them were not provided. A number of impacts were simulated at different locations on the string-bed. The inbound velocity for the ball was 27.8 m-s'1 for all of the impacts. ACOR was found to decrease with increasing string tension and to be highest between the GSC and the throat, in agreement with other authors (Brody et al., 2002; Goodwill and Haake, 2001 & 2003). ACOR was also found to decrease as the impact position moved away from the GSC towards the side of the racket. The results were shown to be in agreement with experimental data. However, there was no explanation of the uncertainty in the experimental values or how they were obtained. The results showed that increasing the stiffness of the frame resulted in an increase in ACOR for the impacts at the throat and tip, while having no noticeable effect on those at the node (approx. GSC), in agreement with Goodwill and Haake (2003). The variation in ACOR with racket stiffness was more pronounced for impacts at the throat, which was also in agreement with Goodwill and Haake (2003). As with previous publications (Widing and Moeinzadeh, 1989; Widing and Moeinzadeh, 1990), the strings were assumed to be fixed at their intercepts, effectively ignoring the effect of string to string friction. Goodwill and Haake (2004b) measured horizontal string displacement of up to 12 mm for an oblique impact on a freely suspended tennis racket. Hence, Kanda et al.'s model is clearly not a realistic representation of reality and subsequent errors would become apparent if simulating an oblique impact. This investigation has shown that FE can be used to accurately simulate impacts between a tennis ball and racket. However, full details of any material properties and experimental validation should be included to enhance the value of the model.
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Ball spin plays an important role in the modern game of tennis. Previous work has shown that reducing the number of cross strings in a tennis racket can increase rebound ball spin. The aim of this study was to further our understanding of the effect of the number of cross strings on ball spin generation. Two rackets were tested, one with 16 main and 19 cross strings and the other with 16 main and 12 cross strings. The racket frame was fully-constrained and a ball was fired onto the strings at inbound angles of 24 and 38º. Inbound velocity was set at 30 m/s and inbound spin was varied from 0 to 500 rad/s. Ball velocity and spin, and lateral main string deflections during impact, were measured from high-speed video footage. Lateral string deflections were consistently larger for the racket with fewer cross strings. The racket with fewer cross strings produced slightly higher rebound spin and lower horizontal rebound velocity, which was attributed to the main strings returning during the restitution phase of the impact.
Measuring the properties of tennis rackets is an important step in evaluating racket design, selection and performance. Observing historical trends allows us to evaluate how materials and design have changed the racket, and hence the game , which could provide useful insights for product development, regulation and injury prevention strategies [12, 13], as well as spectator experience and education purposes . Allen et al.  measured a range of parameters, including I x′ and I z′ , in 100 rackets from different eras employing simple, low-cost and portable tools. They concluded that, since I x′ and I z′ were similar in magnitude, as detailed in Brody , measuring both is not always necessary when characterising a large number of rackets. In addition, they also presented that it is possible to estimate I x′ from models that use measurements of racket dimensions, mass and CoM location, which may be preferable in larger studies. Using a sample of ten, Brody  showed I y
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low (<200 fps) frame rates with a specific aim, whether this be analysis of player accuracy (Blievernicht 1968) or studying player biomechanics (Knudson and Blackwell 2005). There has also been some notable three-dimensional (3D) work focusing on the kinematics of the serve (Elliott 1986) and backhand (Elliott 1989). Sensor systems capable of recording multiple points using 3D coordinates in real time have also been used to track racket and upper limb movements. Mitchell et al. (2000) used a CODA (Cartesian optoelectronic dynamic anthropometer) system to compare the effect of racket inertial properties on serve speed. Ahmadi et al. (2010) used two inertial gyroscopes to measure upper arm rotation during the tennis serve. However, attaching sensors to the racket frame and/or upper arm adds mass, altering inertial properties possibly influencing player swing mechanics. Brody (2000) found that skilled tennis players were able to distinguish between rackets that differed by as little as 2.5% in swingweight (moment of inertia about the racket handle end).
Commercial devices, (e.g. the Babolat Racket Diagnostic Centre (RDC) (Babolat, France)), use a horizontal clamp arrangement to measure swingweight. Two springs, attached at a pivot four inches from the racket butt, create simple harmonic motion, from which the oscillation period can be measured. These machines use electronic timing to calculate swingweight.
Modern technologies, such as motion capture systems (both optical and marker- less), are more and more frequently used for athlete performance analysis due to their great precision. Optical systems based on the retro-reflective markers allow for tracking motion of multiple objects of various types. These systems compute human kinetic and kinematic parameters based on biomechanical models. Tracking additional objects like a tennis racket is also a very important aspect for analysing the player’s technique and precision. The motion data gathered by motion capture systems may be used for analysing various aspects that may not be recognised by the human eye or a video camera. This paper presents algorithms for analysis of a tennis racket motion during two of the most important tennis strokes: forehand and backhand. An optical Vicon system was used for obtaining the motion data which was the input for the algorithms. They indicate: the velocity of a tennis racket’s head and the racket’s handle based on the trajectories of attached markers as well as the racket’s orientation. The algorithms were implemented and tested on the data ob- tained from a professional trainer who participated in the research and performed a series of ten strikes, separately for: 1) forehand without a ball, 2) backhand without a ball, 3) forehand with a ball and 4) backhand with a ball. The computed parameters are gathered in tables and visualised in a graph.
Choppin found his model showed good agreement for rebound ball velocities close to the node of the racket and off-axis. The rigid-body racket assumption did reduce the agreement for impacts near the throat of the racket, however this was previously justified. Modelled outbound spin measurements were found to agree with experimental data at lower spin rates, but less so as spin rate increased above 2000 rpm. Choppin identified issue with this validation, including measurement error in his experimental data. He concluded that to investigate the causes of spin rate error in his model, the multi-variate regressions could be expanded to include spin rate as an additional parameter. The errors and uncertainty of his validation meant the model did not replace the existing ball-racket impact model in TennisGUT.
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Specification: Head Ti 4700 Tennis racket. A racket design tries to find an ideal balance of playing characteristics. When a tennis racket is designed, some compromises must be accepted: power vs. control, comfort vs. feel, light weight/maneuverability vs. solid shot response and stability [1, 19]. Design of the tennis racket was focused on many items, such as: racket size (dimensions– length, width, and thickness), size and shape of the racket head, size and shape of the racket handle, frame and string materials, weight, centre of mass and inertial characteristics, etc. The racket design is performed using PRO/ENGINEER software suite multiplatform, one of the most used integrated CAD/CAM/CAE systems. PRO/ENGINEER offers one of the world's leading parametric solid modeling packages. Tennis racket designed was thought to be composed of two main components: racket frame and strings. All parts go through the same stages of design. Design stages used commands. As the first result, a sketch of the racket frame was obtained, using the Extrude-Swept Blend-Curve- Sweep. Next were realized holes into the racket frame for string fixing. There were used Hole command for the first hole and Pattern command to multiply the created hole. Racket frame is ellipse section. The holes made in the racket frame have diameter of 2 mm, string diameter is 1.3 mm and they are arranged on the racket frame periphery at 19 mm distance vertically and 16 mm horizontally. Using the software facilities, the mass centre was determined . The figure 2 shows 3D model of the tennis racket.
The purpose of this study was to investigate the effect of String Vibration Damper on the myoelectric activity of the wrist extensors during the impact phase of backhand stroke technique.15 elite and 15 novice tennis players with an age ranging from18-25 years volunteered to participate in this study. Only one racket was used and was impacted by a pressurized ball. That was subjected to a constant velocity. The ball impacts were directed the racket throat area with and without using the String Vibration Damper. The participants were not allowed to see the ball impacts, as stand was placed between the participant and the racket. The experiment was repeated three times at the same day with rest periods in-between. The wrist extensors EMG data were collected with and without using the String Vibration Damper. Results revealed that there was no significant effec
The tennis racket design had many improvements in last few years. The racket heads have grown larger, on frames that have become lighter. The racket frame and strings are of great importance for the player performance. The paper proposes synthesis and mechanical testing of Nylon6,6/MWNT newer nanocomposite material to a tennis racket frame , the strings made by nylon fiber , the creating model of tennis racket frame and applying newer material and analysis. The nanocomposite using Universal testing machine, Impact and Hardness machine test the mechanical properties. The racket shape and dimensions can be established by the designer. The racket design was performed by using CREO software. The racket model can be implemented in Ansys analysis software in order to study the mechanical properties of the racket, especially the impact, vibration between tennis ball, string bed of the racket and transverse to frame.
corresponding to upright. Silhouette images of the racket model were rendered every 2°, which for typical racket head speeds during a serve [18, 45–48]; a high-speed camera would need to operate at 200 frames per second (fps), so that sufficient silhouette images could be obtained. The algorithm was instructed to perform two optimisations; the first worked backwards from when the racket was oriented at 0° to -40°, the second worked forwards from 0° to 30°. An orientation of 0° was used as a starting point, because it was found that this position provided a more accurate pose initialisation . Thus, for the first opti- misation, with the racket orientated at 0°, the candidate relative pose was obtained using the method described in Sect. 2.2. This scenario requires the operator to provide the algorithm with an initial approximate distance between the camera and the racket, i.e., 14 m should be sufficient for baseline shots (Fig. 3). The following optimisations were then initialised using the camera pose estimate from the previous solution. The 3D racket positions were obtained using the camera pose estimates to reconstruct the 130 coordinates on its face plane in the Y, Z, and resultant dimensions for each angle . Reconstruction results were validated against known 3D coordinates obtained from the racket model mesh.
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Modal analysis was used to determine the frequency of the first bending mode. The racket was suspended with string and a sensor (MetaWear CPro, Mbientlab Inc., San Francisco, CA, USA) was strapped to the handle (8 g sensor & strap). The string bed was ‘tapped’ with a ball to excite vibrations, with the accelerometer sampling at 800 Hz (BMI160 inertial measurement unit, Bosch Sensortec, Reutlingen, Germany). Data was logged in the sensor memory, transferred to an iPad via Bluetooth and downloaded (MetaWear App) to a laptop. The Fast Fourier Transform (FFT) function in Matlab R2106a (Mathworks) was applied to obtain the frequency. Tests were undertaken twice and the mean reported. The maximum difference between trials for a racket was 2 Hz (5 occurrences). Accuracy was assessed by fixing the sensor to a shaker and exciting frequencies of 100, 150 and 190 Hz, typical for tennis rackets  and predictions fell within 2 Hz.
The short duration (5 ms) of the impact between a tennis ball and string bed in a stroke [92–94] means that hand forces will have negligible effects on most stroke parameters. Pre-impact grip forces are associated (r 2 = 25 to 36 per cent) with post-impact peak forces and vibrations [95, 96], but are not related to ball rebound speed [97–100], and accuracy . A simulation study confirmed the lack of an effect of grip forces on the speed of ball rebound, but did predict potentially meaningful increases (up to 1 degree) in shot accuracy with high levels of grip axial torque . In summary, tennis players normally need only to grip the racket with enough pressure to control racket motion in the stroke. Given most ball rebound parameters, the racket essentially behaves mechanically at impact more like a freely moving rather than a restrained implement.
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PROTECTIVE EYEWEAR CERTIFICATION Protectors that have been tested to an appropriate standard by an independent testing laboratory are often certified and should afford reasonable protec- tion. The Protective Eyewear Certification Council has begun certifying protectors that comply with ASTM standard F803 (racket sports, basketball, base- ball, women’s lacrosse, and field hockey), ASTM standard F1776 (paintball), and ASTM standard F910 (youth baseball batters and base runners) stan- dards. 10 The Canadian Standards Association (CSA)
The paper takes table tennis robot stroking table tennis as research objects, it makes physical force analysis, and gets the physical force model existed drawbacks, to further optimize model, it proposes least square method motion trajectory model to recognize and predict table tennis motion trend. Finally by table tennis collision process, it deduces release speed, racket speed and others connections that plays positive roles in robot table tennis development.
physiological while the mental toughness and the level of parental support tests were used to investigate psychological and sociological attributes. A total of 537 ball sports, racket sports and target sports junior athletes, aged 13 years old were selected from the Malaysian Sports School and State Sports School to be involved in the field testing. A total of 85 participants was involved in the testing of the usability of the system and 374 junior athletes were tested to evaluate the accuracy of the system based on physical and physiological characteristics. Three sets of questionnaires were used to test the level of mental toughness, the level of parental support and the usability of STIDSS. Findings showed that for ideal anthropometrics characteristics, only male racket sports and female ball sports achieved superior standard. This study developed a new norm based on the total population of junior potential national athletes which covered both Malaysian sports school and nine state sports schools. Speed, agility, reaction time and cardiovascular endurance did not contribute directly to the performance of target sports but it significantly contributed to ball sports and racket sports. This study found that measurement of VO 2max uptake is not a priority
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Abstract—A racket-shaped slot ultra-wideband (UWB) antenna coupled with parasitic strips for band-notched application is proposed in this paper. By attaching a pair of parasitic rectangular strips on the bottom of the substrate, a band-notched characteristic is well realized. Adjusting the length, width of the two strips and the distance between them, a band-rejected filter characteristic at the WLAN operation in 5.15–5.825 GHz frequency band can be obtained. The fabricated antenna has a small size of 20 ×37.5 mm 2 . Good agreement is achieved
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The public transport sector generates significant financial resources that the different actors share. Indeed, this sector is regularly subject to violence between rival union auxiliaries. Their links with the official unions, allow them to enjoy the status of agents of taxation on behalf of the latter and to establish on the station space a form of racket that is practiced with violence. The currencies that are generated in the informal stations make them a coveted space. It remains difficult to estimate the totality of the sums of money accumulated by the different actors. But, we can get an idea of the sums collected in some places. These amounts range from 10,000 CFA to 100,000 CFA a day. They vary according to the density of traffic at the point of embarkation and disembarkation and the number of vehicles likely to load at this point. This collection provides substantial income for union auxiliaries as well as managers and chiefs.
Although the present study has yielded findings that establish positive links among TTT, executive functions, and visual perception, there remain some limitations. First, the results of the present study reflect the TTT effects during a 16-week training intervention. Continued improvement or maintenance of visual–perceptual and executive functions would strengthen support for TTT. Therefore, replication of this study with a long-term follow-up (eg, 6 months or 1 year after intervention) is warranted to discern the long- term impact of the TTT intervention. Second, follow-up studies are also needed to verify the functional outcomes of racket sports (ie, the correlation between improved visual– perceptual and executive functions and school functions). More effort should be made to help these children generalize the training effects to functional tasks that demand similar cognitive and perceptual functions. Third, individuals with BIF and MID are different in terms of their intellectual functioning or plasticity to any type of intervention. Future study should specify if all participants are individuals with BIF or MID. Last, the subjective outcomes (eg, perceived fatigue or satisfaction level) are important, and should have been reported for clinical aspects. Future study should adopt subject-outcome measurement and provide an adverse- effect report.
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