U.S. patent application number 09/766165 was filed with the patent office on 2001-10-25 for avoidance of resonance in the inflatable sport ball by limiting the critical ratio.
Invention is credited to Axe, John D., Brown, Ken, Lacroix, Matthew K., LaLiberty, Ronald P., Veilleux, Thomas A..
Application Number | 20010034279 09/766165 |
Document ID | / |
Family ID | 25075601 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010034279 |
Kind Code |
A1 |
Veilleux, Thomas A. ; et
al. |
October 25, 2001 |
Avoidance of resonance in the inflatable sport ball by limiting the
critical ratio
Abstract
A sport ball having an internal device such as an internal pump
has a critical ratio that insures that rebound characteristics or
coefficient of restitution of the ball, such as a basketball, will
be acceptable for use. The invention also includes the method for
evaluating design and/or quality control of a sport ball by
measuring the internal vibration and determining the critical ratio
of the sport ball.
Inventors: |
Veilleux, Thomas A.;
(Charlton, MA) ; Lacroix, Matthew K.;
(Belchertown, MA) ; LaLiberty, Ronald P.; (Dudley,
MA) ; Brown, Ken; (Tolland, CT) ; Axe, John
D.; (Lecanto, FL) |
Correspondence
Address: |
MICHELLE BUGBEE, ASSOCIATE PATENT COUNSEL
SPALDING SPORTS WORLDWIDE INC
425 MEADOW STREET
PO BOX 901
CHICOPEE
MA
01021-0901
US
|
Family ID: |
25075601 |
Appl. No.: |
09/766165 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09766165 |
Jan 19, 2001 |
|
|
|
09594980 |
Jun 15, 2000 |
|
|
|
09594980 |
Jun 15, 2000 |
|
|
|
09478225 |
Jan 6, 2000 |
|
|
|
60159311 |
Oct 14, 1999 |
|
|
|
60252443 |
Nov 21, 2000 |
|
|
|
Current U.S.
Class: |
473/593 |
Current CPC
Class: |
F04B 33/00 20130101;
A63B 41/12 20130101; F16K 15/202 20130101; A63B 41/00 20130101;
A63B 2041/005 20130101; F16K 15/147 20130101 |
Class at
Publication: |
473/593 |
International
Class: |
A63B 041/12 |
Claims
What is claimed:
1. A sport ball comprising a self-contained inflation mechanism,
wherein said sport ball comprising a self-contained inflation
mechanism has substantially the same rebound characteristics as a
corresponding sport ball that does not comprise a self-contained
inflation mechanism.
2. The sport ball of claim 1, wherein the sport ball is hollow.
3. The sport ball of claim 1, wherein the sport ball is a
basketball.
4. The sport ball of claim 3, wherein the basketball is a
regulation size basketball.
5. The sport ball of claim 3, wherein the basketball is a
non-regulation size basketball.
6. The sport ball of claim 1, wherein the basketball is a youth
size basketball.
7. The sport ball of claim 1, wherein the sport ball is a soccer
ball.
8. The sport ball of claim 1, wherein the sport ball comprises a
cover wherein the material is selected from the group consisting of
leather, synthetic leather, composites, rubber materials and
combinations thereof.
9. The sport ball of claim 1, wherein the sport ball is a football,
volley ball or playground ball.
10. A sport ball according to claim 3, wherein the rebound
characteristics of the ball comprise the rebound distance of the
ball when dropped vertically from a height of 72 inches, and the
ball has a rebound of 50-57 inches.
11. A sport ball according to claim 10, wherein the difference
between the maximum and minimum rebound heights of the ball is 5.5
inches or less.
12. A sport ball according to claim 11, wherein the ball has a
coefficient of restitution of 0.750-0.813.
13. A sport ball according to claim 12, wherein the delta COR of
the ball is 0.051 or less.
14. A sport ball according to claim 12, wherein the delta COR of
the ball is 0.036 or less.
15. A sport ball according to claim 3, wherein the difference
between the maximum COR and minimum COR of the ball when the ball
is dropped repeatedly with different orientations is 0.051 or
less.
16. A sport ball according to claim 3, wherein the difference
between the maximum COR and minimum COR of the ball when the ball
is dropped repeatedly with different orientations is 0.036 or
less.
17. A sport ball according to claim 4, wherein the difference
between the maximum COR and minimum COR of the ball when the ball
is dropped repeatedly with different orientations is 0.051 or
less.
18. A sport ball according to claim 1, wherein the rebound
characteristics of the ball comprise the rebound consistency of the
ball.
19. A sport ball according to claim 1, wherein the rebound
characteristics of the ball include the minimum critical ratio of
the ball, wherein the minimum critical ratio is equal to (half
period of component vibration)/(duration of the ball's impact with
the floor).
20. The sport ball of claim 1, wherein the self-contained inflation
mechanism is a pump.
21. A sport ball having a self contained inflation mechanism and
exhibiting a minimum critical ratio equal to: (half period of
component vibration)/(duration of the ball's impact with the
floor), wherein the critical ratio is selected such that the sport
ball having the self contained inflation mechanism exhibits
substantially the same minimum critical ratio as a comparable sport
ball without a self contained inflation mechanism.
22. The sport ball of claim 21, wherein the sport ball is a
basketball.
23. The sport ball of claim 21, wherein the sport ball is a soccer
ball.
24. The sport ball of claim 21, wherein the sport ball comprises a
cover wherein the material is selected from the group consisting of
leather, synthetic leather, composites, rubber materials and
combinations thereof.
25. The sport ball of claim 21, wherein the sport ball is a
football, volley ball or playground ball.
26. The sport ball of claim 21, wherein the self contained
inflation mechanism is a pump.
27. A method of determining the critical ratio of an inflated sport
ball, comprising the steps of: a) determining the duration of the
ball's impact with the floor; b) determining the half period of
component vibration; calculating the critical ratio by dividing the
half period of component vibration, (b), by the duration of the
ball's impact with the floor, (a).
28. A method according to claim 27, wherein the steps (a) and (b)
are performed repeatedly with different ball orientations.
29. The method of claim 27, wherein the sport ball is a
basketball.
30. The method of claim 27, wherein the critical ratio is 0.95 or
greater, and the basketball is suitable for play.
31. The method of claim 27, wherein the sport ball is a football,
volley ball, soccer ball or playground ball.
32. A sport ball which comprises a self-contained inflation
mechanism, the sport ball having rebound characteristics determined
by dropping the ball repetitively with different orientations from
a height of 72 inches onto a wooden floor and measuring the rebound
height that occurs when respective surface areas of the ball
contact the floor, wherein the ball has rebound characteristics
according to which the maximum rebound height minus the minimum
rebound height is less than or equal to 5.5 inches.
Description
RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part of and claims the
benefit of U.S. patent application Serial No. 09/594,980, filed
Jun. 15, 2000. That application is a Continuation-in-Part of and
claims the benefit of U.S. patent application Ser. No. 09/478,225,
filed Jan. 6, 2000, and further claims the benefit of U.S.
Provisional Application No. 60/159,311, filed Oct. 14, 1999.
[0002] The applicant also claims priority based on a provisional
U.S. patent application Ser. No. 60/252,443, filed Nov. 21, 2000
entitled "Avoidance of Resonance in the Inflatable Sport Ball by
Limiting the Critical Ratio."
FIELD OF THE INVENTION
[0003] The present invention relates to sport or game balls,
preferably inflatable sport balls, and more preferably, inflatable
sport balls with a mechanism for inflating or adding pressure to
the ball, or other internal device, inside the ball.
BACKGROUND OF THE INVENTION
[0004] The present invention relates to all inflatable sport balls
including those that contain pump mechanisms for inflating or
adding pressure to the balls, or which contain another internal
device within the ball. The mechanism for inflating or adding
pressure to the ball is preferably a pump. Examples of other
internal devices, referred to herein as components, which may be
self-contained in the sport balls include, but are not limited to,
a storage container, a flashlight, a key holder, a watch, and the
like. In some cases, such balls have an inherent asymmetric
construction. Even if a counterweight is positioned at a directly
opposite portion of the ball from the pump mechanism or other
component, the ball assembly still is asymmetric when considered
from other axes.
[0005] Conventional inflatable sport balls, such as basketball,
footballs, soccer balls, volleyballs and playground balls, are
inflated through a traditional inflation valve using a separate
inflation needle that is inserted into a self-sealing inflation
valve. A separate pump, such as a traditional bicycle pump, is
connected to the inflation needle and the ball is inflated using
the pump. The inflation needle is then withdrawn from the inflation
valve that self-seals to maintain the pressure. This system works
fine until the sport ball needs inflation or a pressure increase
and a needle and/or pump are not readily available.
[0006] Internal vibration in a sport ball may adversely affect the
performance of the sport ball. For example, a basketball with
vibration problems may not dribble or bounce consistently, and a
soccer ball may roll or travel inconsistently or away from the
intended target when kicked or thrown. If the sport ball is a sport
ball with a self contained inflation mechanism, such as a pump, or
other internal device, there is an increased potential for
vibration problems due to the added internal component. One of the
worst internal vibration problems is a condition called resonance.
Resonance, as used herein, is when the impact loading of an object,
such as a ball, occurs in tune with the object's natural frequency
of vibration. The natural frequency of the ball is the frequency
that the ball oscillates at in the absence of external forces.
There is a need for a method to measure this vibration and minimize
it in the final product so that the consumer does not notice the
vibration. Examples of sport balls which may be affected include,
but are not limited to, any inflatable sport ball such as a
basketball, volleyball, soccer ball, football, playground ball or
other inflated ball.
SUMMARY OF THE INVENTION
[0007] An object of the invention is to provide a sport ball having
an internal pump, wherein the ball exhibits the same degree of
bounce consistency when dropped repeatedly with various
orientations as a corresponding sport ball that does not include an
internal pump.
[0008] Another object of the invention is to provide a method of
measuring the bounce consistency of a sport ball.
[0009] The present invention is directed to a sport ball having an
internal device, whereby the sport ball having the internal device
conforms to the same specifications as a corresponding sport ball
that does not contain an internal device. The invention achieves
the above-noted objectives and provides a method for measuring the
internal vibration and determining the critical ratio of a sport
ball, thereby enabling the design of a sport ball with internal
device, wherein the ball is suitable for use in competitive
play.
[0010] One preferred form of the invention is a sport ball
comprising a self-contained inflation mechanism, wherein said sport
ball comprising a self-contained inflation mechanism has
substantially the same rebound characteristics as a corresponding
sport ball that does not comprise a self-contained inflation
mechanism. The self-contained inflation mechanism preferably is a
pump.
[0011] The sport ball preferably is hollow, but also can contain a
foam or other material. The ball can be a regulation or youth size
basketball, soccer ball, football, volley ball or playground ball.
The ball preferably comprises a cover formed from a material
selected from the group consisting of leather, synthetic leather,
composites, rubber materials, and combinations thereof.
[0012] Methods of characterizing the rebound characteristics of the
ball include, but are not limited to, coefficient of restitution
(COR), rebound height, rebound consistency, and critical ratio. A
basketball comprising a self-contained inflation mechanism
according to the invention preferably has a coefficient of
restitution range of 0.750-0.813 when tested repeatedly at
different ball orientations, combined with a difference between the
maximum and minimum coefficient of restitution values of 0.051 or
less. In another preferred form of the invention, the difference
between the maximum and minimum coefficient of restitution values
is 0.036 or less. When described by rebound height, a basketball of
the invention has a rebound height of 50-57 inches when dropped on
a wooden floor from a height of 72 inches. The difference between
the maximum and minimum rebound heights when the ball is dropped
repeatedly with different orientations is 5.5 inches or less and
more preferably 4 inches or less. In another preferred form of the
invention, the basketball has a rebound height of 50-54 inches when
dropped on a wooden floor from a height of 72 inches.
[0013] In a preferred form of the invention, the sport ball having
a self-contained inflation mechanism has a minimum critical ratio
which is substantially the same as the critical ratio of a
corresponding sport ball that does not comprise a self-contained
inflation mechanism. The critical ratio is defined as the half
period of component vibration divided by the duration of the ball's
impact with the floor. Preferably, the critical ratio is 0.95 or
greater.
[0014] Another form of the invention is a method of determining the
critical ratio of an inflated sport ball, comprising the steps
of:
[0015] a) determining the duration of the ball's impact with the
floor,
[0016] b) determining the half period of component vibration, and
calculating the critical ratio by dividing the half period of
component vibration, (b), by the duration of the ball's impact with
the floor (a).
BRIEF DESCRIPTION OF THE DRAWING
[0017] The invention will be better understood by reference to the
accompanying drawings in which:
[0018] FIG. 1 shows a cross section of a portion of a sport ball
with a self-contained piston and cylinder arrangement operable from
outside the ball for adding air pressure to the ball.
[0019] FIG. 2 is a side view of the pump shown in FIG. 1.
[0020] FIG. 3 is an isometric view of the cap for the pump of FIG.
1 showing the configuration for locking and unlocking the pump
piston.
[0021] FIG. 4 is a detailed cross-section view of a one-way valve
assembly for use on the exit of the pump of FIG. 1.
[0022] FIG. 5 is a more detailed view of the duckbill valve in the
FIG. 4 assembly.
[0023] FIG. 6 is a diagrammatic view showing the critical ratio
versus maximum minus minimum rebound height for various basketball
designs.
[0024] FIG. 7 is a graph of COR versus rebound height for a
basketball according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] In a preferred embodiment, the sport ball is an inflated
sport ball with a self contained inflation mechanism or other
internal device. The interior of the sport ball may also be hollow
or may contain a foamed material. The sport ball may be any sport
ball, such as, but not limited to, a basketball, a football, a
soccer ball, a volleyball, or a playground ball, and it is
preferably a basketball with a self contained inflation mechanism
or other internal device, more preferably a basketball with a self
contained inflation mechanism such as a pump.
[0026] The invention will be better understood by first considering
the structure of a typical ball incorporating one embodiment of an
inflation pump. Referring first to FIG. 1 of the drawings, a
portion of a sport ball 10 is illustrated incorporating one
embodiment of an inflation pump. The ball 10 which is illustrated
is a typical basketball construction comprising a carcass 15 having
a rubber bladder 12 for air retention, a layer 14 composed of
layers of nylon or polyester yarn windings wrapped around the
bladder 12 and an outer rubber layer 16. For a laminated ball, an
additional outer layer 18 of leather or a synthetic material
comprises panels that are applied by adhesive and set by cold
molding, or other process known in the art for adhering panels to
the ball. The windings are preferably randomly oriented and two or
three layers thick. The windings form a layer which cannot be
expanded to any significant degree and which restricts the ball
from expanding to any significant extent above its regulation size
when inflated above its normal playing pressure. This layer for
footballs, volleyballs and soccer balls is referred to as a lining
layer and is usually composed of cotton or polyester cloth that is
impregnated with a flexible binder resin such as vinyl or latex
rubber.
[0027] Incorporated into the carcass of the ball of the invention
during the formation is the rubber pump boot or housing 20 with a
central opening and with a flange 22 which is bonded to the bladder
using a rubber adhesive. The boot is located between the rubber
bladder 12 and the layer of windings 14. An aluminum molded plug is
inserted into the boot opening during the molding and winding
process to maintain the proper shape central opening and to allow
the bladder to be inflated during the manufacturing process. The
central opening through the boot 20 in configured with a groove 24
to hold the flange 26 on the upper end of the pump cylinder 28. The
cylinder can optionally be bonded to the boot using any suitable
flexible adhesive (epoxy, urethane or other.) The pump boot or
housing has a groove 25 which contributes to the bounce consistency
of the ball.
[0028] Located in the pump cylinder 28 is the pump piston 30 which
is shown in FIGS. 1 and 2. The piston includes an annular groove 32
at the bottom end, which contains the spring 34 which forces the
piston up in the cylinder 28. Also, at the bottom end of the piston
30 is a circumferential O-ring groove 36 containing an O-ring 38.
As seen in FIG. 1, this O-ring groove 36 is dimensioned such that
the O-ring 38 can move up and down in the groove 36. The O-ring is
forced into the position shown in FIG. 1 when the piston is pushed
down. In this position, the O-ring seals between the cylinder wall
and the upper flange 40 of the groove 36. When the piston 30 is
forced up by the spring 34, the O-ring 38 moves to the bottom of
the groove 36 which opens up a by-pass around the O-ring through
the recesses 42 so that the air can enter the cylinder 28 below the
piston 30. Then, when the piston is pushed down, the O-ring moves
back up to the top of the groove and seals to force the air out
through the cylinder exit nozzle 46.
[0029] At the upper end of the piston are the two flanges 48 which
cooperate with a cylinder cap 50 to hold the piston down in the
cylinder and to release the piston for pumping. The cylinder cap 50
is fixed into the top of the cylinder 28 and the piston 30 extends
through the center of the cylinder cap 50. The cap 50 is cemented
into the cylinder 28. FIG. 3 shows an isometric view of the bottom
of the cylinder cap 50 and illustrates the open areas 52 on
opposite sides of the central opening through which the two flanges
48 on the piston can pass in the unlocked position. In the locked
position, the piston is pushed down and rotated such that the two
flanges 48 pass under the projections 54 and are rotated into the
locking recesses 56. Attached to the upper end of the piston 30 is
a button or cap 58 that is designed to essentially completely fill
the hole in the carcass and to be flush with the surface of the
ball. This button may be of any desired material such as cast
urethane or rubber. Mounted on the upper surface of the cylinder
cap 50 is pad 60 which is engaged by the button 58 when the piston
is pushed down against the spring force to lock or unlock the
piston. The pad provides cushioning to the pump and should also be
flexible to match the feel of the rest of the ball. Its surface
should be textured to increase grip.
[0030] FIG. 1 of the drawings shows a pump exit nozzle 46 but does
not show the one-way valve that is attached to this exit. Shown in
FIG. 4 is a one-way valve assembly 62 of the duckbill-type to be
mounted in the exit nozzle 46. This assembly comprises an inlet end
piece 64, an outlet end piece 66 and an elastomeric duckbill valve
68 captured between the two end pieces. The end pieces 64 and 66
are preferably plastic, such as a polycarbonate, and may be
ultrasonically welded together.
[0031] Although any desired one-way valve can be used on the exit
nozzle 46 and although duckbill valves are a common type of one-way
valves, a specific duckbill configuration is shown in FIG. 4 and in
greater detail in FIG. 5. The duckbill structure 68 is formed of an
elastomeric silicone material and is molded with a cylindrical
barrel 70 having a flange 72. Inside of the barrel 70 is the
duckbill 74 which has an upper inlet end 76 molded around the
inside circumference into the barrel 70. The walls or sides 78 of
the duckbill 74 then taper down to form the straight-line lower end
with the duckbill slit 80. The duckbill functions in the
conventional manner where inlet air pressure forces the duckbill
slit open to admit air while the air pressure inside of the ball
squeezes the duckbill slit closed to prevent the leakage of air.
Such a duckbill structure is commercially available from Vemay
laboratories, Inc. of Yellow Springs, Ohio.
[0032] A pump assembly of the type described and illustrated in
FIGS. 1-5 is preferably made primarily from plastics such as
polycarbonate or high impact polystyrene, most preferably from
polycarbonate. Although the assembly is small and light weight,
perhaps only about 25 grams, it is desirable that a weight be added
to the ball structure to counterbalance the weight of the pump
mechanism.
[0033] Other forms of the invention may utilize different pump
constructions and the precise sequence of manufacturing steps may
vary in various forms of the invention. Those skilled in the art
will recognize the substantial benefits including the economies of
construction inherent in allowing the pumping mechanism to be
designed to accommodate the environmental considerations inherent
in normal use of the sports ball and not the much harsher
conditions that are encountered during the manufacturing
process.
[0034] In the context of basketball performance testing, rebound
height is defined as the height the top of a basketball attains
when dropped from 72 inches onto a wooden floor surface. (Although
the description of the preferred embodiment is phrased in terms of
a basketball, it will be understood that the invention has
application to other sports balls, such as soccer balls,
volleyballs, footballs and playground balls.) The rebound height
can also be described in terms of a coefficient of restitution
(COR). The mathematical relationship between rebound height and
coefficient of restitution is described below in example 1. In a
rebound test, the surface upon which the ball is dropped is
designed to simulate a regulation basketball-playing surface, and
it is a two inch thick wooden piece securely attached to a
foundation. The rebound height can vary for a particular ball when
it is dropped on different spots on the ball. A useful measure of
rebound height variability is the difference between the maximum
rebound height and the minimum rebound height. It is a desirable
feature to have basketball rebound height as uniform as possible
when the ball is dropped repetitively with different orientations.
Player testing shows that basketballs with maximum minus minimum
rebound height of five and one half inches or more are difficult to
play with and control and are difficult to dribble. The basketballs
with maximum minus minimum rebound height of five inches or less
are acceptable for play and show no obvious dribbling problem.
Basketballs with maximum minus minimum rebound height of four
inches or less are preferred. Additionally, it has been found that
a basketball generally must rebound to a height of between fifty
and fifty-six inches overall to be acceptable, although individual
preferred rebound height may vary from player to player.
[0035] The act of bouncing a basketball, or other sport ball, on a
floor is a dynamic event with impact loading, elastic deformation
and vibration. In a perfect impact, the kinetic energy of motion is
entirely converted into elastic deformation of a ball. The elastic
deformation is like loading a spring or diving board; it deforms,
then it springs back. After motion stops (i.e., when the ball is at
its maximum deformation), the energy stored in the deformation is
released and all of the energy is converted into rebound velocity.
The rebound velocity provides the ball enough energy to rise to the
original drop height under perfect impact conditions.
[0036] In reality, impact is not perfect. When components of the
basketball vibrate after impact, they rob some of kinetic energy of
the impact. This acts to store some of the energy in the form of
local vibrations that cannot be recovered and are not converted
into rebound velocity. The end result is to reduce the rebound
height. Typically, the location on the basketball with the minimum
rebound height coincides with the maximum vibration of the
component. In contrast, the location on the basketball with maximum
rebound height corresponds to a minimum amount of component
vibration. It is therefore required to map the surface of the
basketball such that rebound height is known for all points on the
ball. Typical mapping of the entire surface of the ball will
require rebound testing on each panel of the ball at approximately
five points per panel. The panel that where the pump is located
will have additional points tested, generally at one-half to one
inch increments along the panel. Additionally, the two ends of the
ball are also tested. Each point is tested several times to find
the maximum and minimum. The difference between maximum and minimum
rebound height can then be determined.
[0037] A "quick test" may be utilized once a full mapping scheme
for a particular product has been determined. This quick test
utilizes the data previously acquired when mapping the entire
surface of the sport ball, and then tests only those locations
where the maximum and minimum points are expected. Although the
quick test is not as accurate, it may be utilized for quick
decisions regarding the vibration and rebound of a sport ball.
[0038] Two critical factors must be considered in the study of the
impact of a ball on a floor. The first factor is the nature of the
impact loading, and the second factor is the natural frequency of
the ball. The natural frequency of the ball is affected by the
vibration of the internal device or component (i.e., a self
contained inflation mechanism or other internal device) in the ball
or part of the ball. The natural frequency of the ball with an
internal component is measured with the internal device or
component installed in the ball. As used herein, the term natural
frequency of the ball is the lowest vibration frequency of the ball
with the internal device installed in the ball. The impact loading
is the force acting on the ball to decelerate it to a stop on the
floor, backboard, rim, etc. and cause the ball to bounce back. The
quantities of interest are the force and time history. The natural
frequency of the ball influences how fast and to what extent the
ball will respond to the impact and how much of the impact energy
will be stored in local ball vibrations. The period of vibration is
the time required to complete one cycle of motion. The period of
vibration is equal to one divided by the frequency of
vibration.
[0039] This invention includes a novel method to quickly analyze a
sport ball. This invention has particular application to a
basketball, although the invention is not limited to such balls.
The inventors have now found that the ratio of two critical impact
parameters are directly related to the maximum minus minimum
rebound height. The two critical impact parameters are the duration
of the ball's impact with the floor and the half period of
component vibration. The half period vibration for a basketball
having a self-contained inflation device installed is equal to one
half of the inverse of the natural frequency of the installed
component. The critical ratio is most easily measured when the
ball, with the component installed, is dropped on the spot that
yields the minimum rebound height. As previously described herein,
the minimum rebound height is found by mapping the surface of the
ball. The "quick test" may be used once a surface is mapped for the
same construction sport ball, but small changes to the component or
the materials will require complete mapping to determine the proper
locations that yield maximum and minimum rebound heights. As used
herein, "critical ratio" refers to the half period of component
vibration divided by the duration of the ball's impact with the
floor. (Although this description is most relevant to a basketball
and a pump, it will be understood that the invention has
application to other sport balls and other components, preferably
other sport balls with a pump.)
[0040] The duration of the ball's impact with the floor can be
measured with high speed digital imaging. It will be understood
that the duration refers to the duration of contact of the ball
with the floor, and the duration of impact does not vary with drop
location. The duration of impact should be measured at the location
yielding the minimum rebound height. The ball's impact with the
floor is first captured with the high speed digital imaging system.
A frame sampling rate of about 9,000 to 13,500 frames per second is
preferably recommended. Analysis of the set of images will indicate
the number of image frames that the ball is in contact with the
floor. The duration of the impact event is simply the total number
of frames that the ball is in contact with the floor divided by the
frame sampling rate.
[0041] The half period of vibration of a basketball or other sport
ball can also be measured using high speed digital imaging.
Analysis of the set of images allows the determination of the
number of frames between the maximum and the minimum length of
vibration for a basketball having a self-contained inflation
device. The half period of vibration for a basketball having a
self-contained inflation device is simply the total number of
frames between maximum and minimum vibration divided by the frame
sampling rate. If the minimum vibration is difficult to estimate,
an alternate method may be used to determine the half period of
component vibration. Using the alternate method, the number of
frames between one maximum and the next maximum limit of vibration
is determined. In this method, the half period of component
vibration is the total number of frames between the two maximums
divided by two, and then divided by the frame sampling rate.
Alternatively, the half period of basketball vibration can also be
determined by measuring the natural frequency directly with an
accelerometer. As indicated above, the half period of vibration is
equal to one half of the inverse of the frequency. Alternatively,
dropping the ball onto a load cell and measuring the force over
time may be used to measure the duration of the ball's impact.
[0042] FIG. 6 illustrates test data for a plurality of basketballs.
For each basketball, the maximum minus the minimum rebound height
was determined by mapping the surface of the basketball.
Thereafter, the critical ratio for each of these basketballs was
determined by testing. Each point or dot in the diagrammatic view
of FIG. 6 represents the test results for a single basketball.
These test results corroborate decisively a strong negative
correlation. More particularly, FIG. 6 establishes that the maximum
minus minimum height increases as the critical ratio decreases.
[0043] In other words, the parameter that best correlates to
maximum minus minimum rebound height for any specific basketball is
the half period of vibration for a basketball having a
self-contained inflation device divided by the duration of the
ball's impact with the floor. The quotient of these numbers is
referred to herein as the critical ratio. When this critical ratio
is less than 0.95 for a regulation basketball, the maximum minus
minimum rebound height is generally greater than five and one half
inches, and the ball is therefore likely to be unacceptable for
play due to dribbling problems. When this critical ratio is greater
than or equal to 0.95, the maximum minus minimum rebound height is
generally less than or equal to five inches, and the ball is
therefore suitable for play. This critical ratio can be used in the
design and development phase, as well as during quality control, to
determine if an inflated ball will have rebound problems. If
necessary, design changes may be made to minimize the vibration
before producing balls to be sold to customers.
[0044] Examples of the factors that affect the critical ratio
include, but are not limited to, the stiffness modulus, flex
modulus, bulk modulus, tension modulus and compression modulus
values of each of the components of the ball, including the panels,
carcass, bladder, windings, and boot; the inertia and mass of the
pump or other internal component, the local stiffness of the
component's support, the air pressure in the ball, and the quality
of the bond between the component's housing (the "boot") and the
bladder and cover.
EXAMPLE 1
[0045] A regulation size synthetic leather basketball was made
having a diameter of 9.43 inches (23.95 cm), a circumference of
29.5 inches (75 cm), a weight of about 600 grams. The ball
contained an integral pump of the type shown in FIGS. 1-5. The pump
was configured to increase the pressure of the ball by at least 1
psi for every 200 pump strokes. The rebound of the ball when it was
dropped from a height of 72" (measured from the bottom of the ball)
onto a wooden surface designed to simulate the floor of a
basketball court was determined when the ball was dropped
repeatedly with different orientations. The ball was found to have
a rebound height in the range of 50-57 inches on all panels of the
ball (measured from the top of the ball), with a difference between
the maximum and minimum rebound heights of 5.5 inches or less. The
lowest rebound height resulted when the portion of the ball surface
that was located about 2 inches away from the pump was the part
that contacted the wooden surface.
EXAMPLE 2
[0046] The procedure of Example 1 was repeated with a different
basketball of the same type, and the basketball was found to have a
rebound height in the range of 50-54 inches on all panels of the
ball (measured from the top of the ball), with a difference between
the maximum and minimum rebound heights of 4 inches or less.
EXAMPLE 3
[0047] The coefficient of restitution (COR) corresponding to
various rebound heights for the balls described in Examples 1 and 2
was determined according to the following formula:
COR=V.sub.H/V.sub.I
[0048] wherein
[0049] V.sub.I is the downward velocity of the ball upon initial
impact with the floor, and
[0050] V.sub.H is the velocity of the ball as it travels upward
immediately after impact with the floor.
[0051] Velocity for an object traveling vertically can be defined
by the equation
v.sup.2=2ax
[0052] Where v is velocity, a is acceleration due to gravity, x is
the distance to the floor from the initial drop point. 1 More
specifically , V 1 = 2 ( 32.2 ft . / s 2 ) ( 12 in / ft ) ( x in )
And V H = 2 ( 32.2 ft / s 2 ) ( 12 in / ft ) ( h - d in ) Stated
another way , V H / V I = h - d x
[0053] Wherein, h is the rebound height, and d is the ball
diameter.
[0054] Furthermore, delta COR was determined by subtracting the COR
corresponding to the minimum rebound height of a particular ball
from the COR corresponding to the maximum rebound height of the
same ball. The calculated velocity, COR and delta COR results are
shown below on Table 1. The data of Table 1 is plotted on FIG. 7,
also shown below. Thus, a ball with a rebound of 50 inches has a
COR of 0.7506, and a ball with a rebound of 54 inches has a COR of
0.7868. The ball of Example 1 was found to have a delta COR of
0.051. The ball of Example 2 was found to have a delta COR of
0.036. Thus, for both of these balls, the maximum and minimum COR
values for any single measurement were in the overall range of
0.750-0.813.
1TABLE 1 COR for Basketball Rebound Height Test Height Velocity COR
(in) (in/sec) (n/a) Initial 72 235.88 -- Rebound 40 153.70 0.6516
41 156.20 0.6622 42 158.65 0.6726 43 161.07 0.6828 44 163.45 0.6929
45 165.80 0.7029 46 168.11 0.7127 47 170.39 0.7224 48 172.65 0.7319
49 174.87 0.7413 50 177.07 0.7506 51 179.24 0.7598 52 181.38 0.7689
53 183.50 0.7779 54 185.59 0.7868 55 187.66 0.7956 56 189.71 0.8042
57 191.73 0.8128 58 193.74 0.8213 59 195.72 0.8297 60 197.69 0.8381
Min Max Delta COR (in) (in) (n/a) Rebound 50 55 0.0449 Rebound 51
56 0.0444 Rebound 52 57 0.0439 Rebound 53 58 0.0434
[0055] The invention has been described with reference to the
preferred embodiments. Modifications and alterations will occur to
others upon reading and understanding the preceding detailed
description. It is intended that the invention be construed as
including all such alterations and modifications insofar as they
come within the scope of the claims and the equivalents
thereof.
* * * * *