著者

川副 嘉彦 武田 幸弘 中川 慎理

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集C編 (ISSN:18848354)

巻号頁・発行日

vol.79, no.799, pp.726-737, 2013 (Released:2013-03-25)

参考文献数

14

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Several former top players sent a letter to the International Tennis Federation (ITF) encouraging the governing body to revisit the question of rackets. In the letter, the players wrote that racket technology has led to major changes in how the game is played at the top level. This paper investigated the physical properties of a new type of racket with active piezoelectric fibers appeared recently in the market, and predicted the various factors associated with the frontal impact, such as impact force, contact time, deformation of ball and strings, and also estimated the racket performance such as the coefficient of restitution, the rebound power coefficient, the post-impact ball velocity and the sweet areas relevant to the power in tennis. It is based on the experimental identification of the dynamics of the ball-racket-arm system and the approximate nonlinear impact analysis with a simple swing model. The predicted results with forehand stroke model can explain the difference in mechanism of performance between the new type racket with active piezoelectric fibers and the conventional passive representative rackets. It showed that this new type racket provides higher coefficient of restitution on the whole area of string face and also gives larger rebound power coefficients particularly at the topside and bigger powers on the whole area of string face but the difference was not so large. It seems that the racket-related improvements in play are relatively small and the players themselves continue to improve, accordingly there is a gap between a perception and reality.

著者

川副 嘉彦 中川 慎理

出版者

一般社団法人 日本機械学会

雑誌

シンポジウム: スポーツ・アンド・ヒューマン・ダイナミクス講演論文集

巻号頁・発行日

vol.2010, pp.147-152, 2010

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The previous paper of the authors made clear the mechanism of top-spin performance in tennis and its improvement by lubrication of strings according to the high speed video analysis. As the main strings stretch and slide side ways more, the ball is given more spin due to restoring force parallel to the string face when the main strings spring back and the ball is released from the strings. Since the notches of strings decrease spin rate, the lubricant materials are effective to the notched strings and the spin rate of newly strung tennis racket without notches is much larger than that of used racket with notches. Furthermore, it showed that the more spin results in the reduction of shock vibrations of the wrist joint during impact. There are several strings now on the market that are designed explicitly to take advantage of the slippery string mechanism for top spin improvement. This paper showed the spin behavior of the ball and the revolutionary flat strings during oblique impact in the laboratory by the high speed video analysis and recognized that flat strings are more slippery and generate more spin than the conventional strings.

著者

川副 嘉彦 武田 幸弘 中川 慎理 Federico CASOLO 友末 亮三 吉成 啓子

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集C編 (ISSN:18848354)

巻号頁・発行日

vol.79, no.808, pp.4994-5009, 2013 (Released:2013-12-25)

参考文献数

13

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The lightweight racket with handle-light configuration and large head size is recent tendency of high-tech tennis rackets, increasing power or post-impact ball velocity with an increasing racket swing speed. This paper investigated the performance of lightweight balanced racket with super-large head size with 120 square inches in terms of feel or comfort. It predicted the effect of the mass and mass distribution of super-large head sized rackets on the impact shock vibrations of the racket handle and the player's wrist joint when a player hits a flat forehand drive. The prediction is based on the identification of the racket characteristics, the damping of the racket-arm system, equivalent mass of the player's arm system and the approximate nonlinear impact analysis in tennis. A lightweight balanced racket (mass: 292 g, the center of gravity LG: 363 mm from the butt end) and a conventional weight and weight balanced racket (349 g, LG: 323 mm) are selected as representatives. These two super-large head sized rackets made of carbon graphite have the same head size and same geometry. The result showed that the shock vibration of the lightweight balanced racket with super-large sized head is much larger than that of the conventional weight balanced type racket. It also showed that the sweet area of the former in terms of the shock vibration shifts from the center to the topside on the racket face compared to the latter. This is because the location of the grip on the racket handle is further from the location of the node on the handle of the first mode of lightweight balanced racket than that of the conventional weight balanced racket.

著者

川副 嘉彦 武田 幸宏 中川 慎理

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 C編 (ISSN:03875024)

巻号頁・発行日

vol.76, no.770, pp.2646-2655, 2010-10-25 (Released:2017-06-09)

参考文献数

18

被引用文献数

1 1

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There has been no question that some strings do provide a better grip than others, but that did not guarantee that the ball will produce more spin. Furthermore, experiments with hand-held rackets has been needed to solve the vexed question of how players can tell the difference between different strings when laboratory tests indicate that they should play the same. The previous paper of the authors made clear the mechanism of top spin performance in actual tennis and its improvement by lubrication of notched nylon strings according to the high speed video analysis on the court for the first time. It succeeded in an experiment showing that as the main strings stretch and slide side ways more, the ball is given more spin due to restoring force parallel to the string face when the main strings spring back and the ball is released from the strings. Since the notches of strings decrease spin rate, the lubricant materials are effective to the notched strings. Furthermore, it showed that the more spin results in the reduction of shock vibrations of the wrist joint during impact. This paper showed that the ball is given less spin rate (40% decrease) with the notched used strings compared to that with the new strings in the case of the nylon in this experiment, which has remained to be seen which gives more spin between new strings and the lubricated used strings, and it showed that the ball is given more extra spin (30% increase) by oil lubrication at the string intersections compared to that with the notched used nylon strings. Furthermore, it also showed that the used natural gut with notches decrease 70% of spin rate compared to the new natural gut without notches in the another experiment, which has remained to be seen whether the same results will be obtained. It also showed the difference of the topspin behavior when a pro and an amateur hits a ball.