U.S. patent application number 14/343190 was filed with the patent office on 2014-08-07 for bend-twist coupled golf club shaft.
This patent application is currently assigned to UNIVERSITY OF FLORIDA RESEARCH FOUNDATION, INC.. The applicant listed for this patent is Jarrod Mark Bonsmann, Peter G. Ifju, David A. Jenkins. Invention is credited to Jarrod Mark Bonsmann, Peter G. Ifju, David A. Jenkins.
Application Number | 20140221122 14/343190 |
Document ID | / |
Family ID | 47832773 |
Filed Date | 2014-08-07 |
United States Patent
Application |
20140221122 |
Kind Code |
A1 |
Ifju; Peter G. ; et
al. |
August 7, 2014 |
BEND-TWIST COUPLED GOLF CLUB SHAFT
Abstract
Embodiments of the subject invention relate to a method and
apparatus for providing a golf club shaft that has coupling between
one or more bending modes and one or more twisting modes of
deformation. In a specific embodiment, bending the shaft along a
central longitudinal axis of the shaft in a plane of bending
results in twisting of the shaft about the same central
longitudinal axis of the shaft.
Inventors: |
Ifju; Peter G.; (Newberry,
FL) ; Bonsmann; Jarrod Mark; (Lake Mary, FL) ;
Jenkins; David A.; (Gainesville, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ifju; Peter G.
Bonsmann; Jarrod Mark
Jenkins; David A. |
Newberry
Lake Mary
Gainesville |
FL
FL
FL |
US
US
US |
|
|
Assignee: |
UNIVERSITY OF FLORIDA RESEARCH
FOUNDATION, INC.
GAINESVILLE
FL
|
Family ID: |
47832773 |
Appl. No.: |
14/343190 |
Filed: |
September 6, 2012 |
PCT Filed: |
September 6, 2012 |
PCT NO: |
PCT/US2012/053992 |
371 Date: |
April 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61531172 |
Sep 6, 2011 |
|
|
|
Current U.S.
Class: |
473/319 ;
473/316 |
Current CPC
Class: |
A63B 53/10 20130101;
A63B 53/00 20130101; A63B 60/00 20151001; A63B 2209/02
20130101 |
Class at
Publication: |
473/319 ;
473/316 |
International
Class: |
A63B 53/10 20060101
A63B053/10 |
Claims
1. A golf club, comprising: a head; and a shaft, wherein a first
portion of the shaft comprises coupling between bending the first
portion of the shaft along a first portion of the central
longitudinal axis of the shaft in a first plane of bending and
twisting the first portion of the shaft about the first portion of
the central longitudinal axis of the shaft.
2. The golf club according to claim 1, wherein the first portion of
the shaft is the shaft such that the shaft comprises coupling
between bending the shaft along the central longitudinal axis of
the shaft in a plane of bending and twisting the shaft about the
central longitudinal axis of the shaft.
3. The golf club according to claim 2, wherein the shaft comprises
a proximal end and a distal end, wherein the head is connected to
the distal end.
4. The golf club according to claim 3, wherein the shaft comprises
a shear center with respect to the proximal end being held fixed
and a bending load being applied to the distal end, wherein the
shear center is offset from the central longitudinal axis of the
shaft in a direction perpendicular to the longitudinal axis.
5. The golf club according to claim 2, wherein a cross-sectional
shape of the shaft with respect to the central longitudinal axis of
the shaft is circular.
6. The golf club according to claim 2, wherein the shaft has a
bending stiffness along the central longitudinal axis of the shaft
that is constant for all planes.
7. The golf club according to claim 2, wherein a clockwise
torsional stiffness of the shaft about the central longitudinal
axis of the shaft with respect to a clockwise torque applied at the
distal end and the proximal end is equal to a counter-clockwise
torsional stiffness of the shaft about the central longitudinal
axis of the shaft with respect to a counter-clockwise torque
applied at the distal end and the proximal end.
8. The golf club according to claim 2, wherein a clockwise
torsional stiffness of the shaft about the central longitudinal
axis of the shaft with respect to a clockwise torque applied at the
distal end and the proximal end is equal to a counter-clockwise
torsional stiffness of the shaft about the central longitudinal
axis of the shaft with respect to a counter-clockwise torque
applied at the distal end and the proximal end for all elemental
lengths of the shaft.
9. The golf club according to claim 2, wherein the central
longitudinal axis of the shaft is approximately a straight line
when no bending forces are applied to the shaft.
10. The golf club according to claim 4, wherein a center of mass of
the head is offset from the central longitudinal axis of the shaft
by a center of mass offset, wherein the center of mass offset is
greater than zero.
11. The golf club according to claim 10, wherein an offset-caused
twist tends to occur when the club is rotationally accelerated
about the proximal end in the plane of bending.
12. The golf club according to claim 10, wherein the shear center
is offset from the central longitudinal axis of the shaft by a
distance in the range of 10% to 300% of the center of mass
offset.
13. The golf club according to claim 12, wherein the shear center
is offset from the central longitudinal axis of the shaft in the
same rotational direction with respect to the central longitudinal
axis as the center of mass offset is offset from the central
longitudinal axis of the shaft.
14. The golf club according to claim 12, wherein the shear center
is offset from the central longitudinal axis of the shaft in an
opposite direction as the center of mass offset is offset from the
central longitudinal axis of the shaft.
15. The golf club according to claim 12, wherein the shear center
is offset from the central longitudinal axis of the shaft at a
shear center offset rotational angle with respect to the central
longitudinal axis, wherein the center of mass is offset from the
central longitudinal axis at a center of mass offset rotational
angle with respect to the central longitudinal axis, wherein the
shear center offset rotational angle is between 0.degree. and
180.degree. or between 180.degree. and 360.degree. away from the
center of mass offset rotational angle
16. The golf club according to claim 12, wherein the distance is in
the range of 90% to 110% of the center of mass offset.
17. The golf club according to claim 12, wherein the distance is in
the range of 10% to 100% of the center of mass offset.
18. The golf club according to claim 12, wherein the distance is in
the range of 100% to 300% of the center of mass offset.
19. The golf club according to claim 2, wherein there is
approximately zero coupling between bending the shaft along the
central longitudinal axis of the shaft in a second plane that is
perpendicular to the plane of bending and twisting the shaft about
the central longitudinal axis of the shaft.
20. The golf club according to claim 3, wherein the shaft is
tapered from a first cross-sectional area of the proximal end of
the shaft to a second cross-sectional area at the distal end of the
shaft, wherein the first cross-sectional area is greater than the
second cross-sectional area.
21. The golf club according to claim 4, wherein the shear center is
offset from the central longitudinal axis of the shaft by a
distance in a range of 0.1 inch to 8 inches.
22. The golf club according to claim 2, wherein the shear center is
offset from the central longitudinal axis of the shaft by a
distance in a range of 0.1 radii of the distal end of the shaft and
30 radii of the distal end of the shaft.
23. The golf club according to claim 11, wherein the coupling
between bending the shaft and twisting the shaft causes a coupling
twist in an opposite direction as the offset-caused-twist.
24. The golf club according to claim 11, wherein the coupling
between bending the shaft and twisting the shaft causes a coupling
twist in a same direction as the offset-caused-twist.
25. The golf club according to claim 2, wherein the coupling
between bending the shaft and twisting the shaft extends a portion
of the swing of a user where a face of the head is within 5 degrees
of being square to the plane of bending when the user swings the
club in the plane of bending.
26. The golf club according to claim 2, wherein the coupling
between bending the shaft and twisting the shaft at least partially
compensates for a slice of a user swinging the golf club in the
plane of bending.
27. The golf club according to claim 2, wherein the coupling
between bending the shaft and twisting the shaft at least partially
compensates for a hook of a user swinging the golf club in the
plane of bending.
28. The golf club according to claim 2, wherein a torsional moment
caused by an impact with an object by the head during a user
swinging the golf club in the plane of bending is at least
partially compensated for due to the coupling between bending the
shaft along the central longitudinal axis of the shaft and twisting
the shaft about the central longitudinal axis of the shaft.
29. The golf club according to claim 2, wherein the shaft comprises
a material having an anisotropic stiffness, wherein the material
has a first axis of stiffness and a second axis of stiffness
perpendicular to the first axis of stiffness, wherein a first
stiffness along the first axis of stiffness is greater than a
second stiffness along the second axis of stiffness, wherein the
first axis of stiffness is at an angle with respect to the central
longitudinal axis greater than 0.degree. and less than 90.degree.,
and wherein the material contributes to the bend/twist
coupling.
30. The golf club according to claim 29, wherein the first
stiffness is at least 2 times the second stiffness.
31. The golf club according to claim 29, wherein the first
stiffness is at least 10 times the second stiffness.
32. The golf club according to claim 29, wherein the first
stiffness is at least 100 times the second stiffness.
33. The golf club according to claim 2, wherein there is at least
0.1.degree. of twisting of the shaft for every 2% of a length of
the shaft deflection of a distal end of the shaft with respect to a
position of the central longitudinal axis before bending of the
shaft.
34. The golf club according to claim 29, wherein the material
comprises carbon fibers.
35. The golf club according to claim 29, wherein the material is
positioned such that a first orientation of the first axis of the
material of a first half of the shaft is a mirror image of a second
orientation of the first axis of the material of a second half of
the shaft, wherein the first half and second half are separated by
a separation plane perpendicular to the plane of bending, wherein
the central longitudinal axis is in the separation plane, wherein a
first orientation of the second axis of the material in the first
half of the shaft is a mirror image of a second orientation of the
second axis of the material in the second half of the shaft.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit of U.S.
Provisional Patent Application Ser. No. 61/531,172, filed Sep. 6,
2011, the disclosure of which is hereby incorporated by reference
in its entirety, including any figures, tables, or drawings.
BACKGROUND OF INVENTION
[0002] In a normal golf swing, the shaft of the golf club bends a
substantial amount. Generally, the shaft bends in the early part of
the forward swing, because of the weight (mass) of the head tends
to lag when the club is accelerated. In the later part of the
forward swing, after the ball has been impacted, the club bends the
opposite direction since the club head inertia continues through
while the swing is decelerated.
[0003] Additionally, the shaft of a typical club twists during the
forward swing because the club head is not centered with the axis
of the shaft, or stated in another manner the center of mass of the
club head is offset from the plane of swing of the golfer, and a
torsion is developed in the shaft during the forward swing. This
twist can have a negative effect on achieving a square club face at
the moment of impact of the club head with the golf ball. If the
head is twisted out at impact, for example twisted clockwise when
viewed from the shaft handle to the club head for a right handed
golfer's swing, the ball can tend to be hit to the right of
straight ahead, or slice. Alternatively, if the club is twisted in
at impact, such as twisted counter-clockwise when viewed from the
handle to the club head for a right handed golfer's swing, the
force applied to the golf ball again will not be straight ahead and
can tend to hit the ball to the left of straight ahead, such that
the ball can hook. Of course, there are other reasons that slices
and hooks occur, but, in general, in order to hit the ball in the
intended direction (straight ahead), the club face should
preferably be square during the impact of the club face with the
ball. By square at impact, it is meant that the face of the club
head is in a plane perpendicular to the plane of the swing when the
face of the club head contacts the golf ball.
[0004] Traditional shafts offer a narrow window, or portion of the
golf swing, where the club face is square or substantially square,
where substantially square can mean the club face is within a
certain angle, such as one degree or two degrees, of being square.
That window is sandwiched between portions of the swing where the
club shaft is untwisting from the twist caused by the initial
acceleration of the forward swing, and a portion of the swing where
the club shaft then twists after impacting the ball, due to
deceleration of the swing. Accordingly, there is a need for a golf
club shaft that increases the portion of a golf swing where the
club face is square or substantially square. Further, there is a
need for a golf club that allows a golfer to alter the shape of the
ball trajectory, such as adding to or reducing a fade or a
draw.
BRIEF SUMMARY
[0005] Embodiments of the subject invention relate to a method and
apparatus for providing an elongated club shaft that has coupling
between one or more bending modes and one or more twisting modes of
deformation, or bend/twist coupling. Specific embodiments can
incorporate bend/twist coupling such that bending along the
longitudinal axis of the shaft in a first plane incorporating the
longitudinal axis results in twisting of the shaft about the
longitudinal axis and bending in a second plane incorporating the
longitudinal axis, wherein the second plane is perpendicular to the
first plane, does not result in any twisting of the shaft about the
longitudinal axis. In this way, bending the shaft about the
longitudinal axis of the shaft in a third plane incorporating the
longitudinal axis that is at an angle with respect to the first
plane between 0 and 90 degrees results in twisting about the
longitudinal axis, but less twisting than bending in the first
plane.
[0006] Specific embodiments pertain to hollow elongated shafts with
bend/twist coupling; elongated shafts with a circular outer
circumference cross-sectional shape, having bend/twist coupling;
elongated shafts with a taper along the length of the shaft, having
bend/twist coupling; and a hollow elongated shaft with a circular
outer circumference cross-sectional shape, with a taper along the
length of the shaft, having bend/twist coupling, where one or more
of these embodiments can be golf club shafts. In specific
embodiments, the elongated shafts can have length to diameter
ratios of at least 10:1, at least 20:1, at least 30:1, at least
40:1, at least 50:1, at least 100:1, at least 150:1, and/or at
least 200:1. In embodiments having a tapered shaft, these ratios
can be based on the diameter of the small diameter end of the shaft
(such as end of a golf club shaft that connects to the golf club
head), can be based on the diameter of the large diameter end of
the shaft (such as the handle end of a golf club shaft), can be
based on the diameter at the midpoint of the elongated shaft
(midpoint of length), can be based on the average diameter along
the length of the shaft, or can be based on some sort of effective
diameter of the shaft.
[0007] Normal golf club shafts do not have this bend/twist
coupling, such that bending does not significantly affect twist and
twist does not significantly affect bending. For elongated shafts
having bend/twist coupling, bending the shaft along certain axes
leads to a predictable twisting deformation. In a specific
embodiment, bending the shaft along a central longitudinal axis of
the shaft results in twisting of the shaft about the same central
longitudinal axis of the shaft. Incorporating bend/twist coupling
into a golf club shaft can lead to more accurate ball contact,
and/or control, on a more frequent and repeatable basis.
Embodiments of the subject invention pertain to golf clubs that can
correct for undesirable tendencies such as slices and/or hooks.
Further embodiments can orient the shaft (rotation) with respect to
the club head (e.g., face of club head) such that the orientation
can add to or reduce a fade or draw, or otherwise affect the ball
trajectory of the golf shot in a desired manner. Embodiments of the
subject invention relate to all types of golf clubs, including, but
not limited to, putters, wedges, irons, fairway woods, drivers, and
hybrids.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 shows an overhead view of a golf swing, showing the
bend of the shaft as well as the accumulated twist of the shaft
shown by the twist angle.
[0009] FIG. 2A shows how a golf club shaft in accordance with an
embodiment of the subject invention keeps the club face more square
through the impact zone than a traditional shaft.
[0010] FIG. 2B shows a superposition of several club head locations
near the point of contact with the golf ball for a club head on a
traditional shaft and a club head on a shaft in accordance with the
subject invention.
[0011] FIG. 3 shows the impact offset of the ball impact location,
which produces a torsional moment about the shaft axis when the
ball is impacted.
[0012] FIG. 4 shows the deflection vs. twist of a golf club shaft
in accordance with an embodiment of the subject invention, loaded
in cantilever loading.
[0013] FIG. 5 shows a perspective view of an embodiment of a shaft
in accordance with the subject invention.
[0014] FIG. 6 shows a cross-section of the shaft shown in FIG.
5.
[0015] FIG. 7 shows a shaft before and after bending.
[0016] FIGS. 8A and 8B show the shaft of FIG. 5 relative to a swing
plane, at two different angles of rotation about the longitudinal
axis.
[0017] FIGS. 9A-9H show an embodiment of a club head showing
various angles of rotation the shaft of FIG. 5 can have with
respect to the club head.
[0018] FIG. 10 shows a c-channel being pushed down at one end at
two differences places of applied force.
[0019] FIG. 11 shows a plank shaped piece of material before and
after having a distal end of the material pushed down.
[0020] FIGS. 12A-12D show cross-sections of various embodiments of
shafts in accordance with the subject invention.
DETAILED DISCLOSURE
[0021] Embodiments of the subject invention relate to a method and
apparatus for providing a golf club shaft that has coupling between
one or more bending modes and one or more twisting modes of
deformation. Normal shafts do not have this bend/twist coupling,
such that bending does not significantly affect twist and twist
does not significantly affect bending. For bend/twist coupling,
bending the shaft along certain axes leads to a predictable
twisting deformation about the axes. In a specific embodiment,
bending the shaft along a central longitudinal axis of the shaft in
a plane of bending results in twisting of the shaft about the same
central longitudinal axis of the shaft. Such bend/twist coupling
effect can have at least two primary benefits, which are described
below. Bending along an axis at a certain rotational angle with
respect to the shaft can be used to describe the bending.
Alternatively, the bending can be described as bending in a plane.
These two descriptions are equivalent when the axis along which the
bending occurs is in the plane, and the plane makes the same angle
with respect to the shaft as the certain rotational angle makes
with respect to the shaft. Referring to FIG. 5, bending could be
described as bending along longitudinal axis 24 at an angle made by
line segment AB with respect to the longitudinal axis 24, or
described as bending in the plane incorporating the longitudinal
axis and line segment AB.
[0022] Embodiments of the present invention relate to a golf club
having a shaft that bends the same in all directions along a
central longitudinal axis of the shaft, twists the same about the
central longitudinal axis in the clockwise direction as in the
counter-clockwise direction, is circular in cross-sectional shape,
and utilizes bend/twist coupling to provide improvements in
performance and to help golfers deal with common swing flows. By
bending the same in all directions it is meant that the shaft has
the same bending stiffness for all planes of bending with respect
to bending along the central longitudinal axis of the shaft. By
twists the same about the central longitudinal axis it is meant
that the torsional stiffness in a clockwise direction about the
central longitudinal axis is the same as the torsional stiffness in
a counter-clockwise direction about the central longitudinal axis.
The circular cross-sectional shape can vary in diameter (taper)
along the central longitudinal axis.
[0023] Twist of the golf club shaft is generally considered to be
deleterious. Twist can occur due to, for example, the offset of the
center of mass of the club-head with respect to the longitudinal
axis of the shaft, where the offset of the center of mass is a
distance from the longitudinal axis of the shaft to the center of
mass of the club head in a direction normal to a plane, such as the
plane of the swing of a golfer swinging the club. During down-swing
acceleration of the club, the center of mass of the head being
offset from the shaft causes twisting of the shaft. This phenomenon
is depicted in FIG. 1. FIG. 1 shows an overhead view of a golf
swing for a right handed golfer, showing the bend of the shaft, as
well as the accumulated twist of the shaft, shown as the twist
angle. For illustration, the relative rotational position of the
shaft and club head has been simplified, and exaggerated, in order
to illustrate the effect described. Actual swings of golfers can
vary as to the rotational position the golfer holds the shaft in at
various points in the swing, the curved path the shaft takes during
the golfer's swing, and the position on the shaft (e.g., handle)
that the golfer applied forces and/or torque to the shaft at
various points of the swing, as well as other aspects of the
golfer's swing that may affect the bending and/or twisting of the
shaft. As shown in FIG. 1, the shaft twists clockwise, when viewed
from the handle to the club head, during the initial portion of the
forward swing. During a specific swing, the shaft untwists to a
square position at the moment of impact with the ball. In other
swings, the ball may be struck before, or after, the square
position and, thus, lead to applying a force to the ball that is
not straight ahead, potentially resulting in an errant shot.
Although FIG. 1 shows contact with the ball occurring when the arc
of the swing is nearest the ground, other swings can result in
contact with the ball occurring earlier or later, depending on the
preference of the golfer for a particular shot.
[0024] Traditional shafts offer a very narrow window where the club
face is square. That window is sandwiched between where the club
untwists from the initial acceleration during the initial portion
of the forward swing that causes the shaft to twist, and where the
shaft then twists after the impact zone due to deceleration during
the latter portion of the forward swing. This phenomenon is
depicted in FIGS. 1 and 2B, where FIG. 1 shows an overview of a
golf swing with a traditional shaft, and FIG. 2B shows a
superposition of the location and twist of the club head through
the window just before contact between the club face and the ball
and just after contact between the club face and the ball. Although
FIG. 1 shows the ball being contacted at the point of the swing
where the club head is closest to the ground, the ball can be
contacted earlier or later in the swing, as desired by the golfer.
By incorporating bend/twist coupling, a shaft can be designed to
tend to twist in the opposite direction from the twist that would
tend to be caused by the inertia of the club head when bent along
certain axes. In a specific embodiment, a golf club shaft can
incorporate bend/twist coupling such that the shaft tends to twist
inward in the early part of the forward swing and then tends to
twist outward in the latter part of the forward swing.
Incorporating such bend/twist coupling can effectively cancel the
twist due to the mass of the club head being offset from the
longitudinal axis of the shaft in a direction normal to a plane,
such as the plane of the swing. Hence a window, or portion of the
forward swing, where the club face of the club head is square, or
within plus or minus an angle .phi. of being square, can be
substantially extended. In this way, this window can cover a longer
portion, or all of, the impact zone, where the impact zone is the
portion of the forward swing during which the club head contacts
the golf ball. Extending this window makes the club much more
forgiving and, thus, can improve shot consistency. In specific
embodiments, .phi. is 1.degree., 2.degree., 3.degree., 4.degree.,
5.degree., 6.degree., 7.degree., 8.degree., 9.degree., or
10.degree.. Therefore, by incorporating such bend/twist coupling,
the criticalness of swing timing can be reduced and the likelihood
of a good shot can be enhanced.
[0025] In addition to making the club more forgiving to imperfect
swing timing, shafts can be fabricated to compensate for poor
swings, such as consistent slicing or hooking. By adjusting the
amount of bend/twist coupling, a specific deficiency, such as a
slice can be partially, or completely, compensated for. The head of
the club can also be positioned relative to the shaft to compensate
for poor swings.
[0026] Another benefit that can result from incorporating
bend/twist coupling comes at the instant when the ball is impacted
by the club head. When the club head impacts the ball, the impact
force on the club head is typically offset from the longitudinal
axis of the shaft in a direction normal to the plane of the swing
when the club is square by a distance which can be referred to as
the impact offset, as shown in FIG. 3. The force times the impact
offset distance equals the torsional moment applied to the shaft by
the impact force. This torsional moment causes the shaft to tend to
twist upon impact. By incorporating bend/twist coupling in the
shaft, the torsional moment applied to the shaft by the impact
force can be partially, or completely, compensated for.
[0027] The shear center of a shaft incorporating bend/twist
coupling is related to the mechanics of the materials of the shaft.
The shear center can be defined as distance from the longitudinal
axis of the shaft, in a direction normal to a plane, such as the
plane of the swing, that application of an impact force parallel to
the plane of the swing, or the moment caused by the club head
offset, results in little or no twisting of the club shaft about
the longitudinal axis. The shear center is defined assuming the
proximal end of the shaft (handle end) is held fixed and the impact
force, or other force, is applied at the distal end (club head end)
at a certain distance from the point of the proximal end held
fixed. The shear center may change if the force is applied at a
different distance from the point of the proximal end held fixed.
For specific embodiments, any force applied through the shear
center results in no twisting, independent of the direction of the
force, such that bending is achieved without twisting. The shear
center can be positioned inside or outside of the shaft, and in the
case of the shear center being positioned outside of the shaft, the
force through the shear center is applied via a structure (such as
a club head) rigidly affixed to the distal end of the shaft such
that the shear center lies on the structure.
[0028] Referring to a shaft with a shear center, and the impact
force direction through the shear center, the impact force of the
ball on the club head at a distance from the longitudinal axis in a
direction normal to the plane of the swing tends to twist (first
type twist) the shaft about the longitudinal axis, but also tends
to bend the shaft along the longitudinal axis, which tends to twist
(second type twist) the shaft about the longitudinal axis in an
opposite direction to the first twist. When the impact is at the
shear center, or in a direction passing through the shear center,
no first type twist occurs due to the impact, because the first
type twist cancels the second type twist. If the shear center of
the shaft coincides with the center of mass offset of the club
head, then the twist (third type twist) that tends to be caused by
the mass of the club head during acceleration of the golf club
during the initial portion of the forward swing and deceleration of
the golf club during the later portion of the forward swing will be
offset by the second-type twist. In this case, the third type of
twist tending to be caused can cause bending of the shaft.
Accordingly, if the shear center coincides with the center of mass
offset of the club head, and the golf ball is contacted by the club
face at a distance from the longitudinal axis in a direction normal
to the plane of the swing that equals the shear center, little, or
no, twist will occur. Further, when the shear center of the shaft
is at the same distance from the longitudinal axis as the impact
location, the shaft will appear torsionally rigid, yet retain
bending compliance.
[0029] The shear center of the shaft at the distal end can be
oriented with respect to the shaft such that it is in the opposite
direction of the center of mass offset of the club head. Twist of
the second type (twist caused by bend twist coupling) would be in
the opposite direction as that if the shear center was oriented in
the same direction as the club head offset. This second type of
twist would add to instead of cancel the twist of the first type
(that caused by the offset mass). Additional embodiments through
all orientations of the shaft with respect to the club head would
lead to various degrees from acting to cancel through increasing
the degree of first type twist.
[0030] The shaft and club head can be designed such that, with a
certain orientation of the shaft (i.e., shear center) with respect
to the club head, a fade can be enhanced, or reduced, with respect
to hitting the ball the same way with a golf club without
bend-twist coupling, or a draw can be enhanced, or reduced, with
respect to hitting the ball the same way with a golf club without
bend-twist coupling.
[0031] Embodiments of the subject invention relate to shafts that
have a shear center that changes position with respect to the
distance along the shaft from the proximal end of the shaft. The
shear center can vary in a variety of measures. Specific
embodiments involve a shear center that remains at a certain
rotational angle with respect to the longitudinal axis of the
shaft, where the shear center can then continuously move away from
the longitudinal axis (e.g., monotonically increasing, linearly
increasing, exponentially increasing, or other function with
respect to distance along the shaft from the proximal end of the
shaft) as the distance along the shaft away from the proximal end
increases. In specific embodiments, the shear center can move
towards or away from, or remain steady, with respect to the
longitudinal axis as the distance along the shaft away from the
proximal end increases, and can go back to the longitudinal axis at
one or more locations along the longitudinal axis, such as when the
shaft reaches the distal end (e.g., where head is attached).
Preferably, the shear center is away from the longitudinal axis at
the distal end such that the shaft as a whole has bend/twist
coupling. In other embodiments, bend/twist coupling can be
implemented at different rotational angles for different portions
of the length of the shaft, be implemented at different amounts for
different portions of the length, can be implemented for only
certain portions of the length, or can be implemented in a variety
of other manners. By implementing bend/twist coupling at different
rotational angles for different portions of the length of the shaft
it is meant that the plane of bending that provides the maximum
bend/twist coupling, where such plane of bend can be said to be at
a certain rotational direction with respect to the longitudinal
axis, can be different for different portions of the shaft. In a
specific embodiment, the rotational direction of the plane of
bending with the maximum bend/twist coupling can vary continuously
along the length of the shaft. Accordingly, the shear center can
rotate as a function of the distance along the shaft from the
proximal end of the shaft, again in a variety of manners, as
desired, such as rotating in a constant direction (clockwise or
counter-clockwise) about the longitudinal axis, rotating back and
forth about the longitudinal axis, remaining at a constant
rotational angle for portions of the length, and rotating about the
longitudinal axis for other portions of the length of the shaft, as
a function of distance along the shaft from the proximal end of the
shaft.
[0032] In specific embodiments, the center of mass offset is within
90% to 110% of the shear center, greater than the shear center,
and/or less than the shear center.
[0033] In further specific embodiments, the desired point of
contact on the face of the club head is within 90% to 110% of the
shear center, greater than the shear center, and/or less than the
shear center. In specific embodiments, the shear center is on the
same side of the longitudinal axis from the shaft as the center of
mass of the club head, and in other specific embodiments, the shear
center is on the opposite side of the longitudinal axis of the
shaft as the center of mass of the club head (such that the
longitudinal axis lies between the shear center and the center of
mass of the club head). By orienting the shaft with the shear
center on the same side of the shaft as the center of mass offset,
the twist due to the center of mass being off the longitudinal axis
can be partially, or fully, compensated for (negated), or a twist
in an opposite direction can be created.
[0034] In further specific embodiments, the shear center is 10% to
300% of the center of mass offset, 10% to 100% of the center of
mass offset, 100% to 300% of the center of mass offset, and/or 90%
to 110% of the center of mass offset. Embodiments of the subject
golf club shafts can have a shear center that is a distance from
the longitudinal axis that is in the range of 0 inches to 12
inches, 0 inches to 5 inches, 1 radius (of the distal end of the
shaft) to 30 radii, less than 1 radius, 1 radius to 5 radii, and
greater than 1 radius.
[0035] In a specific embodiment, both an extension of the window,
or portion of the forward swing, where the club face of the club
head is square, or within plus or minus a desired angle .theta. of
being square can be accomplished, and the torsional moment caused
by the impact force occurring at an impact offset from the axis of
the shaft, can be at least partially compensated for, with the same
shaft design. In other words, by orienting the bend/twist coupled
shaft appropriately with the head of the club, the benefit of
having a more square club face and resistance to twisting during
impact can both be achieved.
[0036] The amount of bend/twist coupling in the shaft can be
controlled by controlling the materials used to manufacture the
shaft and/or the structure of the shaft. In a specific embodiment,
materials having anisotropic behavior can be used for the
manufacture of the shaft in order to achieve bend/twist coupling.
In a further specific embodiment, materials having anisotropic
stiffness can be used for the manufacture of the shaft in order to
achieve bend/twist coupling. In an embodiment, proper alignment of
composite reinforcement, such as carbon fiber or other reinforced
materials, can result in bend/twist coupling of the shaft. In an
embodiment, a proper fiber layup can be used for manufacture of the
club shaft. For example, carbon fibers having an orientation at an
angle to the longitudinal axis between 0.degree. degrees and
90.degree. can contribute to bend/twist coupling and, if not offset
by other materials contributing bend/twist coupling, can contribute
to a new bend/twist coupling of the shaft. The bend/twist coupling
can be mathematically analyzed and/or modeled in order to optimize
the shaft design for a particular application. Shafts in accordance
with embodiments of the subject invention can have length to
diameter (proximal or distal end) ratios in the range of at least
10:1, at least 20:1, at least 30:1, at least 40:1, at least 50:1,
at least 100:1, at least 150:1, at least 200:1, less than 10:1,
less than 20:1, less than 30:1, less than 40:1, less than 50:1,
less than 100:1, less than 150:1, and/or less than 200:1.
[0037] Important properties of the shaft include bending stiffness,
torsional stiffness, and location of the shear center. In addition,
with respect to golf clubs, these same three properties are
important, as well as the orientation of the shaft, rotationally,
with respect to the club head. The bending stiffness of the shaft
is determined by the sectional property of EI, where E is the
effective modulus of elasticity of the material (in units of
Newtons per square meter, N/m.sup.2, or Pascals, Pa) and I is the
moment of inertia of the cross-sectional shape (in units of meters
to the fourth power, m.sup.4), thus yielding units of Newtons times
meters squared or Nm.sup.2. Shafts in accordance with specific
embodiments of the subject invention can have a bending stiffness
in the range from 0.2 Nm.sup.2 to 500 Nm.sup.2. The torsional
stiffness is determined by the sectional property of GJ, where G is
the effective shear modulus of the material (in units of Newtons
per square meter, N/m.sup.2, or Pascals, Pa) and J is the polar
moment of inertia of the cross-sectional shape (in units of meters
to the fourth power, m.sup.4), thus yielding units of Newtons times
meters squared or Nm.sup.2. Shafts in accordance with specific
embodiments of the subject invention can have a torsional stiffness
in the range from 0.1 Nm.sup.2 to 300 Nm.sup.2.
[0038] Referring to FIGS. 5 and 6, an embodiment is shown that was
fabricated using unidirectional carbon fiber prepreg. The carbon
fibers are orientated such that a first axis of stiffness is at an
angle, .theta., to the longitudinal axis of the shaft, where
.theta. is between 0.degree. and 90.degree.. When .theta. is
between 90.degree. and 180.degree., the twist tends to go in the
opposite direction for the same bend. In specific embodiments,
.theta. can remain constant, such as the embodiment shown in FIG. 5
where .theta. is constant for each half 22, 23 of the shaft.
Alternatively, .theta. can vary with radius and/or position along
the length of the shaft, such as the alignment of the carbon fibers
such that the first axis of stiffness follows ellipses that travel
around the contour of the curve of the shaft continuously from half
22 to half 23. This first axis of stiffness is shown in FIG. 5 as
reference number 11 and follows the curve of the tapered
cylindrical shaft. The second axis of stiffness, which is not
shown, is perpendicular to the first axis and also follows the
curve of the tapered cylindrical shaft.
[0039] The first axis of stiffness can follow various patterns,
such as helices, ellipses, or others that provide bend/twist
coupling. The embodiment shown in FIGS. 5 and 6 has two halves of
the shaft 22 and 23, separated by a dividing plane outlined by
reference 12 and 15 such that the two halves 22 and 23 are mirror
images of each other with respect to the plane 12, 15. In this way,
when the shaft is bent, or loaded in cantilever loading, along the
longitudinal axis 24 about line AB (in the swing plane), as shown
in FIG. 7, where the plane defined by 12 and 15 is perpendicular to
the page of FIG. 7, a torsional moment about the longitudinal axis
24 causes the shaft to twist about the longitudinal axis 24.
Reference 21 shows the deflection referred to in FIG. 4, which is
the deflection of the end of the shaft during cantilever loading
while the handle is held in place. In contrast, if the shaft were
bent along the longitudinal axis 24, as shown in FIG. 7, where the
plane defined by 12 and 15 is in the page of FIG. 7, no net
torsional moment, and, therefore, no twisting would occur.
[0040] A variety of materials and shaft structures can be utilized
to achieve the bend/twist coupling in accordance with embodiments
of the subject invention. Fiber reinforced materials such as carbon
fiber reinforced materials can be used. Shafts can be hollow,
and/or have hollow portions, and the entire shaft and/or portions
of the shaft can contribute to the bend/twist coupling.
[0041] FIG. 6 shows a cross-sectional view of the shaft which has a
hollow center, one or more layers of carbon fiber prepreg 18 with
the first axis of stiffness parallel to the longitudinal axis 24,
and one or more layers of carbon fiber prepreg 16 and 17
(corresponding to halves 23 and 22, respectively) with the first
axis of stiffness of the carbon fiber prepreg at an angle .theta.
with respect to the longitudinal axis and in the curve of the
layers 16 and 17. In a specific embodiment, .theta. is less than
45.degree., greater than 0.degree. and less than 90.degree., and/or
greater than or equal to 45.degree. and less than 90.degree..
Preferably, the shaft has the same bending stiffness along the
longitudinal axis at each orientation of the plane 12, 15 with the
page of FIG. 7. Preferably, the torsional stiffness of the shaft is
the same clockwise as it is counterclockwise. Preferably, the
stiffness along a first axis of stiffness for the material having
an anisotropic stiffness used to manufacture the shaft is at least
one and a half orders of magnitude higher, or more preferably at
least two orders of magnitude higher, than the stiffness along the
second axis of stiffness, where the second axis of stiffness is
perpendicular to the first axis of stiffness. Specific embodiments
have stiffness along a first axis that is at least 2 times, at
least 5 times, at least 10 times, at least 50 times, at least 100
times, at least 200 times, at least 500 times, at least 1,000
times, and/or greater than 1000 times the stiffness along the
second (perpendicular) axis.
[0042] Tests show, referring to FIG. 4, that this non-optimized
embodiment can achieve approximately 2 degrees of twist for every 1
inch of deflection, such as the deflection 21 shown in FIG. 7,
under cantilever bending conditions, for a shaft having a length of
approximately 42 inches long and having a taper from the handle end
(larger diameter) to the club head end (smaller diameter). For the
testing, a portion of the proximal end (handle end) was used to
hold the proximal end rigidly fixed in position so the bending of
the shaft could be accomplished and the twisting measured, such
that approximately 39 inches of the 42-inch shaft was bent. This
amount of bend/twist coupling is quite pronounced and well within
the practical range necessary to achieve one or both primary
benefits discussed above. In specific embodiments, the amount of
twist is at least 0.1.degree., at least 1.degree., at least
2.degree., at least 3.degree., and/or at least 4.degree. for every
deflection of 2% of the length of the shaft for a tapered shaft. In
other specific embodiments, the amount of twist is at least
1.degree., at least 2.degree., at least 3.degree., and/or at least
4.degree. for every deflection of 2% of the length of the shaft for
a non-tapered shaft. Additionally, the shear center of the shaft
was measured to be approximately 3 inches from the axis of the
shaft, which allows for the shaft to partially, or completely,
compensate for the torque caused by the impact being at the offset
impact distance away from the longitudinal axis during the ball
strike. A club incorporating a shaft having such benefits can also
allow the shaft to be more flexible, resulting in a higher
club-head speed, while retaining control.
[0043] In a preferred embodiment, the club head is attached to the
shaft such that the plane defined by 12 and 15 is perpendicular to
the plane of the swing such that the bending of the shaft during
the forward swing due to the inertia of the club head is such that,
referring to the bending shown in FIG. 7, the plane defined by 12
and 15 is perpendicular to the page of FIG. 7. FIGS. 8A and 8B show
how the shaft is oriented in this preferred embodiment, such that
the plane defined by 12 and 15 is perpendicular to the swing plane.
In additional embodiments, the shaft can be rotated with respect to
the club head such that the plane defined by 12 and 15 is at an
angle with the plane of the swing between -180.degree. and
180.degree., in order to alter the performance of the golf club. As
an example, the shaft can be rotated with respect to the club head
in order to correct a slice or hook, or for the preference of the
golfer.
[0044] FIGS. 9A-9H show a top view of a golf club head, similar to
the golf club head shown in FIG. 3, with an indication of the
orientation of the plane defined by 12 and 15 within the shaft
shown in FIGS. 5 and 6 indicated by line AB. FIG. 9A shows what can
be referred to as the standard rotational orientation of the shaft
with respect to the club head, where A and B are shown in FIGS. 5,
8A, and 8B. In this standard rotational orientation, when the shaft
bends such that the bottom of the shaft bends to the right looking
down on top of the club head, the shaft rotates such that the club
head tends to rotate counterclockwise looking down on top of the
club head. If the shaft shown in FIG. 9A was in a left-handed club
head, then the shaft can be maintained in the same orientation,
with a left hand club head switched in for the right hand club head
shown, such that A and B are in the same orientation. In this way,
the shaft shown in FIGS. 5, 8A, and 8B can be used in either a
right-handed golf club or a left-handed golf club, in the standard
rotational orientation with respect to the club head. In this way,
for a left hand golfer, when the shaft bends to the left looking
down on top of the club head, the shaft rotates such that the club
head tends to rotate clockwise looking down on top of the club
head.
[0045] There are situations where it can be desirable to rotate the
shaft with respect to the club head away from the standard
position, where FIG. 9A shows the standard position. FIGS. 9B-9H
show various embodiments where the shaft is rotated with respect to
the standard position where FIG. 9B shows an embodiment where the
shaft is rotated counterclockwise between 0.degree. and 90.degree.;
FIG. 9C shows an embodiment where the shaft is rotated
counterclockwise 90.degree.; FIG. 9D shows an embodiment where the
shaft is rotated counterclockwise between 90.degree. and
180.degree.; FIG. 9E shows an embodiment where the shaft has been
rotated either counterclockwise, or clockwise, 180.degree.; FIG. 9F
shows an embodiment where the shaft has been rotated clockwise
between 90.degree. and 180.degree.; FIG. 9G shows an embodiment
where the shaft has been rotated clockwise 90.degree.; and FIG. 9H
shows an embodiment where the shaft has been rotated clockwise
between 0.degree. and 90.degree..
[0046] FIG. 10 shows a piece of c-channel made using an isotropic
material, which is used to show the concept of a shear center, e.
The c-channel is held securely at one end by a bracket 42 or other
apparatus. A force, F.sub.cm, is applied directly over the center
of mass (or centroid) of the c-channel's cross section and as the
end of the c-channel is pushed down to a new position 42, the
c-channel rotates. However, if a bracket 44 is affixed to the
c-channel that allows a force, F.sub.SC, to be applied a distance
away from the position directly over the center of mass (or
centroid) of the cross-section equal to the shear center distance,
e, then, as the c-channel is pushed down, the c-channel does not
rotate. The reason the c-channel does not rotate when the force,
F.sub.SC, is applied at the shear center is that the torsional
moment caused by the force, F.sub.SC, offsets the twisting of the
c-channel.
[0047] FIG. 11 shows a piece of material having a rectangular
cross-section in all directions extending out from a cantilever
support. The piece of material has anisotropic stiffness in at
least the plane of the top of the piece of material, such that the
stiffness along a first axis of stiffness (principal axis shown in
FIG. 11) is higher than the stiffness along a second axis of
stiffness, which is perpendicular to the first axis of stiffness.
In FIG. 11, the first axis of stiffness (principal axis) makes an
angle relative to the longitudinal axis of the piece of material
such that when a force, F.sub.T, is applied to the top of the
distal end of the material, the distal end of the piece of material
tends to rotate about the longitudinal axis. Due to the anisotropic
stiffness of the material, as the force, F.sub.T, is applied, the
distal end rotates around the longitudinal axis, clockwise or
counterclockwise, depending on the angle of the first axis of
stiffness (principal axis) with respect to the longitudinal axis of
the piece of material.
[0048] There are many shaft structure and material combinations
that can provide bend/twist coupling in accordance with embodiments
of the subject invention. In addition to the embodiment shown in
FIGS. 5 and 6, FIG. 12A-12D shows cross sections of a variety of
shaft structures and material combinations that can be utilized in
accordance with the subject invention. FIG. 12A shows an embodiment
that can incorporate a piece of material, such a material as shown
in FIG. 11, with filler material on either side. FIG. 12A shows a
cross-section of the shaft where the middle section is a
cross-section of the piece of material from FIG. 11 cut through the
longitudinal axis. FIG. 12B shows a cross-section of a shaft having
lines representing pieces of material having the properties of the
material shown in FIG. 11 within a background material, such that
each line represents a cross-sectional view of the piece of
material shown in FIG. 11 cut through the longitudinal axis. FIG.
12C shows a cross section through the longitudinal axis of an
embodiment, where the center portions are pieces of material shown
in FIG. 11, much like FIG. 12A. There are hollow portions in FIG.
12C, but these portions can be filled with a filler material. The
outer portions of the embodiment of FIG. 12C can also provide
bend/twist coupling, similar to the embodiment of FIG. 5, or can
use materials without bend/twist coupling. FIG. 12D shows an
embodiment that shows a cross section of a shaft having lines
representing pieces of material having the properties of the
material shown in FIG. 11 within a background material, such that
each line represents a cross-sectional view of the piece of
material shown in FIG. 11 through the longitudinal axis. The
embodiment of FIG. 12D can have an optional one of more hollow
portions within the shaft.
[0049] In a specific embodiment, the materials having anisotropic
properties, such as anisotropic stress/strain properties can be
located along the entire shaft and located uniformly. In further
embodiments, such materials having anisotropic properties, such as
anisotropic stress/strain properties can be located in certain
segments or sections, only on half 23 or half 22, only on portions
of halves 23 and 22, or other combinations of locations to achieve
a desired performance of the golf club.
[0050] All patents, patent applications, provisional applications,
and publications referred to or cited herein are incorporated by
reference in their entirety, including all figures and tables, to
the extent they are not inconsistent with the explicit teachings of
this specification.
[0051] It should be understood that the examples and embodiments
described herein are for illustrative purposes only and that
various modifications or changes in light thereof will be suggested
to persons skilled in the art and are to be included within the
spirit and purview of this application.
* * * * *