Kinematic Analysis of a Parallel Manipulator Driven by Perpendicular Linear Actuators

In this paper, a goniometer-type specimen stage with a linear actuation mechanism mounted on a rotation mechanism is introduced. The linear actuation mechanism was modeled as a spatial parallel manipulator consisting of a moving body, three linear actuators, and an anti-rotation mechanism. The three linear actuators were arranged perpendicular to each other. In the specimen stage, the linear actuators were in ball contact with the surface of a holder designed to hold a specimen. For the parallel manipulator, the ball contact was replaced with two prismatic joints and a spherical joint. The mobility of the manipulator without the anti-rotation mechanism was one degree of freedom greater than the number of actuators. Therefore, the redundant one degree-of-freedom motion was restrained using an anti-rotation mechanism with three rotation joints and two prismatic joints. The inverse and direct kinematics of the goniometer mechanism were derived and verified. In addition, the inverse Jacobian was derived, and local and global performance indices were analyzed by the terms of manipulability and isotropy. Finally, the goniometer-type specimen stage was designed by the global performance indices.

Exploring the Gaze Behavior of Tennis Players with Different Skill Levels When Receiving Serves through Eye Movement Information

Background: The purpose of this study was to explore the gaze behavior of tennis players with different skill levels when receiving serves through eye movement information. Methods: The skill level was divided into group A (experts, with more than 10 years of playing experience) and group B (novices, with less than 2 years of playing experience). We compared the differences in gaze behavior between groups A and B at the head-shoulder, trunk-hips, arm-hand, leg-foot, racket, ball, and racket-ball contact area seven positions using the Eye-gaze Response Interface Computer Aid (ERICA) device. Data were analyzed using two-way ANOVA. Results: Compared with the novices, the experts have more gaze time in the head–shoulders, rack, and ball when serving forehand (p < 0.01). The experts also have more gaze time on the head–shoulders, trunk–hips, racket, ball, and racket–ball contact area when serving backhand (p < 0.05). Conclusions: Expert athletes have a longer stare time for a specific position, which mainly determines the direction of the ball. Tennis coaches can increase the gaze time for these four positions and improve tennis players’ ability to predict the direction of the ball.

Effects of carriage flexibility on friction force in linear ball guides

This paper presents the effects of carriage flexibility on the friction force in linear ball guides, which includes hydrodynamic rolling friction, elastic hysteresis friction, slip friction, and drag friction. To this end, we developed a computational model for the friction force in linear ball guides that accounts for the carriage flexibility. The model was validated through experiments, and the results prove that it provides more accurate friction-force estimates than the conventional model under the assumption of a rigid carriage. Subsequently, we examined the effects of external load, preload, and speed on the friction force. Among several friction components, hydrodynamic rolling friction makes a major contribution to the total friction force. Ball contact loads, which significantly vary with carriage flexibility, were found to influence the hydrodynamic rolling, elastic hysteresis, and slip friction forces. The proposed model considering carriage flexibility in linear ball guides is expected to find use in the design and operation of linear-ball-guide systems.

Biomechanical analysis of accuracy penalties-kicking performance for Turkish Soccer players: Group-based analysis without goalkeeper

Background and Study Aim. It is stated that kinetic performance factors are important in the successful execution of accurate kick-penalties, thus, its offer excellent performance despite a substantial kinetic method change in their implementation. The aim of the study is to biomechanical analysis of accuracy penalties-kicking performance for Turkish soccer players. Material and Methods. The study group consisted 15 male students of Turkish Regional Amateur League players (Age: 21.08± 1.56 years old). Two video cameras placed at optical axes X&Y filmed penalty-kick performance of the subjects. we analysed the best three scores by video analysis Dartfish 9.0 software. Standard statistical methods were used for the calculation of mean±SD. the Statistical significance at p<.05 for Pearson product—moment correlations. Results. Accurate penalty-kicks showed significant positive relationship of knee Pi angle value in backswing, ball Contact phases, trunk angle value in ball contact with the accuracy at p<.01. Significant negative relationship of inclination_body angle value, time of foot contact at p<.01, and distance pivot foot&ball value at p<.05 in the follow-through phase. Conclusion. Such knowledge should aid in clarify the relationships between variables of penalty kicking during The performance phases and accuracy. the present preliminary investigation of accurate penalty-kicks performance indicates Support-leg characteristics demonstrated in knee angle values an important factor in Backswing, Ball Contact phases with the accuracy of penalty kicking. also, the Foot Contact time and Inclination_Body angle in that.

Mechanism of the Breakage of Spherical Gypsum Particles under 3-Point Contact Conditions

Particle breakage has a great influence on the mechanical properties of coarse-grained soil materials. In the structure, a particle usually contacts with several surrounding particles when breakage occurs. The crushing mechanism of spherical particles under three-point contact conditions was investigated theoretically and experimentally. In the theoretical analysis, the contact force required for particle breakage is solved by using a stress superposition method based on the ball–ball contact model. To verify the theory, particle contact tests of gypsum spheres under three-point contact conditions were carried out. The experimental results are consistent with the theoretical prediction. Different from the ball–ball contact test, the rupture surface after breakage is a fixed plane passing through all three contact points under three-point contact conditions. Under multi-point contact conditions, the size of the conical core depends on the normal force on the contact point at the moment of particle breakage. Multi-point contact makes particle breakage more difficult, and the stronger the constraint of surrounding spheres, the more difficult it is for the particle to break. Both the theory and the experiment provide evidence that the arrangement of particles affects the overall strength of the coarse-grained soil structure.

NON-HEADER IMPACT EXPOSURE AND KINEMATICS OF MALE YOUTH SOCCER PLAYERS

Previous studies have investigated the head impact kinematics of purposeful heading in youth soccer; however, less than a third of all head injuries in youth soccer have been found to involve ball contact. The aim of the current study was to identify the head impact kinematics and exposure not associated with purposeful heading of the ball in male youth soccer. Headband-mounted sensors were used to monitor the head kinematics of male junior varsity and middle school teams during games. Video analysis of sensor-recorded events was used to code impact mechanism, surface and site. Junior varsity players had non-header impact rates of 0.28 per athlete-exposure (AE) and 0.37 per player-hour (PH), whereas middle school players had relatively lower non-header impact rates of 0.16 per AE and 0.25 per PH. Such impact rates fell within the large range of values reported by previous studies, which is likely affected by sensor type and recording trigger threshold. The most common non-header impact mechanism in junior varsity soccer was player contact, whereas ball-to-head was the most common non-header impact mechanism in middle school soccer. Non-header impacts for junior varsity players had median peak kinematics of 31.0 g and 17.4 rad/s. Non-header impacts for middle school players had median peak kinematics of 40.6 g and 16.2 rad/s. For non-header impacts, ball impacts to the rear of the head the highest peak kinematics recorded by the sensor. Such data provide targets for future efforts in injury prevention, such as officiating efforts to control player-to-player contact.

Numerical Characterization of the Load Distribution in Ball Screws

Load distribution in ball screws is a representation of the ball contact stress, and it is fundamental to understanding the behavior of these machine elements. This work aims to conduct a multi-variable analysis of the load distribution in ball screws. For this purpose, a numerical tool is developed for the generation and calculation of ball screw FEM models, which has been validated against the state of the art. Many different design variables are studied in order to obtain a general characterization of the morphology of the load distribution in ball screws. The two most characteristic features, the non-uniformity at a local and global level are identified, along with as the possible causes of their appearance and the consequences that they may cause.

Predicting golf ball launch characteristics using iron clubhead presentation variables and the influence of mishits

In golf, it is well understood that the interaction between the clubhead and ball determines the initial ball launch conditions. Specific knowledge regarding these relationships for iron clubs, particularly when clubhead and turf interactions are considered, would be both novel and of benefit to practitioners. Linear regression analysis was used to determine relationships between selected clubhead presentation and shot outcome variables for a sample of 1127 ‘5-iron’ shots hit from natural turf by 96 golfers. As expected, clubhead speed was the most significant predictor of ball speed, with obliquity of impact and eccentricity of the impact location making smaller, yet statistically significant contributions. Marginally ‘fat’ strikes, whereby the leading edge of the clubhead was only slightly beneath the ground at impact, appeared to have a lesser effect than expected in terms of ball speed. Effective loft was found to be the strongest predictor of vertical launch angle, whilst clubhead speed and spin loft had the greatest influence in the model for predicting total spin; inclusion of ‘thin’ strikes (i.e. those struck with the leading edge) appeared to create a non-linear element to these models and consequently overestimated the influence of vertical impact location in both cases. These findings suggest that determination of impact location, particularly for instances whereby ball contact is not wholly on the club face, is critical in research concerning irons. Overall, this study makes an original contribution to the understanding of 5-iron shot outcomes based on clubhead presentation characteristics.

Upaya Meningkatkan Hasil Belajar Passing dalam Permainan Sepak Bola melalui Model Pembelajaran Kooperatif Tipe TGT (Teams Games Tournament) Siswa SMP Negeri 1 Tanasitolo Kabupaten Wajo

This research is a classroom action research conducted in 4 meetings in cycle I and cycle II, and is designed through four stages, namely planning, implementing, observing, reflecting. The data source of this research is the students of class VIII SMP Negeri 1 Tanasitolo, Wajo Regency, totaling 27 people. The collection of data on the ability of passing by using the prefix technique assessment sheet, body position, foot-to-ball contact, and final stance. The results of the quantitative analysis of the results of learning passing data in the game of soccer show that the number of students who completed the first cycle was 16 with a percentage of 59.25% and the number of students who completed the second cycle was 27 with a percentage of 100%. Based on the results of this study, it can be concluded that physical education learning through the TGT (Teams Games Tournament) type cooperative learning model can improve the results of learning passing in soccer games for students of SMP Negeri 1 Tanasitolo, Wajo Regency.Keywords: Football, passing, learning outcomes, learning model, TGTAbstrakPenelitian ini merupakan penilitian tindakan kelas yang dilaksanakan sebanyak 4 kali pertemuan pada siklus I dan siklus II, dan dirancang melalui empat tahapan yaitu perencanaan, pelaksanaan, observasi, refleksi. Sumber data penelitian ini adalah siswa kelas VIII A SMP Negeri 1 Tanasitolo Kabupaten Wajo yang berjumlah 27 orang. Pengumpulan data kemampuan passing dengan menggunakan lembar penilaian teknik awalan, posisi badan, perkenaan kaki dengan bola, dan sikap akhir. Hasil analisis kuantitatif data hasil belajar passing dalam permainan sepak bola menunjukkan bahwa jumlah siswa yang tuntas pada siklus I adalah 16 orang dengan persentase 59,25% dan jumlah siswa yang tuntas pada siklus II adalah 27 orang dengan persentase 100%. Berdasarkan hasil penelitian ini, dapat disimpulkan bahwa pembelajaran pendidikan jasmani melalui model pembelajaran kooperatif tipe TGT (Teams Games Tournament) dapat meningkatkan hasil belajar passing dalam permainan sepak bola siswa SMP Negeri 1 Tanasitolo Kabupaten Wajo.Kata kunci: Sepak bola, passing, hasil belajar, model pembelajaran, TGT

KINEMATICAL CHARACTERISTICS OF ACCURATE PENALTY-KICKING FOR TURKISH FOOTBALL PLAYERS IN GOALKEEPER CONFRONTATION

This study aimed to analyze the kinematical characteristics values of accurate penalty-kicking for Turkish football players in goalkeeper confrontation. Fifteen male Turkish Regional Amateur League players (Age: 21.08± 1.56 years old) was scanned, by two video cameras synchronous in two-dimensional (2D), placed at optical axes X&Y. the best three tries of penalty kicking performance were analyzed by video analysis Dartfish 9.0 software. Standard statistical methods were used for the calculation of mean±sd, Pearson test for the correlations between all variables. A value of p-value ≤ 0.05 was considered a threshold of statistical significance. The results were shown in the ball contact phase that the distance pivot foot & ball factor has a statistically significant effect in producing accuracy (p-value=.001), and the interaction between two main factors namely the trunk and inclination body angles has a statistically significant effect with a p-value≤.05 in producing accuracy too. In addition, in the followthrough phase, we can see too the statistically significant effect in p-value≤.005 of the trunk angle, and in pvalue≤.05 of the thighs angle in producing accuracy. As a conclusion, it can be conveyed that the distance between the support leg and the ball is very decisive for the kinematic profile formed such as contraction of the abdominal muscles (trunk angle), the amortization process (the pivot leg angle), shot power (angle and length of the shot leg swing trajectory), where these aspects are significantly affected to the shot power, ball velocity and the level of accuracy.