軟式網球線粗糙度對球拍特性影響-前導實驗

Influence of soft tennis string roughness on the racket performance-preliminary study

前言：本研究目的在於探討改變軟式網球線表面粗糙度對球線摩擦力、球撞擊球拍後震動響應、球速、轉數之影響。方法：實驗區分為材料及人體測試兩階段，第一階段先使用氧化鋁砂布No150#摩擦球拍甜區，以改變表面粗糙度，再利用白光干涉儀器測試球線表面粗糙度差異，並在球拍裝置Biopac三軸加速規後固定於夾鉗鋏器，球體由100公分處以自由落體落下於拍面甜區，以測得震動響應；第二階段為實際揮拍擊球，受試對象為台北體院軟式網球隊3名優秀選手，分別以未改變及以改變表面粗糙度之球拍，揮擊上旋球、平擊球及下旋球，利用Mega高速攝影機(1000Hz)分析球速及轉速。統計方法因樣本數量較少而採用敘述性統計。結果：未改變與已改變球線表面粗糙度之球線數值分別為3.12±0.37微米、6.81±2.50微米，震動響應減少14.59伏特，上旋球球速減少60%、平擊球減少33%、下旋球減少15%，上旋球轉數增加50%、平擊球增加34%，下旋球增加34%。結論：改變球線表面粗糙度後，會使球線表面粗糙度增加、震動響應減少、球速減低，球轉數增加等現象，因此軟網選手可利用此方法達到運動生物力學優勢。

Purpose: The aim of this study was to exam effects of surface roughness changes of soft tennis string on friction of string， vibration response， ball velocity and number of revolutions. Method: Material and hitting measurements were conducted， respectively. In first measurement， one emery cloth， No150#， was used to rub the sweet spot of the racket for changing its roughness. Friction of tennis string was measured by using a friction tester (ALGOL-HF-100). Vibration response of racket was measured by using a tri-axial accelerometer when the bounce response after a soft tennis ball， fall down from 100 cm height， hits against on the sweet spot of racket. In second measurement， 3 elite players hit top-spin， flat strike and back-spin by using the string with and without roughness changes. Mega high-speed camera at 1000Hz was collected batted ball for analyzing ball velocity and number of revolutions. Result: After surface roughness changes of soft tennis string， the friction of string increased about 0.02 kg， vibration response decreased about 14.59 v， ball velocity decreased (60% for topspin， 33% for flat strike and 15% for backspin)， and number of revolutions increased (50% for topspin， 34% for flat strike and 34% for backspin). Conclusion: Increased string roughness resulted in higher friction， lower vibration response， lower ball velocity and higher ball spin. Therefore， soft tennis player could get biomechanical benefit after adopting this method.