The purpose of this study was to formulate the dynamic contribution of estimated muscle force in consideration of muscle contraction mode. The upper body with a racket was modeled as a linked eleven-segment system. The analytical form of the equation for the system was obtained from the combination of 1) equations of motion for individual segments, 2) equations for constraint condition in which adjacent segments are connected by individual joint, and 3) geometric equations for anatomical constraint axes of wrist and elbow joints. Motion dependent term, which shows large contribution in generation of racket head speed, is converted into other terms by using a recurrent equation with respect to the generalized velocity vector in discrete time system. Individual muscle torques, which are generated by the muscle forces, are estimated by using a musculoskeletal modeling software (SIMM; MusculoGraphics Inc.). With the estimated muscle torques, the formula for muscle torque contribution to the generation of generalized velocity vector of the system in consideration of muscle contraction mode is derived.

View full abstract

It is important that we know the most suitable exercise command in sports for results improvement. The acquisition of the most suitable exercise command is effective using a musculoskeletal model to have different characteristic parameters such as height and the weight of the player by forward dynamics simulation. We built musculoskeletal model for exercise skill optimization in this study using Open Dynamics Engine of the dynamics operation library. Because ODE can make any shapes easily and treat it dynamically, the simultaneous optimization of human movement and parameter implement are enabled. The model to suggest was comprised of a head, the body, humerus, radius, ulna, a hand, pelvis, thighbone, lower leg bone, foot and toe. These models were connected by ball and socket joint of 3 degree of freedom and hinge joint of 1 degree of freedom with human articular range of motion which were API of ODE. The placement of the muscle of the power source is decided based on the data that an initial point and terminal are shown in BodyParts3D and the muscular strength is decided using a muscle model thought about by Hill-Stroeve.

View full abstract

The purpose of this study is to develop a new method for designing compression sportswear from the viewpoint of force by simulation. Applied simulation techniques are 1) skin strain simulation, 2) fabric strain simulation using the anisotropic hyperelastic model, and 3) musculoskeletal simulation. For skin strain simulations, a three dimensional computer graphic (3D-CG) polygon strain was calculated as a skin strain using a 3D-CG model that simulates the human body (CG-Human-Model). The initial strain and the strain caused by physical exercise were given to the polygon model representing the shape of the sportswear (CG-Sportswear-Model). The strain of the CG-Human-Model was given to the CG-Sportswear-Model. In-plane and out-of-plane forces resulting from the CG-Sportswear-Model are calculated using anisotropic hyperelastic models. These forces were given to the musculoskeletal simulation as the external forces, and muscle activity required for any given physical exercise (e.g. swimming motion) was calculated. Information of forces and muscle activity are very useful in designing compression sportswear. It is believed that this new method for designing compression sportswear based on simulation is a sophisticated technique because this method takes into account not only forces resulting from sportswear but also the effect of these forces on physical exercise.

View full abstract

The objective of this study was to develop the method of musculoskeletal simulation for a swimmer attaching a competitive swimwear. For the simulation, the body geometry and joint motion were put into the swimming human simulation model SWUM in order to calculate the distributed fluid forces acting on the whole swimmer's body. The distributed fluid forces were put into the musculoskeletal model. In addition to the fluid forces, the forces induced by the tension of the swimwear were also considered. The distribution of the forces acting on the swimmer was calculated from the stress distribution of the swimwear. Since the swimwear targeted in the present study was a half spat type, the forces by the swimwear acted on three segments; the right and left thighs, and the pelvis. Therefore, the ratio of one distributed force to these three segments had to be determined. In order to determine this ratio, the deformation of the swimwear measured in an experiment was used. As an example, the simulation for the crawl stroke was conducted. The results showed the time-varying effect of the swimwear on the muscle activity during swimming.

View full abstract

We developed the method to measure the three-dimensional posture of the golf club head based on one photo taken by one set of a camera, and found the following in terms of the measurement accuracy. (1)The measurement error can be decreased by putting markers on the wider surface of a head. (2)In the case where the posture of a head significantly deviates from the standard posture, the measurement accuracy deteriorates compared with the case of a small deviation. (3)The measurement error can be reduced by identifying the coordinates of the center of markers instead of visually selecting a pixel as the center of markers.

View full abstract

As topspin has been becoming a vital component for modern-day tennis, precise researches of friction between the string-bed and ball were carried out. However, from another viewpoint, it is necessary to clarify the relation between the grip angle and topspin in order to acquire the technique quickly or to prevent the wrist injury that occurs by taking a swing of topspin. The aim of this research is to make the measuring system that acquires the angle of wrist joint during the racket swing of topspin. In order to measure hand and forearm posture in inertial frame of reference during racket swing, two inertial sensors were attached to the back of hand and forearm. The angular velocity and acceleration were acquired from these sensors, and from the data, Euler angles were calculated in three-dimensions. From these Euler angles, the wrist angle was computed, and the difference of wrist angle during the swing between the Western grip and the Eastern grip was compared. These results showed that this measuring method expressed the characteristic of topspin precisely.

View full abstract

The purpose of this study was to verify the accuracy of 3D inertial sensor, based on the motion capture system, and analyze 3D motion of human body and putter club during golf putting. To test the accuracy of 3D inertial sensor, we used the physics pendulum of firmly fixed putter club. Ten putts were tried using the physics pendulum as accurately as possible, in order to reach a target distance of 0.5, 1.0, 1.5, 2.0, 2.5m. Then three experienced male golfers participated in this study. They executed putts of the same distance. 3D angular velocity of the putter club during golf putting performed by physics pendulum and human was calculated from 3D inertial sensor and motion capture system (MAC 3D). When participants performed putts, 3D angular velocity of the trunk was also calculated from inertial sensor and motion capture system. The results showed that difference between angular velocity calculated from inertial sensor and the same parameters calculated from motion capture system were relatively large. However, the 3D inertial sensor used in this study basically performed well because it captured motion trend of the putter club and the trunk. Additionally, we found that the more coefficient of variance of the angular velocity calculated from inertial sensor at impact increase, the more putting success rate decrease. These results of this study suggested that we can estimate putting skill by computing coefficient of variance of the angular velocity calculated from inertial sensor at impact.

View full abstract

This paper proposes the calibration method of magnetic field sensor using inertial sensor. The calibration of magnetic field sensor is effectiveness as the compensation method of static magnetic disturbance. In the prevous studies, the calibration methods using the special devices have been proposed. On the other hand, the magnetic field sensor is attached to the body segment in body motion measurement. It is necessary to develop the calibration method for body motion measurement. In this study, we developed the calibration method of magnetic field sensor for body motion measurement. This method can estimate the calibaration parameter of magnetic field sensor by applying the inertial sensor output to Extended Kalman filter. Futhermore, This method was extended to the method considering the alignment error between the inertial and magnetic field sensors.

View full abstract

The purpose of this study was to investigate the effects of closed basket weave ankle taping on the vertical ground reaction force and ankle movement during the contact phase before the take-off in vertical jump performance. Twelve healthy young men performed a vertical jump performance on a force plate without (CON) or with ankle taping (closed basket weave technique: CBW) of the right ankle joint. Vertical jump ability was assessed using two styles of vertical jump with no arm swing: a countermovement jump (CMJ) and squat jump (SJ). From the vertical ground reaction force (GRF), maximum jump height (Ht), vertical impulse (VI), rate of force development (RFD), maximum GRF (GRFmax) during the contact phase before the take-off in jump performance were determined. Also, movement analysis, range of motion (Δ ank) and angular velocity (Vank) of ankle joint were caliculated . Ht and RFD, Δ ank, Vank were significantly lower for CBW than CON in CMJ, but not in SJ. Conversely, VI and GRFmax were not significantly different between the groups in either jump condition. These results suggest that ankle taping impairs countermovement jump performance, due to a decreased ability to rapidly develop large force and plantar-flexion motion on the ground before the take-off.

View full abstract

Recently mobile devices are in widespread use. However, there is fear that flexing neck joint while operating mobile devices affects standing posture and body balance in an adverse way. Then the purpose of this study was to clarify the influence of operating mobile devices on body balance during standing. Nine male and a female performed standing on the force platform for three minutes at 6 conditions as follows: 1) with eyes open, 2) with eyes closed, 3) while flexing neck joint with eyes open, 4) while flexing neck joint with eyes closed, 5) while flexing neck joint and holding mobile devices with eyes open, and 6) while operating mobile devices. The center of pressure: COP trajectory was measured using the force platform during standing, and area of a circle of root mean square for COP trajectory was calculated. As compared to among conditions for COP trajectory, it was finding that operating mobile devices didn't impair body balance during standing.

View full abstract

The purpose of this study was to propose a methodology which realizes residual error reduction of whole-body CG's acceleration by modifying body specific parameters (e.g. mass, moment of inertia, and position of CG at each segment) for a dynamic contribution analysis of human movements. Since the dynamic contribution analysis, which decomposes generalized acceleration vector of target system into joint torque, gravity, and motion dependent terms, is based on the equation of whole-body motion, a type of analytical formula of the equation of motion was derived by the combination of 1) equations of motion for individual segments and 2) geometric constraint equations of segments connecting to its adjacent segments with the joints. In order to obtain the relationships between the inertia parameters and the whole-body CG's accelerations, a sensitive matrix relating inertia parameter vector to the whole-body CG's acceleration vector was calculated by adding 1% perturbation in nominal value of each inertia parameter. And then by using the sensitive matrix and the error acceleration vector at each time, an error equation with respect to the inertia parameters was derived in matrix form expression. A renewal parameter vector was calculated by the method of least square from the error equation with use of a constraint condition and a step size coefficient in order to deal with the significant nonlinearity of the system. A linked multi-segment simple simulation model, 4-link rigid segment model connecting to the ground via a virtual joint, was used to clarify the efficiency of the proposed method. From the results obtained in the simulation, the proposed method enables us to reduce residual errors of CG acceleration in the dynamic contribution analysis for a whole-body system.

View full abstract

Foot muscles are divided into two muscle groups: plantar intrinsic foot muscles (PIFM) and the extrinsic foot muscles (EFM); however, it is still unclear how PIFM and EFM separately contribute to the force generating capacity of the foot. Muscle force produced by isometric contractions is specific to the muscle length. From the length-tension relations of EFM, the contribution of EFM to the force generating capacity of the foot might be able to estimate to some extent. The purpose of the study was to investigate the relationships between ankle-knee joint angle and maximum isometric force of the toe flextion in the sitting position. We found that there was the optimum joint angle for the maximum isometric force of the toe flexion in the sitting position.

View full abstract

In this research, we fabricated triaxial force sensors which can measure tongue activities. In order to analyze the role of tongue activity of front part (anterior tongue) and back part (posterior) of the tongue, we fixed two triaxial force sensors to the palate. Our triaxial force sensors also have temperature sensors, which can measure the temperature change in the mouth so that temperature drift of the force sensors output can be compensated. In the liquid-swallowing experiment, pressure and shear force distributions were observed to clarify tongue motion. We measured and calculated anterior and posterior tongue activities during swallowing, and found that anterior tongue activity was larger than posterior tongue activity. These results indicated that the anterior tongue works as an anchor and the posterior tongue works as an actuator which transports the food or liquid to the throat.

View full abstract

In this study, we develop an effective noncontact technique for detecting rolling over in bed. We propose a new method for detecting rolling motion by measuring the current generated due to a change in the capacitance between a given electrode and the human body. The technique involves the detection of electrostatic induction current of the order of approximately sub-picoamperes flowing through the electrode that is placed at a distance of 1 m from a subject. A theoretical model is proposed for the electrostatic induction current generated due to a change in the electric potential of the human body. This model can be used to effectively explain the behavior of the electrostatic induction current flowing through the measurement electrode. We apply the noncontact technique to detect the timing of rolling over in bed. Thus, we could quantitatively estimate the timing of rolling over in bed under noncontact and nonattached conditions. Our technique enables easy in-situ detection of the timing of rolling over in bed.

View full abstract

To interpret the influence of whole-body vibration (WBV) on a seated human body, its vibration characteristics need to be clarified. Several previous studies have shown that differences in seated postures can change vibration characteristics such as the resonance frequency and the resonance amplitude of seat-to-head transmissibility and driving-point apparent mass. However, these studies did not fully express the seated postures of their subjects. Although the evaluation of human exposure to WBV is specified by ISO 2631, the seated postures for experiments are not specified in an ISO standard. To make good use of the results of human vibration experiments, a technical report on the description of seated postures exposed to WBV was published in 2012 and is still being discussed. In this study, we have measured seated postures in vibration experiments and investigated the relation between these postures and the resonance frequencies of transmissibility and apparent mass. A vertical random vibration of frequency 2-30 Hz was used in the experiment. The experiments were performed with two seated postures, an upright posture and a relaxed posture. The performance of a single regression analysis and a multiple regression analysis suggested that lumbar curvature is related to these resonance frequencies.

View full abstract

The most serious symptoms in head injuries by Shaken Baby Syndrome (violent shaking as child abuse) is acute subdural hematoma (ASDH). ASDH of infants is high mortality rate and leaves serious aftereffect. It is difficult to get accurate evidence from third parties since the abuse occurs in the home mainly. So, they, who work in medical institutions and polices, would rely on experience and intuition to determine the cause of head injuries. Therefore, in this study, we performed simulation analysis that reproduced the shaking action using a finite element model of infant head to give a scientific basis to the determination. We used 6-month-olds head model which constructed from adult head models and CT scan images of infant head. Input value was defined as the angular velocity and displacement of the head obtained from the vibration experiments with 6-month-olds dummy. ASDH is occurred by the relative rotational motion between the skull and the brain with a rupture of bridging veins, which connect skull and brain. Therefore, we evaluated the relative movement between skull and brain and measured the stretch ratio of bridging veins. Then, we compared the ratio with the threshold witch is rupture value.

View full abstract

The purpose of this study is to make the sensor system for capturing the movement of sprint running. The sensor system was constructed by the 3-dimentional acceleration sensor, the 3-dimentional gyro sensor, control processor and the operation device. Moreover, this sensors system has the software having the algorithm for dynamic calculation, and it can process the dynamic data on real time. In this study, we did an experiment to attempt the sensor system by capturing the running movement. As a result, the dynamic data of correct tendency was obtained. Furthermore, these data had represented parameters relating the running movement.

View full abstract

In the last symposium we reported that pull-up action enhanced (increased) the index of force effectiveness (IFE), which is defined as the ratio between the total force (FT) and the effective force (FE), when comparing to the conditions under push and preferred cycling during short-term bicycle exercise. However no significant difference could be observed in EMGs obtained from four leg muscles among three pedaling techniques. In the present study we, therefore, attempt to differentiate the EMG activities in eight leg and hip muscles during short-term cycling, and to elucidate the effect of long-term exercise on the change of IFE, oxygen uptake (VO_2) and EMG by using a newly developed cycle ergometer system in our laboratory. Four college cyclists performed 3 short-term exercise bouts for 3 min (Exp.l) and 3 long-term exercise bouts for 15 min (Exp.2) under three pedaling techniques; pull-up, push and preferred. In the Exp.l, it was reconfirmed that that IFE was the highest under pull-up pedaling and the lowest under push pedaling, although insignificant differences were observed in muscular activities. Furthermore, in the Exp.2 it seemed that IFE gradually decreased when VO_2 increased systematically from 5 to 15 min from the onset of exercise, whereas IFE remained a steady state when VO_2 kept constant. These results indicate that, in the nonsteady state exercise in VO_2, FT increased and thereby IFE decreased gradually, and thus the mechanical efficiency would be decreased.

View full abstract

A new optimization system of cycling driving forces was investigated in this paper. This system was composed of newly developed cleat shaped biaxial load cells which measure biaxial-forces of right and left leg independently, and evaluation program for pedaling-effectiveness and joint torques with link model of lower limbs. The new load cells were attached to the bottom of cycling-shoes instead of the plastic cleats. Cyclist was able to connect their cycling-shoes to pedals by the load cells. The sizes of load cells were almost same as plastic cleats (Shimano Corp) and measure the magnitude and direction of right and left pedal force using 16-strain gages, respectively. The analytical system solves the link model of human lower limbs to identify the positions and angles of each segment of lower limbs. The lower limbs model consisted of 3 segments, thigh, lower thigh and foot. The length of the each segment, length of crank and position of greater trochanter were supposed to be constant for computational calculation. From the lower limbs model, all position of every lower limb segment and joint torques were calculated by this system. For analysis of the pedalling-effectiveness, each pedalling force measured by the load cells were converted to forces on coordinates respective to tangential and radial directions of cranks. The pedal angle was calculated by the link mechanism of lower limbs. The pedalling-effectiveness and relationships between cycling driving force and joint torques were investigated.

View full abstract

In human gait motion analysis, which is one useful method for efficient physical rehabilitation, ground reaction force, kinematic and kinetic parameters are measured during walking. Recently, it is thought that the patients with walking disability including trans-femoral amputees must regain moving pattern by refined rehabilitation program using ground reaction forces, joint angles and joint moments. At present, intuitive gait training systems cannot be put into practical use adequately. For obtaining these data as the directly wearable gait measurement, in addition to a novel gait motion analysis system using mobile force plate and attitude sensor, split-belt treadmill instrumented force plate with a new concept for motion instruction based on biofeedback has been developed. However, they have not been synthesized yet as motion instruction system focused on the gait training in the past. In this study, ground reaction forces, kinematic and kinetic parameters applied on the healthy subject are measured by using the developed split-belt treadmill instrumented force plate, wearable gait motion analysis system and conventional gait measurement system simultaneously for the development and verification of motion instruction system. As a result of the experiments and consideration by their intercomparison, the patterns of ground reaction force, spatial information and each evaluation index by them are obtained as similar feature quantities among each measurement condition in cases of using instrumented treadmill, wearable gait motion analysis system and conventional measurement system. Finally, the effectiveness of the developed instrumented treadmill and quantitative evaluation concerning human locomotion on the instrumented treadmill by those data is validated.

View full abstract

In this study, we describe the analysis of human walking towards the development of biped robot. There are a number of previous studies on the behavior analysis of human. A way to get the skeleton information, an example of using the KINECT developed as a controller for the game available at low cost has increased in recent years. In this study, the examples of motion are normal walking, the left hemiplegia walking, robot walking and walking with operated smartphone. The measurement method, were taken by moving to match the walking speed of a person and the KINECT on the truck. In addition, we analyzed the eigenvalues by the singular value decomposition skeleton information. Result of the analysis were in the robot walking is most stable. As the result, it is possible to analyze feature quantity of the walking is obtained by singular value decomposition. It is believed that the application of this method, it would be utilized for prediction and prevention of falling during walking.

View full abstract

A shuttlecock used for badminton has an extremely complicated shape in comparison with other sport projectiles and quickly flips over after hitting by a racket. Although the flip of a shuttlecock is a fundamental behavior during badminton game, aerodynamic characteristics of the shuttlecock flip have scarcely been studied from engineering's point of view. Concerning the investigation of the shuttlecock flip, a computer simulation based on proper aerodynamic properties is a best tool. This paper describes a possibility of the flip simulation in which shuttlecock aerodynamic properties are acquired by using images of shuttlecock trajectory experiment captured by a high speed video camera without a wind tunnel experiment. Through the comparison between experimental and simulated results of shuttlecock trajectories, a fairly good agreement is obtained and the possibility of the flip simulation has been shown.

View full abstract

A badminton shuttlecock generates significant aerodynamic drag and has a complex flight trajectory. The objectives of this study were to measure the aerodynamic properties of feather shuttlecocks under a wide range of wind speeds and to investigate the aerodynamic stability for the pitch movement (rotation about lateral axis). In particular, measurements of aerodynamic forces were performed at high Reynolds numbers. The lift and drag characteristics of shuttlecock have the same tendency with and without spin rotation. On the other hand, the pitching moment coefficient is affected by spin rotation. The pitching moment for a rotating shuttlecock is larger than that for a non-rotating shuttlecock. Furthermore, a shuttlecock is aerodynamically stable for the pitch movement just after impact. It was confirmed that the aerodynamic stability of a badminton shuttlecock is related to the gaps between the slots located at the leg portion and the feather of shuttlecock skirt.

View full abstract

We investigate estimation methods of aerodynamic coefficients for a projectile by using characteristic quantities in its trajectory. One method is based on the quantities representing the whole shape of trajectory while the other utilizes local quantities such as curvature and/or torsion. In the former, the flight distance and the maximum height are measured, and the motion equation predicts numerical values of these quantities with measured initial condition and preset aerodynamic coefficients. Then the optimal combination of the aerodynamic coefficients is determined by minimizing the error between the measured and estimated values of the characteristic quantities. This method is applied to estimate drag and lift coefficients of a soccer ball in back-spinning, and the result shows that the averaged values of C_D and C_L are 0.205 and 0.237, respectively. In the latter method, the expressions between the aerodynamic coefficients and the geometrical quantities of trajectory are derived, which suggests that the piecewise quadratic interpolation on a trajectory provides the aerodynamic coefficients. This method enables to locally estimate the coefficients, and therefore clarifies the variation of the coefficients along a trajectory. Measured data for a table tennis ball is analyzed with the method and we obtain successfully the drag and lift coefficients in flight condition. The results indicate the qualitative difference of spinning effect in drag and lift coefficients.

View full abstract

A method of reconstructing the 3D trajectories of a ball with two unsynchronized cameras is proposed. Currently, the common devices for 3D sensing in sports match scenario are time-synchronized cameras. There, however, exist several difficulties to conduct it. The method proposed in this paper requires only two known 3D coordinates and unsynchronized cameras. The key feature of the method is to use balls for camera calibration and the estimation of time-shift of between a camera and the other camera. The method is experimentally verified that it could provide accurate 3D ball trajectories.

View full abstract

In Japan, there are two major baseball competitions, which are baseball and rubber-ball baseball. Players are often confused by the difference because many baseball players go through the transition between those competitions. Purposes of this study were to reveal the difference of the characteristics of the balls for baseball and rubber-ball baseball when those balls are hit by a metal baseball bat and to research experienced perception of the baseball players toward the difference. A bat swing robot was used for researching physical characteristics of those batted balls under stable condition with changing the vertical offset between the center of a bat and that of a ball. As a result, a rubber-ball recorded maximum range by smaller offset than a baseball and it also tended to generate larger vertical angle and smaller speed of the batted ball. Furthermore, the result of the robot test corresponded to the experienced perception of baseball players, which was revealed by a questionnaire.

View full abstract

The purpose of this study is to analyse the dynamic effects of soccer balls and the differences impact forces have on these balls. The subject under discussion is the balls that have different material surfaces and panel orientations. We chose four balls for this research: Cafusa, Jabulani, Theam Geist2 and Pelias. These soccer balls have 32 panels, 8 panels, 14 panels and 32 panels. The experimentation used a Kick-Robot which reproduces the same speed and position to repeatedly impact the ball. We attached a dynamometer to this machine in order to measure the impact force. We experimented four pattern of speed: 15m/s, 20m/s, 25m/s, 30m/s. The results suggest that there is any direct correlation between a maximum of impact force and a number of panels. But, when the Cafusa is compared with other balls, the impact force of Cafusa has a lower than any other balls because of the soft material surface. In addition to this, under the all speeds, the impulse value of Jabulani always shows the biggest value compare with other balls. We suggest that Jabulani has a special structure and a special surface.

View full abstract

According to the observations of pitched ball in real baseball game and aerodynamic characteristics clarified by wind tunnel experiments, there are many strange changing ball in baseball ball. In this research, special attention was focused on spinning axes direction, which oriented toward boll flight direction. There are no convenient pitching machines to be able to generate such kind of balls, easily. We had developed a pitching machine with pressurized air method into higher functional one, in which be able to generate purely oriented toward boll proceeding direction, with 2 and 4-seams ball arrangements. In this reports, we describe the strange characteristics of such kind of balls, and then some trial developments of the pitching machine. High speed camera images of shooting balls of 2 and 4-seams balls showed the success in this idea.

View full abstract

For professional badminton players, the highest initial speed of the shuttlecock exceeds 84m/s (300km/h), which is the fastest speed for a ball, racket or projectile sports. Many shuttlecock launcher machines have been developed, however it is difficult for the shuttlecock to be launched at speeds of more than 42m/s. In previous study, the launcher machine using the two turn rollers can launch the shuttlecock at the speeds of 52.8m/s. In this study, rubber material and new insertion equipment were proposed to rise up the highest initial speeds of the shuttlecock. From the results of the launcher experiments, it is attached guide pole makes the state of shuttlecock insertion. In addition, the launcher machine is used for the indoor type baseball batting machine, the launch conditions of the shuttlecock are examined.

View full abstract

In this paper, we propose a method to estimate impact forces from accelerations, and confirrm effectiveness of this method using simple models and marketing models. First, we measure frequency response functions of golf clubs by the experiment with an impulse hammer. Then, we really strike balls with a robot for striking and estimate the impact forces for different conditions of head speed and characteristic of balls. Finally, we calculate impulse of impact forces to evaluate consistency of estimated impact forces quantitatively and show that estimated results are effective for characteristic of golf clubs and balls.

View full abstract

The negative Magnus force was observed on a sphere at the moderate Reynolds number and the moderate spin rate which is defined by the ratio of the circumferential velocity to the free stream velocity. This region matches the forehand smash in a table tennis game according to the result of Taneda's experiments. To confirm the possibility of the existence of this negative Magnus force on the table tennis game, the wind tunnel test was conducted. As the result, it was observed at Reynolds numbers higher than 5.35 × 10^4. And we also provide a simple approximation of the lift and drag force to simulate a motion under the condition affecting a negative Magnus force.

View full abstract

Non spinning serve or shot exist as a technique in volleyball and soccer ball. Because the flight paths of these non-spinning balls are not stable. In the volleyball, it is called floater serve. Floater serves in volleyball and erratic path shots of the soccer ball are different in their speed area. In other words, they are the phenomena in a transition region on volleyballs and that in the super critical domain on soccer balls. It is thought that origin of each erratic phenomenon is different. In this study, three dimensional twin vortices were visualized behind volleyball using three-dimensional dynamic PIV and solved the origin of erratic motion on the floater serve. Quick motions of three-dimensional twin vortices were confirmed in the transition region on volleyball.

View full abstract

Traditionally, the soccer balls used in soccer tournaments had 32 pentagonal and hexagonal panels. Also, 14- and 8-panel balls have been used. Recently, new 32-panel ball (Cafusa, Adidas) with unverified aerodynamic characteristics are using. There is a need to understand the aerodynamic characteristics of a new 32-panel ball that used a variety football league. The purpose of this study was to analyze the basic aerodynamic characteristics of the Cafusa ball (32-panel) by using a wind tunnel. Also, we measured the orientations (Face A, B, C) of the aerodynamic forces for Cafusa ball. The critical Reynolds number of the Face A, Face B, and Face C was 〜2.6 × 10^5 (drag coefficient, Cd ≈ 0.12), 〜2.4 × 10^5 (Cd ≈ 0.16), and 〜2.4 × 10^5 (Cd ≈ 0.15), respectively. The flight trajectory simulation suggested that Face C has less air resistance in the high-speed region than the other Faces. It is considered that the critical Reynolds number of a soccer ball depends on the panel orientations.

View full abstract

It is known that low rotating or no-rotating balls have the erratic ball path especially in the recemt soccer balls. Aerodyanamic performance and dynamic velocity distributions of the balls wake were measured by 3 component load cell and dynamic PIV system on five types of different panel balls. As a result, the difference of drag coefficient of each ball was found especially in drag crisis regions. Three-dimensional twins vortices were found in the wake behind every balls. The magnitude of the jet stream velocity between each twin vortices was also found to vary according to the difference of the ball panel.

View full abstract

The "turbo-jav" which is used for the javelic throw in the junior Olympic games has four fins at its tail unlike a spear used for the javelin throw. In order to investigate the aerodynamic characteristics of the turbo-jav, we performed wind tunnel tests, throwing experiments and numerical simulations for the flight of the turbo-jav. In the wind tunnel test, we measured the drag force, lift force and pitching moment acting on the turbo-javs in a low speed wind tunnel at the flow speed up to 25 m/s. The experimental results showed that these aerodynamic coefficients are almost constant irrespective of the Reynolds number for given angles of attack when the flow speed is larger than about 12.5 m/s. The moment coefficient was found to decrease from zero with increasing angle of attack from zero. In accord with this property for the pitching moment, throwing experiments showed that the turbo-javs fly stably with oscillating angle of attack around 0. The flying distance, the orbit and the variation of angle of attack for turbo-javs launched by a launcher agree closely with the numerical simulation performed based on the wind tunnel test. The turbo-javs launched by the launcher are found to fly without rolling whereas the turbo-javs thrown by athletes rotate considerably. A comparison of the throwing experiments by athletes with those by the launcher suggested that the turbo-javs flying without rolling could reach farther than turbo-javs with rolling for the same initial conditions.

View full abstract

A flying disc can fly through the air because of the combination of the lift and drag forces by the oncoming air flow. Actual fight conditions were confirmed to perform the wind tunnel experiment beforehand. In order to clarify the mechanism of flight of flying discs, the flow field structure and the fluid force were investigated on non-spinning and spinning conditions. In the fluid force measurement, lift and drag forces were taken by varying wind speeds, spin speeds, and angle of attack. Drag and lift forces were found to increase as spin increased. The angle of attack on the maximum range of lift-drag ratio or glide ratio was found to be wide from 6 to 13 degrees which was suitable for a long distance throwing. Using a smoke wind tunnel, flow visualization around the disc was performed in order to understand the effect of disc spin. It was found that spin enhances lift force by attracting the Coanda effect on the trailing edge.

View full abstract

In this report, aerodynamic characteristic such as lift and drag of official rubber-balls used in the game of the baseball are studied experimentally. And the aerodynamic characteristic of these rubber-ball is compared and is examined with the aerodynamic characteristic of smooth sphere and sphere with dimple and the Major League ball. In addition, the aerodynamic characteristic for seam angle and spin rate ratio ratioα (=V/U, V: peripheral velocity of test balls, U: flow velocity)is also clarified. And, the flow pattern around the test balls are visualized by the spark tracing method. Following conclusions were got from these results. (1) The dimpled rubber-ball has a critical region where the drag coefficient decreases in the same way as the smooth surface balls. (2)Depending on the surface structure of test balls, the aerodynamic characteristics differ significantly. When dimples are added to the balls with seams, the critical region moves toward the lower Reynolds number side, but the minimum drag coefficient increases. (3)About the rubber-ball and Major League ball, C_D shows the almost same values without rotation. However at the rotational state, C_D of the Rubber-ball is lower than that of the Major League ball . (4)The values of C_D take different values depending on type A〜E and become large as α increases. The values of C_L stand in a same line which rises as α increase.

View full abstract

We conducted the experimental and numerical trajectory analysis of the baseball and investigated the aerodynamic characteristics acting to the baseball. The optical images of the ball released from the pitching machine are taken by the high-speed camera and the translational and rotational motions of the ball are computed by the image processing. In the numerical analysis, the flowfield around the ball is assumed as the ideal fluid and the motion of the sphere without the seam are computed. We compared the aerodynamic characteristics of the baseball with those of the ball used in the lacrosse to investigate the effects of the seam to the motion of the baseball. The experimental results showed that those effects induced the gaps of the forces acting to the ball and of the trajectories between them. Although the aerodynamic coefficients are measured under the steady flow condition in general, they are modified as the parameters for the unsteady flow from the differences between the experimental and the numerical results.

View full abstract

To evaluate the motion of a curling stone on the ice, a velocity change and a curl of the stone have been experimentally analyzed. In 2012, we observed the motion of a curling stone and measured the positions and rotating angles during the motion on the ice by image processing of sequential images of the curling stone obtained by CCD cameras installed over the curling sheet. In this study, we evaluated a velocity change and a curl with acceleration vector, which is decomposed into a tangential component of the direction of velocity related to a velocity change, and a perpendicular component related to a change of direction of the motion, using the data of experiment in 2012. Characteristics of the motion of a curling stone related to the velocity and angular velocity are investigated with parameters such as the tangential and perpendicular acceleration of the stone.

View full abstract

In this study, I have studied aiming to curling robot can win a human. In this paper, we manufacture of curling stone delivery robot, to construct a motion model of Stone, the manufacture of the simulator using the motion model of Stone and we experiment with stone delivery integration of these further. Results, curling stone delivery robot can perform a delivery reproducible, When the simulator was within the limits of the delivery parameter used abundantly by actual game, reality and a near result were obtained in general. Further, it was possible to integrate the curling stone delivery robot simulator and to deliver a stone any point.

View full abstract

The motion of a curling stone is controlled by the frictional interaction between its running band and pebbles on the ice sheet. In this paper more detailed results of computations of path trajectory, curl ratio, and effects of sweeping, pebble density and the level of ice sheets are reported. Curl ratio is a convenient quantity to specify definitely the direction of a stone to move at a given translational and angular velocities. It increases with the decreasing translational velocity and increasing angular velocity. Sweeping can be reasonably explained as warming of ice surface. The increase in the number density of pebbles leads to the decrease in the pressure acting on pebbles, resulting in the increase in the ice friction coefficient and curl ratio. Trajectories at various inclined ice sheets are computed and discussed.

View full abstract

This paper describes the motion analysis of the Japanese bow made from carbon fibers with the linen string for archery. The final target of this study is to establish the realistic relationship between human body and the bow with the string in giving instruction and to propose a suitable text book for players to keep healthy. In this case, a vibration characteristic of the bow with the string is noticed due to experiments and calculations by the Rigid Motion Analysis. The calculation model consists of rigid bodies and rotational springs. When the string of the bow is drawn and released, displacements and vibration characteristics of the upper and lower of the bow are measured by video-camera and calculated by computer. A good coloration between experiments and calculations is taken. It is considered in the next step to make human body models with some kinds of the skeleton.

View full abstract

Some previous studies have reported the consistency of the model calculations of the impact force, angle of reflection, coefficient of restitution, and the ball speed and angular velocity after impact. The others have reported the theoretical analyses of the effect of friction for impact if the ball and the flat surface have friction, or not. But only few data from the previous research have reported the experimental measurement of the impact of the soccer ball, which is pressurized spherical elastic shell, against the flat surface which has friction. This study is primarily intended to find out the property of the characteristics of the friction force which is formed by the collision of the soccer ball against the materials used for the goalkeeper gloves, changing the impact speed from 10 to 30 m/s. The soccer balls shot out by the 3 rotors machine keep the angular velocity 0 and come into collision on the angle with the rectangular-shaped latex formed material used for the goalkeeper gloves on the force plate. The impact force is measured vertically and horizontally from the force plate. Getting the averaged impact force curves, we discussed about the feature of the friction force between the soccer ball and the latex formed material. In addition, we measured the surface texture of the latex formed material by using the laser displacement meter, and discussed the relationship between the friction force and the surface texture.

View full abstract

The purpose of this research is to clarify the required roles and techniques of goalkeepers in top-level games by analyzing their plays in 2010 FIFA World Cup South Africa. In addition, this research attempt to provide evidence that would help coaching in football. In conclusion, goalkeepers' major play appeared to be "Attacking". They make positive efforts to support their teammates. The other data verify that goalkeepers should have techniques that filed players possess. This is because that they play a role in successful offensive play in a match. That is to say, goalkeepers are ought to have the same training as field players do.

View full abstract

The aim of this study was to examine the cognitive processes that underpin the performance of soccer players on the basis of the perception-action cycle. Decision making tasks were undertaken involving 16 soccer players with different proficiency levels. We combined an eye movement measurement with a verbal report to identify in detail the cognitive processes during the task. Subjects attached an eye movement measurement device to themselves to measure their eye movements during this task. After each sequence, subjects were interviewed regarding "the choice the pass" and "about the recognition of the situation". Results indicated that expert players were able to pass to the intended place more precisely than the sub-expert players. Expert players fixated on more objects for a shorter duration. Moreover, expert players fixated on an important place for a long time before passing the ball. Additionally, expert players generated substantial high quality information about the recognition of the situation. Overall, the study suggested that expert players employed more exploratory strategies than sub-expert players, such as fixating longer on an important place and identifying in the situation.

View full abstract

Judo is the martial arts that can lead to severe head injuries. Bruising on the back of the head and acute subdural hematoma commonly occur in beginners thrown by Osotogari. Sports-related head injuries were studied by using head protective equipment, which has been evaluated previously. However, these studies treated the head as a rigid body, and evaluated only the impact on the head. As these studies did not consider the behavior of the neck in soft impacts - a major factor in acute subdural hematoma - their utility is limited. Therefore, in the present study, we examined the efficacy of protective equipment that suppresses neck extension, equipment that protects the head, and equipment with both the neck and head. Three shock-absorbing materials (hard urethane, soft urethane, low rebound material) were used. The cranial model used polycarbonate to enable the observation of the behavior of the brain, whereas the brain parenchyma model used silicone gel with similar physical qualities to the brain. Black marker was applied to the surface of the brain parenchyma model and the cranial model. The experimental apparatus was collided while maintaining the velocity of the head at 3.5 m/s. The behavior of this collision was captured by a high-speed camera and relative changes in marker distance were measured. The results indicated that the equipment with both head and neck protection suppressed the relative displacement. Thus, while developing equipment in the future, not only protection the head, but also suppression of neck extension should be considered.

View full abstract

Judo has high mortality rate than other sports, and the most common cause of death has been reported to be acute subdural hematoma caused by osoto-gari (large outer reap). The purpose of this study was to analyze the head movement of the uke (the person being thrown) of osoto-gari for examination of the mechanism of acute subdural hematoma caused in judo activity. In our experiment, the uke wear a headgear equipped with angular rate sensor to measure the angular velocity in the sagittal direction of the head of the uke at the time when the tori (the person who throws) threw by osoto-gari and calculated the angular acceleration. We used a high-speed camera to record behaviors of the tori and the uke. No marked change in the angular acceleration was observed when the uke was in the air from the time when he was thrown to the time when he did ukemi (breaking the fall). The peak angular acceleration was observed just after the palms made contact with the floor. Head movement of ushiro-ukemi (rear breakfall) was analyzed similarly. Also, in ushiro-ukemi, the peak angular acceleration was observed just after the palm made contact with the floor. However, each value was smaller than the threshold value of rupture of a bridging vein. The results showed that having the hand make contact with the floor and reduced the angular acceleration of the head and prevented excess rotation backward.

View full abstract

American football (AF) is characterized as a collision sport and it has been reported that there are a lot of injuries including catastrophic injuries. Many reports state that head injury has occurred in about 10% of the whole, and especially the incidence of a brain concussion is very high. Biomechanics research to analyze a mechanism of the brain concussion by video analysis has been done since the 1960s. Then, several collision experiments to investigate the linear and rotational accelerations acting in the head during a collision in the actual field have been conducted since 2003. However, it is not clear the relationship between the magnitude of the linear and rotational accelerations and the severity of concussion. Therefore, the effect of the helmet itself at the time of a collision needs to be reconfirmed. The purpose of this study is to examine both the action forces exerted on the helmet at the time of a collision and the reliability of a new method with strain gauges. The specially made helmet which was equipped with the strain gauges was placed on the force plate and another helmet was dropped from the top to the helmet. We could confirm the estimated value of acting force to the helmet from the force confirmed from the strain gauges, and also confirmed the reliability of the new method in the collision tests in vivo in the near future.

View full abstract

Micro sensors have begun to be used in the scientific research of safe improvement and technical analysis of rugby. This paper aims to develop a system to measure the impact forces of contact plays using an acceleration and gyro sensor. The acceleration vector provided from a sensor uses a peculiar local coordinate system. Therefore, the acceleration vector of the local coordinate system is converted to the acceleration vector of the absolute coordinate system by Rotation matrix. The displacement and the velocity are calculated by integrating accelerations of the absolute coordinate system. The impact force is calculated from the relationship between the momentum increment and the impulse. This article reports the practical skill experiment that measured the impact forces of the contact plays. The experimental results clarified the quantitative error and problems in the measurement using the inertial sensors. The measurement success rate was 50% with velocity, 40% with impact force and 20% with the coefficient of restitution, respectively.

View full abstract

The top players of field hokey experientially know that high restitution area of their hokey stick exists not on the head but on the position slightly shifted to grip end. They would have to swing the stick horizontally with low posture to hit the ball near the area when strong and high speed balls were needed in the game. Therefore, we have been developing a new hockey stick that has high restitution area on the head. The mass distributions of sticks affect the positions of the 1st modal node of vibration and center of percussion has been found. The area on the high coefficient of restitution may be related to the positions of the 1st modal node of vibration and center of percussion. In this study some experiment using sticks with the various positions of the modal node and the center of percussion controlled by the mass distributions has been carried out. Furthermore a hockey ball model was newly proposed for FEM analysis. The results of the FEM simulation closed on the results of our previous experiment.

View full abstract