient of restitution. Table 6 below shows the results:
After four firings, the core was spun in a spin tester and continued to find the correct axis. The core was cut in half and sanded. The springs and steel balls were still functional.
Core slugs were formed having the following formulation:
The slug weight of the above composition was 38–39 grams. Cores were formed from the slugs with the following properties:
The cores were centerless ground. The size of the core was 1.503 inches and the weight was 31.78 grams.
Six cores were drilled with a counterbore so that each core had five hollow channels and shoulders at the end of the hollow channel at the outer edge of the core. The weight loss due to the drilling of the hollow channels was 3.39 grams so that the core after drilling five hollow channels weighed 28.39 grams.
Another six cores were drilled with a counterbore so that each core had three hollow channels and shoulders at the end of the hollow channel at the outer edge of the core. The weight of the core after three hollow channels and shoulders were drilled was 29.65 grams. Different moving weights and springs were inserted into the three hollow channels and five hollow channel cores as shown in Table 9 below.
Covers having similar formulations to the covers used in TOP-FLITE® XL golf balls were injected-molded onto each core.
Each steel ball used above had a diameter of 0.219 inches and a mass of 0.699 grams. The brass balls used above had a diameter of 0.219 inches and a mass of 0.772 grams. The springs exhibited the same properties as the springs used in Example 1.
The plugs enclosing the ends of the hollow channel at the outer surface of the core employed the same plug formulation as in Example 2. Each plug had a diameter of 0.365 inches, a thickness of 0.125 inches and a mass of 0.489 grams.
Golf ball Type A above was fired at 125 feet per second (C.O.R. speed). The C.O.R. was 0.793. Calculated typical values of a golf ball having a variable M.O.I. are shown below in Table 10.
Golf ball Type C above was fired 21 times and did not break. The average C.O.R. was 0.786 with the minimum C.O.R. measuring at 0.763 and the maximum C.O.R. measuring at 0.799. The standard deviation was 0.011. The difference in C.O.R. was due to hitting the ball on the pole (i.e., no holes) versus on the equator (with holes, springs, balls, and plugs).
Two types of test balls were made using the method previously described. One type had three channels, each containing one 0.250 inch diameter lead shot weighing 1.56 grams and one compression spring having a load rating of 0.38 pounds deflection. The second type had two channels, each containing one 0.230 inch diameter tungsten metal ball weighing 1.92 grams and one compression spring having a load rating of 0.38 pounds deflection. These balls were finished and tested on a mechanical golfing machine (Iron Byron) using a Top-Flite® Intimidator Driver at 132 feet per second club head speed. The machine was set up to produce a high pull slice on the control golf ball. All balls were placed on the tee randomly with regard to pole and equator orientation. Both of the test balls reduced slices from 43 to 47% compared to the conventional solid two piece control ball.
A ball according to
As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.
This application is a continuation-in-part of U.S. application Ser. No. 10/015,527, filed Dec. 13, 2001 now U.S. Pat. No. 6,755,753.
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| Number | Date | Country | |
|---|---|---|---|
| 20050003906 A1 | Jan 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10015527 | Dec 2001 | US |
| Child | 10875487 | US |
