The embodiments of the present invention will be described below with reference to the drawings.
Rackets of the embodiments which will be described below are regulation-ball tennis rackets. In the embodiments described below, the longitudinal string and the transverse string are stretched in parallel with the longitudinal direction of the racket frame and the widthwise direction thereof respectively. The left part and the right part of the racket frame are symmetrical with respect to the longitudinal axis drawn from the apex of the ball-hitting face to the center of the gripping part.
In the racket 10, as shown in
The racket frame 11 is composed of a tubular body made of fiber reinforced prepreg sheets. The racket frame 11 has a head part 12, a throat part 11, a shaft part 14, and a grip part 15. These parts are continuously formed. The throat part 13 connecting the head part 12 and the shaft part 14 to each other is bifurcated. A yoke part 16 is formed between a pair of the left and right throat parts 13. A string-stretching part surrounding a ball-hitting face F is constructed of the yoke part 16 and the head part 12.
As shown in
As shown in
As shown in
The extended longitudinal string holes 21-1 are formed in penetration through the racket frame 11, with axes L3-1 thereof almost parallel with the longitudinal axis L1 of the racket frame 11.
More specifically, the extended longitudinal string holes 21-1 are formed in penetration through the racket frame 11 in the range from the connection portion 17 to the peripheral surface of the throat part 13 with the extended longitudinal string holes 21-1 inclining at ±1° to the longitudinal axis L1 of the racket frame 11. Thus the inner holes 21a are formed on an inner peripheral surface of the connection portion 17, whereas elliptic outer holes 21b are formed on the peripheral surface of the throat part 13.
As shown in
The size of the inner hole 21a of the longitudinal string hole 21 (including the extended longitudinal string hole 21-1) and that of the inner hole 22a of the transverse string hole 22 are so set that there is a gap between the longitudinal string 41 passing through the inner hole 21a and the periphery of the inner hole 21a to allow the longitudinal string 41 to be displaceable in the gap and that there is a gap between the transverse string 42 passing through the inner hole 22a and the periphery of the inner hole 22a to allow the transverse string 42 to be displaceable in the gap.
In tensionally mounting the longitudinal string 41 and the transverse string 42 on the racket frame 11, a string protection member 31, shown in
The string protection member 31 is composed of a plurality of grommets 32 having insertion through-holes 32a through which the strings 41, 42 are inserted and the bumper 33 connecting the base portions of the grommets 32 to each other, with the base portions of the grommets 32 projecting inward. The string protection member 31 can be made of thermoplastic resin or thermosetting resin. Nylon resin and urethane resin are favorable because these resins allow the string protection member 31 to have a high strength and flexibility. In this respect, the nylon resin is especially favorable.
In the racket frame 11 having the above-described construction, the total (N1) of the string holes 20 is set to 64. All of the string holes are the vertical and transverse string holes 21, 22 formed in penetration through the racket frame 11, with the longitudinal string hole 21 parallel with the longitudinal axis L1 or almost parallel therewith, namely, inclining at ±1° thereto and with the transverse string hole 22 parallel with the widthwise direction L2 or almost parallel therewith, namely, inclining at ±1° thereto. The total of the vertical and transverse string holes 21, 22 is denoted as Ns1.
In the racket 10 of the first embodiment, the longitudinal strings 41 are mounted on the racket frame 11 by stretching them in the direction parallel with the longitudinal axis L1 of the racket frame 11 and in the direction parallel with the widthwise direction L2 of the racket frame 11 respectively. Therefore on the ball-hitting face F, the axis L3 of each of the longitudinal string holes 21 aligns or almost aligns (inclines at ±1°) with the stretched direction of the longitudinal strings 41 passing therethrough. Similarly on the ball-hitting face F, the axis L4 of each of the transverse string holes 22 aligns or almost aligns (inclines at ±1°) with the stretched direction of the transverse strings 42 passing therethrough. Supposing that the total of the vertical and transverse string holes 21, 22 is Ns2, Ns1=Ns2, and the value of Ns1/N1 and that of Ns2/N2 are 1.0.
Therefore each of the 14 vertical strings 41 stretched on the ball-hitting face F has its deformation support point at its both ends fixed to the outer edge of two (upper and lower) outer openings 21b of each longitudinal string hole 21. Similarly each of the 18 transverse strings 42 stretched on the ball-hitting face F has its deformation support point at its both ends fixed to the outer edge of two (left and right) outer openings 22b of the transverse string hole 22. These vertical and transverse strings 41 and 42 are hereinafter referred to as “the string A having its deformation support point at its both ends fixed to the outer edge of the outer openings of the string hole”.
Because the effective length of all of the strings stretched on the ball-hitting face F is set large, the strings have improved restitution performance in a large area in various directions around the center of the ball-hitting face F. Therefore the sweet area can be enlarged in a favorable balance in various directions.
The extended longitudinal string holes 21-1 are formed in the range from the connection portion 17 to the throat part 13, with the extended longitudinal string holes 21-1 approximately parallel with the longitudinal axis L1 of the racket frame 11 so that the longitudinal string 41 comes in contact with only the outer hole 21b. Therefore the effective length of each longitudinal string can be increased by the length of the corresponding extended longitudinal string hole 21-1. Owing to the formation of the extended longitudinal string holes 21-1, it is possible to greatly enhance the restitution performance of the sweet area at the left and right sides thereof.
In the second embodiment, the number of the longitudinal strings 41 is increased by two by disposing them at the left and right ends of longitudinal strings 41. Thus the total of the number of the longitudinal strings 41 is 16. 16 longitudinal strings 41 and 18 transverse strings 42 are mounted on the racket frame 11 by stretching them in penetration through 68 (N1, N2=68) string holes 20 (21, 22, 23, 24).
As shown in
An axis L7 of each of four string holes formed in penetration through the racket frame 11 at the top side and the grip side thereof to receive the upper-end transverse string 42 and the lower-end transverse string 42 is vertical to an tangent L8 to the inner peripheral surface of the racket frame 11. The four string holes are denoted as inclined string holes 24.
Except the inclined string holes 23, 24, the longitudinal string holes 21 and the transverse string holes 42 through which the longitudinal strings 41 and the transverse strings 42 are inserted respectively are the same as those of the racket of the first embodiment.
Similarly to the first embodiment, three extended longitudinal string holes 21-1 formed in penetration through each of the left and right connection portions 17 are almost parallel with the longitudinal axis L1 of the racket frame 11, i.e., inclines at ±1° thereto.
In the second embodiment, the total N1 of the string holes 20 is 68. The total (Ns1) of the longitudinal and transverse strings 21, 22 is 60. Therefore the value of Ns1/N1 is 0.88.
In the second embodiment, the greater part (30 strings) of all the strings (34 strings) is the string A having its deformation support point at its both ends fixed to the outer edge of the outer openings of the string hole. Therefore the racket frame 11 has an improved restitution performance and a large sweet area.
In the racket 10 of the second embodiment, the longitudinal strings 41 and the transverse strings 42 are mounted on the racket frame 11 by stretching them in the direction parallel with the longitudinal axis L1 of the racket frame 11 and in the direction parallel with the widthwise direction L2 of the racket frame 11 respectively. Therefore on the ball-hitting face F, the axis L3 of each of the longitudinal string holes 21 aligns or almost aligns (inclines at ±1°) with the stretched direction of the longitudinal strings 41 passing therethrough. Similarly on the ball-hitting face F, the axis L4 of each of the transverse string holes 22 aligns or almost aligns (inclines at ±1°) with the stretched direction of the transverse strings 42 passing therethrough. Therefore Ns2/N2 is 0.88 equal to the above-described Ns1/N1.
In the third embodiment, similarly to the second embodiment, the total of the number of the longitudinal strings 41 is 16, and the total of the number of the transverse strings 42 is 18. The 34 longitudinal and transverse strings are mounted on the racket frame 11 by stretching them in penetration through 68 (N1, N2=68) string holes 20 (21, 22, 23, 24).
The racket frame 11 has eight inclined string holes 23, disposed at the top side thereof, into which eight (four left-end strings and four right-end strings) longitudinal strings 41 disposed at the left and right sides of the racket frame 11 are inserted respectively and two inclined string holes 23, disposed at the grip side thereof, into which the left-end and right-end longitudinal strings 41 are inserted respectively.
The racket frame 11 has four inclined string holes 24, disposed at the top side thereof, into which two transverse strings 42 are inserted respectively and six inclined string holes 24, disposed at the grip side thereof, into which three transverse strings 42 are inserted respectively.
Except the inclined string holes 23, 24, the longitudinal string holes 21 and the transverse string holes 22 are the same as those of the first embodiment.
Similarly to the first embodiment, three extended longitudinal string holes 21-1 formed in penetration through each of the left and right connection portions 17 are almost parallel with the longitudinal axis L1 of the racket frame 11, i.e., inclines at ±1° thereto.
In the third embodiment, the total of the string holes is 68 (=N1). The total (Ns1) of the longitudinal and transverse strings 21, 22 is 48. Therefore the value of Ns1/N1 is 0.71.
In the third embodiment, some of 24 strings which exceeds 70% of the total, namely, 34 strings are the string A having its deformation support point at its both ends fixed to the outer edge of the outer openings of the string hole. Some of 24 strings are strings B having deformation support point disposed at its one end fixed to the outer edge of the outer opening of the string hole. Because the variable length of the string A or the string B is long, the racket frame is capable of having improved restitution performance and an increased sweet area.
In the racket of the third embodiment, the longitudinal strings 41a and the transverse strings 42a are mounted on the racket frame 11 by stretching them in the direction parallel with the longitudinal axis L1 of the racket frame 11 and in the direction parallel with the widthwise direction L2 of the racket frame 11 respectively. Therefore on the ball-hitting face F, the axis L3 of each of the 22 longitudinal string holes 21 aligns or almost aligns (inclines at ±1°) with the stretched direction of the longitudinal strings 41a passing therethrough. Similarly on the ball-hitting face F, the axis L4 of each of the 26 transverse string holes 22 aligns or almost aligns (inclines at ±1°) with the stretched direction of the transverse strings 42a passing therethrough. Therefore Ns2/N2 is 0.71 equal to the above-described Ns1/N1.
As shown in table 1, a tennis racket of each of examples 1 through 4 and a comparison example 1 was formed. The total (Ns) of the longitudinal string holes and the transverse string holes, the total (N) of the string holes, the value of Ns/N, and the configurations of the longitudinal string holes formed at the connection portion 17 were differentiated from one another respectively. The coefficient of restitution of each tennis racket was measured at different hitting points on the ball-hitting face F.
The total Ns of the longitudinal and transverse string holes shown in table 1 corresponds to Ns1. The longitudinal and transverse strings were inserted through the longitudinal and transverse string holes respectively without inclining the longitudinal and transverse strings to the axial direction of the longitudinal and transverse string holes. Therefore in any of the racket frame of each of the examples 1 through 4 and the comparison example 1, Ns1=Ns2.
The racket frames of the examples 1 through 4 and the comparison example 1 were made of fiber reinforced thermoplastic resin and hollow and had the same configuration. The area of the ball-hitting face F was set to 110 square inches. The whole length of the racket frame was set to 27 inches (699 mm). The weight of the racket frame and the racket frame balance were set as shown in table 1.
More specifically, prepreg sheets made of the fiber reinforced resin composed of carbon fibers serving as the reinforcing fiber thereof and epoxy resin serving as the matrix thereof were layered at angles of 0°, 22°, 30°, 45° and 90° on a mandrel coated with a pressurized tube made of nylon 66 to form a vertical laminate of the prepreg sheets. After the mandrel was removed from the laminate, the laminate was set in a die. The die was clamped and heated to 150° for 30 minutes, with an air pressure of 9 kgf/cm2 kept applied to the inside of the pressurized tube to form the racket frame of each of the examples and comparison examples.
In the racket frame of each of the examples 1 through 4 and the comparison example 1, the longitudinal string was tensionally fastened thereto in parallel with the longitudinal axis L1 thereof whereas the transverse string 42 was tensionally fastened thereto in parallel with the widthwise direction L2 thereof.
The racket frame had the same construction as that of the racket frame of the first embodiment. More specifically, the racket frame had 64 string holes consisting of 28 longitudinal string holes 21 and 36 transverse string holes 22. Thus Ns/N was 1.0.
Three longitudinal string holes were formed as the extended longitudinal string holes 21-1 at each of the left and right connection portions 17 adjacent to the yoke part 16 and the left and right portions of the throat part 13 by extending the longitudinal string holes 21 to the peripheral surface of the throat part 13.
The racket frame of the example 2 had the same construction as that of the second embodiment. That is, of 68 string holes, four inclined string holes 23 were formed at the top side of the racket frame and the grip side thereof to receive a left-end longitudinal string and a right-end longitudinal string, and four inclined string holes 24 were formed at the left side of the racket frame and the right side thereof to receive an upper-end transverse string and a lower-end transverse string. 60 string holes were formed as longitudinal and transverse strings 21 and 22. The value of Ns1/N1 was 0.88. The other constructions were the same as those of the example 1.
The racket frame of the example 3 had the same construction as that of the third embodiment. That is, the racket frame had 68 string holes. The racket frame 11 had eight inclined string holes 23, disposed at the top side thereof, into which four left-side longitudinal strings 41 and four right-side longitudinal strings 41 are inserted respectively; two string holes 23, disposed at the grip side thereof, into which one left-end longitudinal string and one right-end longitudinal string are inserted respectively; four string holes 24 into which two top-side transverse strings are inserted; and six string holes 24 into which three grip-side transverse strings are inserted. 48 string holes were longitudinal and transverse strings 21 and 22. The value of Ns/N was 0.71.
The other constructions were the same as those of the examples 1 and 2.
As shown in
The inclined string holes 23 formed at each of the left and right connection portions 17 were disposed at 5 o'clock and 7 o'clock, supposing that the ball-hitting face F is regarded as a clock face.
As shown in
The inclined string holes 23 formed at each of the left and right connection portions 17 were disposed at 5 o'clock and 7 o'clock directions, supposing that the ball-hitting face F is regarded as a clock surface.
Measurement of Coefficient of Restitution
As shown in
The above-described point A is a position spaced at 0 cm from the center of the ball-hitting face, namely, a position spaced at 0 cm from the longitudinal axis L1 of the racket frame and spaced at 18 cm from the top thereof. The above-described point B is a position spaced at 3 cm from the point A in the widthwise direction of the racket frame. The above-described point C is a position spaced at 6 cm from the point A in the widthwise direction of the racket frame.
As shown in table 1, the tennis rackets of the examples 1 through 4 in which the Ns/N was set to not less than 0.70 had higher coefficients of restitution than the tennis racket of the comparison example 1 at any of the hitting points A, B, and C. This is because the tennis rackets of the examples 1 through 4 had a larger number of strings having a large effective length than the tennis racket of the comparison example 1. Therefore in the tennis rackets of the examples 1 through 4, the region having a high restitution performance was not limited to the central portion of the ball-hitting face, but was widened. Particularly the extended longitudinal string holes greatly increase the effective length of the longitudinal strings tensionally fastened to the racket frame at the left and right sides of the ball-hitting face thereof. Therefore the tennis rackets of the examples 1 through 4 had outstandingly improved restitution performance at the left and right sides of the center of the ball-hitting face.
The restitution performance of the tennis racket of the example 3 and that of the tennis racket of the example 4 are compared with each other. The tennis racket of the example 3 had a little higher restitution performance than that of the example 4 at all of the points A through C, although the tennis racket of the example 4 had a larger number of strings having a large effective length than the tennis racket of the example 3. In the tennis racket of the example 3, the extended longitudinal string holes parallel with the longitudinal direction of the racket frame were formed at the connection portion. Thus the restitution performance at the points B and C widthwise spaced at the above-described interval from the center of the ball-hitting face can be more effectively enhanced than the tennis racket of the example 4 in which no extended longitudinal string holes were formed at the connection portion.
Number | Date | Country | Kind |
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2006-190971 | Jul 2006 | JP | national |