PUTTING BIOMECHANICAL INFORMATION INTO PRACTICAL USE

In this keynote lecture, activities of the biomechanics research project of The Japan Association of Athletic Federations are first introduced with examples of speed and motion analyses of elite sprinters in world level competitions. The speaker explain various feedback processes of biomechanical information to athletes and coaches, and propose a procedure to bridge the gap between theory and practice. For effective use of biomechanical data in practice, we have to install two kinds of analysis abilities : a qualitative and quantitative analysis abilities. Without one of two abilities we will be unable to be a good sport biomechanist. A sensible quantitative analysis is derived from a sensitive qualitative analysis and the latter is improved by the former

Frequency Response of Servomechanisms with Non-linear Friction

In this paper, the effect of non-linear friction, i.e. static and coulomb friction, on frequency response of the servomechanism, is considered in order to get the knowledge for synthesis of the servomechanism. The effect of non-linear friction does not depend on the absolute value of friction torque, but on the ratio of the static friction torque to the amplitude of sinusoidal input torque F/A. If the amplitude of sinusoidal input torque is not so large as the static friction torque, the output speed of the servomechanism has a dead zone in the low frequency range, and whether the output speed has a dead zone or not depends on the frequency of the sinusoidal input torque, the ratio F/A, and the other system parameters. The limiting condition of the output speed with a dead zone is considered. When the input torque varies sinusoidally, the waveforms of output speed of the servomechanism in which the non-linear friction characteristic is contained, are strictly analysed. From the results of the above analyses, the effect of non-linear friction on the frequency response of the servomechanism is discussed through the method of comparing the first harmonic component of the output speed with input torque. The magnitude of gain is less than that of the linear first order system and converges to a certain value determined by the characteristic of the non-linear friction in the low frequency range. The shape of gain curves is like the linear first order system and the curves approach the -20dB/decade line in the high frequency range. The break point frequency becomes a little larger than that of the linear first order system as F/A becomes larger. On the other hand, the phase angle delays more than that of the linear first order system in the low frequency range and less than that in the high frequency range. Moreover, the phase characteristic curves converge to a certain angle larger than -90°. So, in the high frequency range, the non-linear friction acts so as to stabilize the performance of the whole system

A BIOMECHANICAL METHOD FOR THE EVALUATION OF SPORTS TECHNIQUES BY STANDARD MOTION, MOTION VARIABILITY AND MOTION DEVIATION

ABSTRACT The essential but most difficult steps in an optimization loop of sports techniques are the evaluation and diagnosis of the techniques of students and/or athletes, and the identification of their technical faults and limiting factors. This process is frequently referred to as technique analysis in sport biomechanics but the concept of technical analysis is less well developed. Teachers and coaches frequently adopt a model technique or a template of model performance approach in which sequential pictures and figures of an outstanding athlete or skilled performer are used as a motion pattern model. This paper proposes a biomechanical method for the evaluation of sports techniques in which an averaged motion pattern of skilled performers is used as a standard motion, and motion variability and motion deviation are employed as indices to identify critical technical points and faults of an athlete

THE NEXT STEPS FOR EXPANDING AND DEEPENING SPORT BIOMECHANICS

Starting with introduction of the activities of biomechanics research projects of JAAF in which I was involved, how we conducted feedback of sport biomechanics data to athletes and coaches will be described. I will share ideas to find solutions to some long-standing questions in sport biomechanics and in the field, and to further expand and deepen sport biomechanics. Topics are learning from skilled athletes, exchanging basic and practical biomechanics, i.e. sport biomechanics，expanding sport biomechanics to practice in the field

Self-excited Oscillation of Relay Servomechanism with Coulomb Friction and its Graphic Solution

In this paper, the authors treat the relay servomechanism containing Coulomb friction as one of the control systems with multiple nonlinearities, and are particularly concerned with the self-excited oscillation of this relay servomechanism, discussing the effect of the Coulomb friction on its performance. In the case where the relay has hysteresis but no dead zone in its characteristics, the self-excited oscillation occurs in the servomechanism and the waveform and the frequency of the oscillation are greatly affected by the Coulomb friction. The output waveform and the freqency in this state are analyzed exactly, using the fact that the Coulomb friction characteristic in a periodic state can be treated as the ideal relay characteristic, and the effects of the Coulomb friction on them are considered. Moreover, the authors develop the graphic method of solving the self-excited oscillation of the relay servomechanism. Using this approximation method, the frequency of the self-excited oscillation can be obtained graphically through the vector locus of the transfer function of the linear part of this servomechanism plotted on a complex plane. The result obtained by this approximation method shows a good agreement with the theoretical one

ANALYSIS OF RELATIONSHIP BETWEEN HAMMER HEAD VELOCITY AND RADIUS OF CURVATURE

INTRODUCTION: In many research papers, the relationship between the hammer head velocity and the radius of curvature of hammer was discussed. The purpose of this study was to re-examine the relationship between the hammer head velocity and change in the radius of curvature with the 2-D computer simulation

COMPARISON OF KINETICS OF THE LEG JOINTS IN SEOI-NAGE BETWEEN ELITE AND COLLEGE JUDO ATHLETES

The purpose of the present study was to identify biomechanical factors that could be used for the evaluation of seoi-nage technique by comparing the techniques of elite and college-level judo athletes. The motion data of the seoi-nage were collected on three male elite judo athletes and nine male student judo athletes using a three-dimensional motion analysis technique and qualitatively compared. This study found that the peaks of the knee flexion torque, knee negative power, hip extension torque and hip positive/negative power on the swing leg of elite athletes was much greater than those of the college athletes. These indicated that the knee and hip joint contributed to the mechanical energy absorption of the tori’s body in the early phase and generated the positive power in the throwing phase

Propagation of Electrostatic Waves near the Lower Hybrid Frequency in a Toroidal Plasma, NOVA-I

Resonance cones in a lower hybrid range of frequency are observed and confirmed under the combined influence of toroidicity and inhomogenity in a toroidal device NOVA-I. The resonance cone is investigated in two different plasma sources, i.e. (A) a steady plasma of low density (Nₑ, ～5×10⁹ cm⁻³), and (B) a pulsed tokamak plasma of high density (Nₑ～2×10¹³ cm⁻³). In case (A), the experimental results agree well with the trajectories computed from a simple cold plasma dispersion relation. Even in the high density tokamak plasma of case (B), a wave penetration toward the plasma center is observed and its behavior also agrees qualitatively with the thoery

Heat Transfer by Natural Convection in Laminar Boundary Layer on Vertical Flat Wall

In this paper, we have studied theoretically the heat transfer by laminar natural convection from a bot vertical flat wall to the surrounding fluid. This problem has already been theoretically studied by Pohlhausen, but his method is very troublesome and since he uses Schmidt and Beckmann's experimental results for air, Pohlhausen's solution is not applicable to other kinds of fluids except air. We have analysed this problem for gas and liquid by means of three different approximate methods, and compared each result with the other