CA2049307A1 - Ridged racquet string - Google Patents
Ridged racquet stringInfo
- Publication number
- CA2049307A1 CA2049307A1 CA002049307A CA2049307A CA2049307A1 CA 2049307 A1 CA2049307 A1 CA 2049307A1 CA 002049307 A CA002049307 A CA 002049307A CA 2049307 A CA2049307 A CA 2049307A CA 2049307 A1 CA2049307 A1 CA 2049307A1
- Authority
- CA
- Canada
- Prior art keywords
- string
- ridges
- core
- cross
- millimeters
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- A—HUMAN NECESSITIES
- A63—SPORTS; GAMES; AMUSEMENTS
- A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
- A63B51/00—Stringing tennis, badminton or like rackets; Strings therefor; Maintenance of racket strings
- A63B51/02—Strings; String substitutes; Products applied on strings, e.g. for protection against humidity or wear
-
- A—HUMAN NECESSITIES
- A63—SPORTS; GAMES; AMUSEMENTS
- A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
- A63B51/00—Stringing tennis, badminton or like rackets; Strings therefor; Maintenance of racket strings
- A63B51/02—Strings; String substitutes; Products applied on strings, e.g. for protection against humidity or wear
- A63B51/026—Strings having non-circular cross-section
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B5/00—Making ropes or cables from special materials or of particular form
- D07B5/005—Making ropes or cables from special materials or of particular form characterised by their outer shape or surface properties
- D07B5/006—Making ropes or cables from special materials or of particular form characterised by their outer shape or surface properties by the properties of an outer surface polymeric coating
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B1/00—Constructional features of ropes or cables
- D07B1/16—Ropes or cables with an enveloping sheathing or inlays of rubber or plastics
- D07B1/162—Ropes or cables with an enveloping sheathing or inlays of rubber or plastics characterised by a plastic or rubber enveloping sheathing
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2201/00—Ropes or cables
- D07B2201/20—Rope or cable components
- D07B2201/2083—Jackets or coverings
- D07B2201/2084—Jackets or coverings characterised by their shape
- D07B2201/2086—Jackets or coverings characterised by their shape concerning the external shape
Landscapes
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Physical Education & Sports Medicine (AREA)
- Yarns And Mechanical Finishing Of Yarns Or Ropes (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
A string (10) for a sports racquet, such as a tennis racquet string, is comprised of a string core (20) having a plurality of external ridges (40) bonded thereon for aiding in imparting spin on a ball and for increasing the cross-over contact area between strings. The ridges are parallel to one another and extend axially with the string. Preferably, the string and ridges can be circumscribed by a maximum diameter circle (90), preferably of 1.70 millimeters. The process for making the ridged string includes passing a string core (20) through a bath (72) of resin (71), such as nylon, for coating and glueing the core and then through a die (74) shaped so as to form the ridges (40).
Description
WO 91/1 15~9 PCTtUS90/01698 ~ 33~)7 .
.
,,: ., Ei~l~ Qf the Invention This invention relates in general to a sports racquet string and more specifically involves a string configuration that imparts more spin on the ball and to a method of manufacturing s~ch an improved string.
Background Qf the Inventlon The traditional and most popular cross-section of a sports racquet string is round. Such strings are made typically from natural gut (animal fiber) or from synthetic material,-such as nylon. Conventionally, strings are constructed by twisting many fine filaments of these materials together, with or without a center 20 filament, into a round core strand and then by passing `
the core strand through a round die to apply an outer layer coating.
In general, it is desirable that a string exhibit small damp~ng, that is low energy los~ and high resilience, and good elasticity, that is a low modulus of elasticity. These elements contribute to the playability -of the string. It is also desirable that the string be sufficiently durable.
The diameter of the string is very important as it affects the durability and playability of the string.
Generally, thin strings have superior playability. Thin strings exhibit high resilience and good elasticity, and they maintain longer contact with the ball for greater ;control. ~owever, thin strings may stretch and are more easily broken. On the other hand, thick strings are .
, WO91/11549 PCT/~'S90/0169X
28~ ; 2 stronger and more durable but lack the playability of thin strings.
An additional important characteristic of a string is its ability to impart spin on the ball. For ex,ample, in the game of tennis, a player standing behind the baseline would have to have a height of about six foot seven to see any of the opponent's court without looking thru the net. This means that most hard-hit balls passing over the net and not having forward spin will land out of bounds over the opponent's baseline. Ball spin affects the ball's flight characteristics. When a ball leaves the racquet string bed spinning forward, i.e.
rotating forward on top, it's flight path will tend to curve downward, and it will land earlier and bounce lower. With good top spin, a player can hit a given ball much harder and still have the ball land in. When a ball leaves the racquet string bed spinning backward, i.e.
rotating forward on bottom, its flight path is flatter;
it will tend to land further and bounce higher. Thus, if the player can control spin, the player can control to some degree the trajectory of the ball to advantage.
Again, string characteristics largely determine the amount of spin that can be imparted on the ball. As previously mentioned, the amount of string elongation and resilience determines the amount of time the strings are in contact with the ball. Generally, the thinner the string, the~ greater the contact time. When the ball impacts on the racquet face, the ball remains in contact with the string bed for about three to five thousandths o~f a second. ~During this time, the player is able to impose more control over the direction of ball return and is able to impart spin to the ball to control its flight characteristics.
To put spin on the ball, the ball is struck with the .
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~: :
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:
W091/11549 PCT/~'S90/01698 ~Q49~
', -.
-racket face at an angle to the flight path and the racket face is moved in the plane of the face. Increasing the friction between the strings and the hall has been thought to enhance imparting spin on the ball.
' Synthetic fiber strings, in particular, are excessively smooth in their outer surface and tend to slip over the ball. Many measures have been taken to enhance friction including: roughening t`ne outer surface of the string such as by grinding with abrasives, surface coating the string with frictional or rubbery substances, -twisting or braiding fiber multifiliments, and winding of silk yarns around the string core.
15Synthetic strings treated in the above-described manners tend to have poor dimensional stability and are reduced in strength and elasticity resulting in tension 1088 during play. Further, some are inferior in durability because they exhibit surface aberrations, wearings or breakages due to degredation of the resins, and abrasion, peeling or denaturing of the treating substances. Moreover, since the above-mentioned treatment6 constitute additional 6teps in manufacture, there is an increase in production costs.
Another proposed method to increase string friction is the use of string of polygonal c~oss-section whereby the sharp corners resulting at the juncture of the faces of the polygon are the spin enhancing portions. Two types of polygonal-shaped string have been proposed.
Reta, U.S. Patent No. 4,805,393 proposes the use of a -multi-sided cross-sectional configuration string; Wells, U.S~ Patent No. 4,860,531, proposes a polygonal coating over a round central core.
; Traditional round strings may have a thin, evenly distributed coatin5 around the core to provide protection ::
~ ' . .
:
to the core strands which provide the tensile strength and playability of the string.
As two round strings .cross over one another, due to the very small contact area they weaken one another by indenting one another and by cutting one another in a sawing action as the strings move relative to one another during play. ;
Therefore, it is desirable to have an improved sports racquet string having much better spin-imparting characteristics than a conventional round string and which achieves this without significant loss in playability.
It is further desirable, that such a string reduce the weakening characteristics of string cross-over and therefore be more durable than conventional strings.
-S~M~ARY OF T~ INV~RTION
According to the invention, a string for a sports racquet, such as a tennis racquet string, is comprised of a core having a plurality of ridges thereon for aiding in imparting spin on a ball. The ridges are parallel to one another and extend axially with the string. Preferably, the inner core has a diameter of l.00 - 1.30 millimeters.
ireferably, the ridges are of approximately 0.25 millimeters in height. Preferably, the ridges can be circumscribed by a circle of 1.70 millimeters.
` ~ The process for making the ridged string includes passing a string core through a bath of resin, such as :
nylon, for coating and glueing the core and then through a die shaped so as to form the ridges.
, ~
', WO91/11s4s ~ O~ PCT/US90/01698 Preferably the size, spacing, and number of the ridges increase contact area between strings at the cross-over points and add to the stability to prevent string rotation and movement relative to one another.
Other features and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout.
:: -BRIFF DESCRIPTION OF T~E DRAHING
Figure 1 is a perspective view of a segment of aprefered embodiment of the ridged racquet string of the invention.
Figure 2 i8 a slightly enlarged cross-sectional view of the string of Figure 1 shown passing over a similar string, such as while strung on a racquet.
Figure 3 is a perspective view of a segment of an alternate exemplary embodiment of the ridged racquet string of the invention.
Figure 4 is a slightly enlarged cross-sectional view i~ 30 of the ridged string of Figure 3 shown passing over a ~ similar string, such as while strung on a racquet.
i -~ .
Figure 5 is a view of the extrusion step in the manufacture of the ridged string of the invention.
- ` Figure 6 is a cross-sectional view of an alternate ~ -preferred embodiment of the ridged racquet string of the :`~
WO91/lIS49 PCT/US90/01698 ~ \37 invention; this one having four triangular ridges.
Fig~re 7 is a cross-sectional view of another alternate exemplary embodiment of the ridged racquet string of the invention; this one having three triangular ridges.
DXTAILED D~SCRIPTION OF T~E INVENTION
With reference now to the drawing, and more particularly to Figure 1 thereof, there is shown, in perspective view, a segment of a prefered embodiment of the ridged sports racquet string, denoted generally as 10, of the present invention. Ridged string lC includes a core, denoted generally as 20, and a plurality of ridges 40 bonded to the core 20. Ridges 40 run axially with length of the string and are parallel to one another.
.
Turning now to Figure 2, the ridged string 10 of Figure 1 i8 shown in cross-6ection with the addition of showing the string 10 as it cros6e6 over a similar string 10a such as it would in a strung racquet. The cross-over point of-Figure 2 is simplified in that it does not show the true intermeshing of the strings 10,10a and their ridges 40,40a in the strung condition. At cross-over, the string cores and ridges indent one another and the string cores and ridges protrudé into the concavities between the ridges and core of the cross-over string.
This intermeshing prevents rotation of the strings relative to one another.
~:
In the prefered embodiment shown, the string core 20 is made of construction well-known in the art. Core 20 is of synthetic material and is of composite construction .
::~
wo91/1l5~9 PCT/~'S90/0169X
)7 comprising an inner core 24 and and an outer core 28.
An inner core can be a thick extruded monofilament or be of the "fiber" type. Inner core 24, shown,is of the "fiber" type and comprises a multiplicity of of small diameter monofilament fibers or strands which are twisted and glued together to form the inner core structure. The small monofilament fibers need not be continuous as the friction of the package prevents slippage. In cross-section, a fiber inner core typically contains fivehundred to three thousand fibers.
Many synthetic materials are available for such use including nylon, polyester, kevlar, zyex (polyetheretherketon), boron, and graphite fiber.
Various glue compositions are well-known in the art. A
common glue for synthetic fiber is nylon resin. After glueing, inner core 24 is cured, such as at 150 degrees C. for two minutes.
Inner core 24 is helically wrapped by a layer of larger strands 29 which form an outer core 28. If the outer core is formed by two or more layers of large strands, then adjacent layers are helically wound in 25 opposite directions. -~
As best seen in Figure 5, the string core 20 is processed by passing i* through a bath and die apparatus, denoted generally as 70. String core 20 is immersed in 30 a bath 72 of suitable molten ridge forming material, such -as nylon 71, and, upon exiting the bath 72 is passed thru a die 74 which leaves the desired nylon ridges 40 remaining. The nylon also acts as a glue, fills voids in the core, and forms a thin coating over the core. String 10 is than cooled, such as by water at 20 degrees C. The resulting string can be further processed, such as for moisture control or thermosetting, as desired.
. . ~ . ~ ' ' WO91/1l549 PCT/US90/01698 '210~93~3~
Ret~lrning once more to Figure 2, the results of the bath and die processing can be seen in cross-section.
- Nylon 71 from bath 72 acts as a glue and coating for the core 20. Extrusion die 74 has left ridges 40 bonded to the outside of the core and extending parallel axially with the string. In the exemplary embodiment of Figure 2, five evenly spaced ridges are shown. Ridges 40 are arc-shaped and project radially outward from core 20.
Ridge~ 40 impart more spin on a struck ball.
Preferably, ridges 40 may be circumscribed by a maximum diameter circle 90, shown in dashed line. Figure 2 is an enlarged view of a sting having a core 20 of 1.20 millimeters and a maximum diameter circle of 1.45 millimeters. Preferably, the largest maximum diameter circle is 1.70 millimeters.
The height, shape, and spacing of ridges 40 are important. Unless the maximum diameter circle 90 has a diameter 0.15 millimeters greater than the core, so that the ridges are at least 0.075 millimeters in height, the ridges are too small to be effective. Ridge heights of about 0.25 millimeters have been found to produce good 25 results. A core diameter of 1.00 - 1.30 millimeters with a maximum diameter circle of 1.35 - 1.70 millimeters has been found to impart superior spin without detracting from the other aspects of playability and therefore seems preferable.
The ridge radius is the outer arc of the ridge 40.
A ridge radius R of the difference between the radius of the maximum diameter circle 90 and the radius of the core 20 has been found to provide a desirable combination of good playing characteristics and ridge longevity. If the ridges 40 are too pointed on the outer end or too narrow in width, they are quickly worn down or damaged by play WO91/11s4s PCT/US90/01698 9 ~04~a7 and they loose their effectiveness. A large ridge radius is not as effective at spin enhancement and the added thickness of coating makes the string stiffer and less playable. ~oo large a ridge height makes the string difficult to string on a racquet and also adds to the string stiffness.
Preferably, between ridges,the glue coating over outer core 28 is of just sufficient thickness to prevent abrasion of the core structure during play and increase the contact area of the cross-over point, and therefore between ridges the outside of the coated string assumes the arc of the string core. The area where the ridges join the inner core coating is faired to add strenqth and prevent breakage of the ridges.
Also in Figure 2, ridged string lO is shown crossing over itself or another similar ridged string lOa having ridge 40a as strung on a racquet. The string contact ridges 42 increase the contact with the cross string lOa.
The larger contact area reduces the extent to which the strings will indent one another at the crossover point.
The indenting tends to weaken the strings and lowers elasticity. There i8 a sewing effect caused by the strings moving over one another as the ball is hit.
Sewing also wears, cuts and weakens strings. The larger contact area with the five ridge configuration lessens the sewing effect.
: '., The crossover points are the highest points on the face of the racquet and exert the greatest forces on the ball. With the five ridge configuration, at string cross-overs the strings assume the position shown in Figure 2.
This is a very stable position and is thought to prevent string lO from rotating when it encounters the ball.
Imparting spin to the ball applies rotational forces to the string. The better the string resists these .
, WO91/11549 PCI/l,lS90/01698 2~4~ 7 rotational forces the greater should be the spin on the ball.
Also, in the five ridge configuration, o~termost ridge 41 and both of the adjacent ridges are in good position to impart spin on a ball.
Alsoj although in the drawings the strings have been shown in cross-section at a string cross-over point and ridges have been designated as "outermost ridges~ and "ball contact ridges" or as "string contact ridges"; it should be clear that a given ridge may change from one to the other at adjacent cross-over points and , in fact, this seems desirable as the string does not thereby need to rotate.
Turning now to Figures 3 and 4 there is illustrated an alternate exemplary embodiment of ridged racquet string, denoted generally as 10', of the invention; this one having six ridges. Figure 3 is a perspective view of a segment of a six ridged string. Figure 4 is a slightly enlarged cross-sectional view of the six ridged string 10' of Figure 3 shown passing over a similar string lOa', such as while strung on a racquet.
The six ridged string 10' includes a core, denoted generally as 20', and a plurality of ridges 40' bonded to the core 20'. Ridges 40' are preferably evenly spaced, run axially with length of the string and are parallel to one another. Six ridged string 10' is produced the same - as the five ridged string except by use of a different die. "`
Turning now to Figure 4, the six ridged string 10' of Figure 3 is shown in cross-section with the addition of showing the string 10' as it crosses over a similar string lO'a such as it would in a strung racquet. In ~ ~ .
wO91/ll549 PCT/~IS90/01698 4~3~)7 11 `
this exemplary embodiment, the string core 20' is made also of construc~ion well-known in the art. Core 20' is comprised of a multiplicity of continuous large monofilaments 30 which are twisted and glued together to form the core 20'. There is no inner or outer core as in the exemplary five ridged string 10. ~-Figure 4 illustrates a core diameter of 1.30 millimeters and a maximum diameter circle 90' of 1.45 millimeters.
In the exemplary embodiment shown, ridges 40' are tooth-like in cross-section and project radially outward from core 20'. Preferably, toothed ridges 40' are about twice as wide as they are high for prevention of wear and breakage.
Six ridged string 10' also produces a large cross-over contact area which reduced indentation and sewing.
The two contact ridges 42' also help the string to resist rotation upon ball impact and upon imparting spin. The cross-over point of Figure 4 is simplified in that it does not show the true interme~hing of the strings lO',lOa' and their ridges 40',40a' in the strung condition. At cross-over, the string cores and ridges indent one another and the string cores and ridges protrude into the concavities between the ridges and core of the cross-over string. This intermeshing prevents rotation of the strings relative to one another.
~`Figure 6 illustrates another prefered embodiment of the invention. Figure 6 is a cross-sectional view of a racquet string 10" having four spaced ridges 40".
Core 20 is of conventional nature, such as illustrated ;35 and described heretofore with regard to Figures 1 - 4.
Glue, such as nylon resin 71, surrounds core 20 and forms rldges 40". Figure 6, illustrates a core diameter is , ' . . ', , , ~ ~ , ~
20~ `7 12 1.20 millimeters, and a maximum diameter circle of 1.70.
Thus, ridges 40" are 0.25 millimeters in height. Ridges 40", as illustrated, are triangular in shape with an apex angle of sixty degrees. Preferably, the apex angle S is less than ninety degrees. Too small an apex angle leads to rapid wear of the ridge, and an apex angle of about sixty degrees appears to be optimum. A truncated cone-shaped ridge of the same height wears better than the pointed ridge illustrated. Further testing is required to determine, for a given maximum diameter circle, under what conditions each produces the superior result.
As strung, two of the ridges 40", designated here as 42", are string contact ridges that will contact th~
cross-over tring. Considerable deformation of the string core and ridges occurs at cross-over. String contact ridges 42" interlock with the cross-over string string contact ridges and prevent the string 10" from rotation upon ball contact. The intermeshing of the ridges of the cross-over strings at the cross-over point is thought to reduce relative string movement. The intermeshing of string contact ridges 42" prevent the string from rotation upon ball contact such that the ball contact ridges 44" remain in position to impart maximum rotational force on the ball. The lac~ of rotation greatly reduces wear of the strings at the cross-over point.
..
In the four ridge example of Figure 6, ball contact ridges 44" are in particularly good position to impart spin on a ball coming from either direction relative to the string. That is a ball upon which spin i9 imposed will encounter one of the contact ridges first and with much greater force than the other ridge which is only incidentally contacted.
W09l/ll549 PCT/US90/01698 ~3~ ~
Fig~re 7 illustrates yet another exemplary embodiment of the ridged racquet string of the invention.
Figure 7 is a cross-sectional view similar to Figure 6 with a change in diameters and in number of ridges. The string 10"' of Figure 6 has an inner core 20 of l.00 millimeters and three ridges 40"' , each of height 0.275 ~ -millimeters, such that the string may be circumscribed by maximum diameter circle 90"' of 1.55 millimeters.
String contact ridges 42"' interlock with the string contact ridges of the cross-over string to prevent rotation. Ball contact ridge 44"' imparts spin on a ball approaching from either direction.
The string lO" with fo~r ridges appears to be lS particularly suited for several reasons. First, two of the ridges are always idealy spaced for intermeshing with the cross-over string, for providing a wide intermeshed contact base to prevent rotation. Second, the ball contact ridges are~thought to be located so as to provide maximum ball contact spin, i.e. at the outer "corners" of the string. Third, the 6tring need not rotate while str1nging the racguet. That is, at the seceeding cross-over point, the ball contact ridges simply become the strlng contact ridges and vice versa. This allows the 2S ball contact strings to always be in the desired positon.
For contra example, the three ridged string needs to be rotated between cross-over point~.
The ridged racquet string of the present invention will impart much more spin on the ball than conventional ` round or polygonal strings without noticeable loss of other desirable playability characteristics.
~ ~ .
Preliminary testing indicates that the ridged ~5 racquet string of the present invention will last over fifty percent longer than a similar round string. This appears to result primarily from the non-rotation of the . .
~ . .
c. -. ~ . . . ,} :-, ~
WO 91/1 1549 PCI/I,'S90/01698 '20~ ,! 14 string at cross-over.
Although the exemplary embodiments illustrate a fiber inner core 24 with an outer core 28 of multiple large monofilaments 29 helically wrapped around it, and core 20' of a multiplicity of large monofilaments, as will be seen, the invention is applicable other core ~-structures, such as an core of a single large monofilament surrounded by a wrapping.
' As used herein, the words rstring core" alone without further limitation applies to the string structure being inserted into the resin bath and die apparatus 70 and includes "core-Iess" string such as string formed by twisting together large monofilaments, or having a synthetic "fiber" core only with no outer core. The invention is also adaptable for use with natural fibers, such as gut, forming the string core.
;;,~ . .
Also, although in the drawings the strings have been shown in cross-section at a string cross-over point and ridges have been designated as ~ball contact ridges" or as ~string contact ridges~; it is reiterated that a given ridge may change from one to the other at adjacent cross- i over points and , in fact, this seems desirable as the string does not thereby need to rotate.
. : . .
Although particular embodiments of the invention have been illustrated and described, various changes may 30~ be made in the form, construction and arrangement of the elements herein without ~sacrificing any of its advantages. Therefore, it is to be understood that all matter herein is to bé interpreted as illustrative and not in any limiting sense and it is intended to cover in the appended claims such modifications and changes as come within the true spirit and scope of the invention.
.
,,: ., Ei~l~ Qf the Invention This invention relates in general to a sports racquet string and more specifically involves a string configuration that imparts more spin on the ball and to a method of manufacturing s~ch an improved string.
Background Qf the Inventlon The traditional and most popular cross-section of a sports racquet string is round. Such strings are made typically from natural gut (animal fiber) or from synthetic material,-such as nylon. Conventionally, strings are constructed by twisting many fine filaments of these materials together, with or without a center 20 filament, into a round core strand and then by passing `
the core strand through a round die to apply an outer layer coating.
In general, it is desirable that a string exhibit small damp~ng, that is low energy los~ and high resilience, and good elasticity, that is a low modulus of elasticity. These elements contribute to the playability -of the string. It is also desirable that the string be sufficiently durable.
The diameter of the string is very important as it affects the durability and playability of the string.
Generally, thin strings have superior playability. Thin strings exhibit high resilience and good elasticity, and they maintain longer contact with the ball for greater ;control. ~owever, thin strings may stretch and are more easily broken. On the other hand, thick strings are .
, WO91/11549 PCT/~'S90/0169X
28~ ; 2 stronger and more durable but lack the playability of thin strings.
An additional important characteristic of a string is its ability to impart spin on the ball. For ex,ample, in the game of tennis, a player standing behind the baseline would have to have a height of about six foot seven to see any of the opponent's court without looking thru the net. This means that most hard-hit balls passing over the net and not having forward spin will land out of bounds over the opponent's baseline. Ball spin affects the ball's flight characteristics. When a ball leaves the racquet string bed spinning forward, i.e.
rotating forward on top, it's flight path will tend to curve downward, and it will land earlier and bounce lower. With good top spin, a player can hit a given ball much harder and still have the ball land in. When a ball leaves the racquet string bed spinning backward, i.e.
rotating forward on bottom, its flight path is flatter;
it will tend to land further and bounce higher. Thus, if the player can control spin, the player can control to some degree the trajectory of the ball to advantage.
Again, string characteristics largely determine the amount of spin that can be imparted on the ball. As previously mentioned, the amount of string elongation and resilience determines the amount of time the strings are in contact with the ball. Generally, the thinner the string, the~ greater the contact time. When the ball impacts on the racquet face, the ball remains in contact with the string bed for about three to five thousandths o~f a second. ~During this time, the player is able to impose more control over the direction of ball return and is able to impart spin to the ball to control its flight characteristics.
To put spin on the ball, the ball is struck with the .
:~' : .' .. :
~: :
`~::: : :
:
W091/11549 PCT/~'S90/01698 ~Q49~
', -.
-racket face at an angle to the flight path and the racket face is moved in the plane of the face. Increasing the friction between the strings and the hall has been thought to enhance imparting spin on the ball.
' Synthetic fiber strings, in particular, are excessively smooth in their outer surface and tend to slip over the ball. Many measures have been taken to enhance friction including: roughening t`ne outer surface of the string such as by grinding with abrasives, surface coating the string with frictional or rubbery substances, -twisting or braiding fiber multifiliments, and winding of silk yarns around the string core.
15Synthetic strings treated in the above-described manners tend to have poor dimensional stability and are reduced in strength and elasticity resulting in tension 1088 during play. Further, some are inferior in durability because they exhibit surface aberrations, wearings or breakages due to degredation of the resins, and abrasion, peeling or denaturing of the treating substances. Moreover, since the above-mentioned treatment6 constitute additional 6teps in manufacture, there is an increase in production costs.
Another proposed method to increase string friction is the use of string of polygonal c~oss-section whereby the sharp corners resulting at the juncture of the faces of the polygon are the spin enhancing portions. Two types of polygonal-shaped string have been proposed.
Reta, U.S. Patent No. 4,805,393 proposes the use of a -multi-sided cross-sectional configuration string; Wells, U.S~ Patent No. 4,860,531, proposes a polygonal coating over a round central core.
; Traditional round strings may have a thin, evenly distributed coatin5 around the core to provide protection ::
~ ' . .
:
to the core strands which provide the tensile strength and playability of the string.
As two round strings .cross over one another, due to the very small contact area they weaken one another by indenting one another and by cutting one another in a sawing action as the strings move relative to one another during play. ;
Therefore, it is desirable to have an improved sports racquet string having much better spin-imparting characteristics than a conventional round string and which achieves this without significant loss in playability.
It is further desirable, that such a string reduce the weakening characteristics of string cross-over and therefore be more durable than conventional strings.
-S~M~ARY OF T~ INV~RTION
According to the invention, a string for a sports racquet, such as a tennis racquet string, is comprised of a core having a plurality of ridges thereon for aiding in imparting spin on a ball. The ridges are parallel to one another and extend axially with the string. Preferably, the inner core has a diameter of l.00 - 1.30 millimeters.
ireferably, the ridges are of approximately 0.25 millimeters in height. Preferably, the ridges can be circumscribed by a circle of 1.70 millimeters.
` ~ The process for making the ridged string includes passing a string core through a bath of resin, such as :
nylon, for coating and glueing the core and then through a die shaped so as to form the ridges.
, ~
', WO91/11s4s ~ O~ PCT/US90/01698 Preferably the size, spacing, and number of the ridges increase contact area between strings at the cross-over points and add to the stability to prevent string rotation and movement relative to one another.
Other features and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout.
:: -BRIFF DESCRIPTION OF T~E DRAHING
Figure 1 is a perspective view of a segment of aprefered embodiment of the ridged racquet string of the invention.
Figure 2 i8 a slightly enlarged cross-sectional view of the string of Figure 1 shown passing over a similar string, such as while strung on a racquet.
Figure 3 is a perspective view of a segment of an alternate exemplary embodiment of the ridged racquet string of the invention.
Figure 4 is a slightly enlarged cross-sectional view i~ 30 of the ridged string of Figure 3 shown passing over a ~ similar string, such as while strung on a racquet.
i -~ .
Figure 5 is a view of the extrusion step in the manufacture of the ridged string of the invention.
- ` Figure 6 is a cross-sectional view of an alternate ~ -preferred embodiment of the ridged racquet string of the :`~
WO91/lIS49 PCT/US90/01698 ~ \37 invention; this one having four triangular ridges.
Fig~re 7 is a cross-sectional view of another alternate exemplary embodiment of the ridged racquet string of the invention; this one having three triangular ridges.
DXTAILED D~SCRIPTION OF T~E INVENTION
With reference now to the drawing, and more particularly to Figure 1 thereof, there is shown, in perspective view, a segment of a prefered embodiment of the ridged sports racquet string, denoted generally as 10, of the present invention. Ridged string lC includes a core, denoted generally as 20, and a plurality of ridges 40 bonded to the core 20. Ridges 40 run axially with length of the string and are parallel to one another.
.
Turning now to Figure 2, the ridged string 10 of Figure 1 i8 shown in cross-6ection with the addition of showing the string 10 as it cros6e6 over a similar string 10a such as it would in a strung racquet. The cross-over point of-Figure 2 is simplified in that it does not show the true intermeshing of the strings 10,10a and their ridges 40,40a in the strung condition. At cross-over, the string cores and ridges indent one another and the string cores and ridges protrudé into the concavities between the ridges and core of the cross-over string.
This intermeshing prevents rotation of the strings relative to one another.
~:
In the prefered embodiment shown, the string core 20 is made of construction well-known in the art. Core 20 is of synthetic material and is of composite construction .
::~
wo91/1l5~9 PCT/~'S90/0169X
)7 comprising an inner core 24 and and an outer core 28.
An inner core can be a thick extruded monofilament or be of the "fiber" type. Inner core 24, shown,is of the "fiber" type and comprises a multiplicity of of small diameter monofilament fibers or strands which are twisted and glued together to form the inner core structure. The small monofilament fibers need not be continuous as the friction of the package prevents slippage. In cross-section, a fiber inner core typically contains fivehundred to three thousand fibers.
Many synthetic materials are available for such use including nylon, polyester, kevlar, zyex (polyetheretherketon), boron, and graphite fiber.
Various glue compositions are well-known in the art. A
common glue for synthetic fiber is nylon resin. After glueing, inner core 24 is cured, such as at 150 degrees C. for two minutes.
Inner core 24 is helically wrapped by a layer of larger strands 29 which form an outer core 28. If the outer core is formed by two or more layers of large strands, then adjacent layers are helically wound in 25 opposite directions. -~
As best seen in Figure 5, the string core 20 is processed by passing i* through a bath and die apparatus, denoted generally as 70. String core 20 is immersed in 30 a bath 72 of suitable molten ridge forming material, such -as nylon 71, and, upon exiting the bath 72 is passed thru a die 74 which leaves the desired nylon ridges 40 remaining. The nylon also acts as a glue, fills voids in the core, and forms a thin coating over the core. String 10 is than cooled, such as by water at 20 degrees C. The resulting string can be further processed, such as for moisture control or thermosetting, as desired.
. . ~ . ~ ' ' WO91/1l549 PCT/US90/01698 '210~93~3~
Ret~lrning once more to Figure 2, the results of the bath and die processing can be seen in cross-section.
- Nylon 71 from bath 72 acts as a glue and coating for the core 20. Extrusion die 74 has left ridges 40 bonded to the outside of the core and extending parallel axially with the string. In the exemplary embodiment of Figure 2, five evenly spaced ridges are shown. Ridges 40 are arc-shaped and project radially outward from core 20.
Ridge~ 40 impart more spin on a struck ball.
Preferably, ridges 40 may be circumscribed by a maximum diameter circle 90, shown in dashed line. Figure 2 is an enlarged view of a sting having a core 20 of 1.20 millimeters and a maximum diameter circle of 1.45 millimeters. Preferably, the largest maximum diameter circle is 1.70 millimeters.
The height, shape, and spacing of ridges 40 are important. Unless the maximum diameter circle 90 has a diameter 0.15 millimeters greater than the core, so that the ridges are at least 0.075 millimeters in height, the ridges are too small to be effective. Ridge heights of about 0.25 millimeters have been found to produce good 25 results. A core diameter of 1.00 - 1.30 millimeters with a maximum diameter circle of 1.35 - 1.70 millimeters has been found to impart superior spin without detracting from the other aspects of playability and therefore seems preferable.
The ridge radius is the outer arc of the ridge 40.
A ridge radius R of the difference between the radius of the maximum diameter circle 90 and the radius of the core 20 has been found to provide a desirable combination of good playing characteristics and ridge longevity. If the ridges 40 are too pointed on the outer end or too narrow in width, they are quickly worn down or damaged by play WO91/11s4s PCT/US90/01698 9 ~04~a7 and they loose their effectiveness. A large ridge radius is not as effective at spin enhancement and the added thickness of coating makes the string stiffer and less playable. ~oo large a ridge height makes the string difficult to string on a racquet and also adds to the string stiffness.
Preferably, between ridges,the glue coating over outer core 28 is of just sufficient thickness to prevent abrasion of the core structure during play and increase the contact area of the cross-over point, and therefore between ridges the outside of the coated string assumes the arc of the string core. The area where the ridges join the inner core coating is faired to add strenqth and prevent breakage of the ridges.
Also in Figure 2, ridged string lO is shown crossing over itself or another similar ridged string lOa having ridge 40a as strung on a racquet. The string contact ridges 42 increase the contact with the cross string lOa.
The larger contact area reduces the extent to which the strings will indent one another at the crossover point.
The indenting tends to weaken the strings and lowers elasticity. There i8 a sewing effect caused by the strings moving over one another as the ball is hit.
Sewing also wears, cuts and weakens strings. The larger contact area with the five ridge configuration lessens the sewing effect.
: '., The crossover points are the highest points on the face of the racquet and exert the greatest forces on the ball. With the five ridge configuration, at string cross-overs the strings assume the position shown in Figure 2.
This is a very stable position and is thought to prevent string lO from rotating when it encounters the ball.
Imparting spin to the ball applies rotational forces to the string. The better the string resists these .
, WO91/11549 PCI/l,lS90/01698 2~4~ 7 rotational forces the greater should be the spin on the ball.
Also, in the five ridge configuration, o~termost ridge 41 and both of the adjacent ridges are in good position to impart spin on a ball.
Alsoj although in the drawings the strings have been shown in cross-section at a string cross-over point and ridges have been designated as "outermost ridges~ and "ball contact ridges" or as "string contact ridges"; it should be clear that a given ridge may change from one to the other at adjacent cross-over points and , in fact, this seems desirable as the string does not thereby need to rotate.
Turning now to Figures 3 and 4 there is illustrated an alternate exemplary embodiment of ridged racquet string, denoted generally as 10', of the invention; this one having six ridges. Figure 3 is a perspective view of a segment of a six ridged string. Figure 4 is a slightly enlarged cross-sectional view of the six ridged string 10' of Figure 3 shown passing over a similar string lOa', such as while strung on a racquet.
The six ridged string 10' includes a core, denoted generally as 20', and a plurality of ridges 40' bonded to the core 20'. Ridges 40' are preferably evenly spaced, run axially with length of the string and are parallel to one another. Six ridged string 10' is produced the same - as the five ridged string except by use of a different die. "`
Turning now to Figure 4, the six ridged string 10' of Figure 3 is shown in cross-section with the addition of showing the string 10' as it crosses over a similar string lO'a such as it would in a strung racquet. In ~ ~ .
wO91/ll549 PCT/~IS90/01698 4~3~)7 11 `
this exemplary embodiment, the string core 20' is made also of construc~ion well-known in the art. Core 20' is comprised of a multiplicity of continuous large monofilaments 30 which are twisted and glued together to form the core 20'. There is no inner or outer core as in the exemplary five ridged string 10. ~-Figure 4 illustrates a core diameter of 1.30 millimeters and a maximum diameter circle 90' of 1.45 millimeters.
In the exemplary embodiment shown, ridges 40' are tooth-like in cross-section and project radially outward from core 20'. Preferably, toothed ridges 40' are about twice as wide as they are high for prevention of wear and breakage.
Six ridged string 10' also produces a large cross-over contact area which reduced indentation and sewing.
The two contact ridges 42' also help the string to resist rotation upon ball impact and upon imparting spin. The cross-over point of Figure 4 is simplified in that it does not show the true interme~hing of the strings lO',lOa' and their ridges 40',40a' in the strung condition. At cross-over, the string cores and ridges indent one another and the string cores and ridges protrude into the concavities between the ridges and core of the cross-over string. This intermeshing prevents rotation of the strings relative to one another.
~`Figure 6 illustrates another prefered embodiment of the invention. Figure 6 is a cross-sectional view of a racquet string 10" having four spaced ridges 40".
Core 20 is of conventional nature, such as illustrated ;35 and described heretofore with regard to Figures 1 - 4.
Glue, such as nylon resin 71, surrounds core 20 and forms rldges 40". Figure 6, illustrates a core diameter is , ' . . ', , , ~ ~ , ~
20~ `7 12 1.20 millimeters, and a maximum diameter circle of 1.70.
Thus, ridges 40" are 0.25 millimeters in height. Ridges 40", as illustrated, are triangular in shape with an apex angle of sixty degrees. Preferably, the apex angle S is less than ninety degrees. Too small an apex angle leads to rapid wear of the ridge, and an apex angle of about sixty degrees appears to be optimum. A truncated cone-shaped ridge of the same height wears better than the pointed ridge illustrated. Further testing is required to determine, for a given maximum diameter circle, under what conditions each produces the superior result.
As strung, two of the ridges 40", designated here as 42", are string contact ridges that will contact th~
cross-over tring. Considerable deformation of the string core and ridges occurs at cross-over. String contact ridges 42" interlock with the cross-over string string contact ridges and prevent the string 10" from rotation upon ball contact. The intermeshing of the ridges of the cross-over strings at the cross-over point is thought to reduce relative string movement. The intermeshing of string contact ridges 42" prevent the string from rotation upon ball contact such that the ball contact ridges 44" remain in position to impart maximum rotational force on the ball. The lac~ of rotation greatly reduces wear of the strings at the cross-over point.
..
In the four ridge example of Figure 6, ball contact ridges 44" are in particularly good position to impart spin on a ball coming from either direction relative to the string. That is a ball upon which spin i9 imposed will encounter one of the contact ridges first and with much greater force than the other ridge which is only incidentally contacted.
W09l/ll549 PCT/US90/01698 ~3~ ~
Fig~re 7 illustrates yet another exemplary embodiment of the ridged racquet string of the invention.
Figure 7 is a cross-sectional view similar to Figure 6 with a change in diameters and in number of ridges. The string 10"' of Figure 6 has an inner core 20 of l.00 millimeters and three ridges 40"' , each of height 0.275 ~ -millimeters, such that the string may be circumscribed by maximum diameter circle 90"' of 1.55 millimeters.
String contact ridges 42"' interlock with the string contact ridges of the cross-over string to prevent rotation. Ball contact ridge 44"' imparts spin on a ball approaching from either direction.
The string lO" with fo~r ridges appears to be lS particularly suited for several reasons. First, two of the ridges are always idealy spaced for intermeshing with the cross-over string, for providing a wide intermeshed contact base to prevent rotation. Second, the ball contact ridges are~thought to be located so as to provide maximum ball contact spin, i.e. at the outer "corners" of the string. Third, the 6tring need not rotate while str1nging the racguet. That is, at the seceeding cross-over point, the ball contact ridges simply become the strlng contact ridges and vice versa. This allows the 2S ball contact strings to always be in the desired positon.
For contra example, the three ridged string needs to be rotated between cross-over point~.
The ridged racquet string of the present invention will impart much more spin on the ball than conventional ` round or polygonal strings without noticeable loss of other desirable playability characteristics.
~ ~ .
Preliminary testing indicates that the ridged ~5 racquet string of the present invention will last over fifty percent longer than a similar round string. This appears to result primarily from the non-rotation of the . .
~ . .
c. -. ~ . . . ,} :-, ~
WO 91/1 1549 PCI/I,'S90/01698 '20~ ,! 14 string at cross-over.
Although the exemplary embodiments illustrate a fiber inner core 24 with an outer core 28 of multiple large monofilaments 29 helically wrapped around it, and core 20' of a multiplicity of large monofilaments, as will be seen, the invention is applicable other core ~-structures, such as an core of a single large monofilament surrounded by a wrapping.
' As used herein, the words rstring core" alone without further limitation applies to the string structure being inserted into the resin bath and die apparatus 70 and includes "core-Iess" string such as string formed by twisting together large monofilaments, or having a synthetic "fiber" core only with no outer core. The invention is also adaptable for use with natural fibers, such as gut, forming the string core.
;;,~ . .
Also, although in the drawings the strings have been shown in cross-section at a string cross-over point and ridges have been designated as ~ball contact ridges" or as ~string contact ridges~; it is reiterated that a given ridge may change from one to the other at adjacent cross- i over points and , in fact, this seems desirable as the string does not thereby need to rotate.
. : . .
Although particular embodiments of the invention have been illustrated and described, various changes may 30~ be made in the form, construction and arrangement of the elements herein without ~sacrificing any of its advantages. Therefore, it is to be understood that all matter herein is to bé interpreted as illustrative and not in any limiting sense and it is intended to cover in the appended claims such modifications and changes as come within the true spirit and scope of the invention.
Claims (23)
1. A string for a sports racquet comprising:
an elastic, resilient string core of high tensile strength; and a plurality of axially extending parallel ridges of synthetic material bonded to said string core; such that in cross-section:
said string core is substantially circular with a diameter of 1.00 - 1.30 millimeters; and said ridges are radial protrusions on said core, the outermost projections of which may be circumscribed by a circle of 1.70 millimeters diameter.
an elastic, resilient string core of high tensile strength; and a plurality of axially extending parallel ridges of synthetic material bonded to said string core; such that in cross-section:
said string core is substantially circular with a diameter of 1.00 - 1.30 millimeters; and said ridges are radial protrusions on said core, the outermost projections of which may be circumscribed by a circle of 1.70 millimeters diameter.
2. The string of Claim 1 wherein said ridges are greater than 0.075 millimeters in height.
3. The string of Claim 1 wherein said ridges are six in number.
4. The string of Claim 3 wherein said ridges are evenly spaced about said string core.
5. The string of Claim 1 wherein said ridges are five in number.
6. The string of Claim 5 wherein said ridges are evenly spaced about said string core.
7. The string of Claim 1 wherein said ridges in cross-section are arc-shaped.
8. The string of Claim 1 wherein said ridges in cross-section are generally arc-shaped with a ridge arc radius of 0.075 millimeters or greater.
9. The string of Claim 1 wherein said ridges in cross-section are substantially rectangular.
10. The string of Claim 1 wherein said ridges in cross-section are substantially rectangular with a width of twice the height.
11. The string of Claim 1 wherein said ridges are three to eight in number.
12. The string of Claim 1 wherein said ridges are evenly spaced about said string core.
13. The string of Claim 1 wherein said ridges in cross-section are substantially triangular.
14. The string of Claim 13 wherein said ridges are four in number.
15. The string of CLaim 13 wherein said ridges have an apex angle of less than ninety degrees.
16. The string of Claim 13 wherein said ridges are evenly spaced about said string core.
17. The string of Claim 13 wherein said ridges are three in number.
18. The string of Claim 1 wherein said string core comprises:
an inner core of twisted and glued monofilament strands; and an outer core comprising a plurality of larger diameter strands helically wound about said inner core.
an inner core of twisted and glued monofilament strands; and an outer core comprising a plurality of larger diameter strands helically wound about said inner core.
19. A string for a sports racquet comprising:
an elastic, resilient string core of high tensile strength; and a plurality of axially extending parallel ridges of synthetic material bonded to said string core; such that in cross-section:
said string core is substantially circular with a diameter of 1.00 - 1.35 millimeters; and said ridges are radial protrusions on said core and have a height of greater than 0.075 millimeters.
an elastic, resilient string core of high tensile strength; and a plurality of axially extending parallel ridges of synthetic material bonded to said string core; such that in cross-section:
said string core is substantially circular with a diameter of 1.00 - 1.35 millimeters; and said ridges are radial protrusions on said core and have a height of greater than 0.075 millimeters.
20. The string of Claim 19 wherein said ridges are four in number and are evenly spaced about said string.
21. The string of Claim 19 wherein said ridges are substantially triangular in cross-section.
22. The string of Claim 21 wherein said ridges have an apex angle of less than ninty degrees.
23. A method for the production of a ridged string for a sports racquet comprising:
forming a string core of elastic, resilient, tensilely strong, material;
processing said string core so as to create a plurality of axially extending parallel ridges of synthetic material bonded to said string core including passing the string core through a bath of the ridge material and through and extrusion die.
forming a string core of elastic, resilient, tensilely strong, material;
processing said string core so as to create a plurality of axially extending parallel ridges of synthetic material bonded to said string core including passing the string core through a bath of the ridge material and through and extrusion die.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US47070690A | 1990-01-26 | 1990-01-26 | |
| US470,706 | 1990-01-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2049307A1 true CA2049307A1 (en) | 1991-07-27 |
Family
ID=23868695
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002049307A Abandoned CA2049307A1 (en) | 1990-01-26 | 1990-03-30 | Ridged racquet string |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0465605A4 (en) |
| AU (1) | AU634937B2 (en) |
| CA (1) | CA2049307A1 (en) |
| WO (1) | WO1991011549A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1994021332A1 (en) * | 1993-03-17 | 1994-09-29 | Kosmin, Gerald, Emmanuel | Sports racket string |
| FR2705902B1 (en) * | 1993-06-01 | 1995-07-21 | Turquety Maurice | Ribbed tennis string. |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1225120A (en) * | 1959-02-19 | 1960-06-29 | Patent & Verwaltungs A G | Plastic clothesline |
| US4306410A (en) * | 1980-11-12 | 1981-12-22 | Kureha Kagaku Kogyo Kabushiki Kaisha | String construction for athletic rackets |
| JPS6077776A (en) * | 1983-10-03 | 1985-05-02 | 株式会社ゴーセン | Gut |
| DE3447608A1 (en) * | 1984-12-28 | 1986-07-03 | F. Kleinekathöfer KG, 8207 Endorf | Tennis string |
| US4805393A (en) * | 1986-11-20 | 1989-02-21 | Reta Marcos A | String construction for a sports racket |
| US4860531A (en) * | 1987-12-16 | 1989-08-29 | Wells D Phillips | Racquet strings |
-
1990
- 1990-03-30 WO PCT/US1990/001698 patent/WO1991011549A1/en not_active Application Discontinuation
- 1990-03-30 EP EP19900907941 patent/EP0465605A4/en not_active Withdrawn
- 1990-03-30 CA CA002049307A patent/CA2049307A1/en not_active Abandoned
- 1990-03-30 AU AU55681/90A patent/AU634937B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| AU634937B2 (en) | 1993-03-04 |
| EP0465605A1 (en) | 1992-01-15 |
| EP0465605A4 (en) | 1992-06-03 |
| WO1991011549A1 (en) | 1991-08-08 |
| AU5568190A (en) | 1991-08-21 |
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