（以下、）の材種と流通の現状と変遷を明らかにするため、国内主要工場6 社への聞き取り調査及び文献調査を実施した。材種に関しては、1979 年に国内製造されたはほぼ全量が北海道産材であったが、2005 年頃を境に、北海道産アオダモから北米産・中国産メイプル、中国産モウソウチクへと移行し、現在は外材が少なくとも約70%を占めていると推計される。流通に関しては、以下の点が明らかになった。外材の増加により、1985 年に比べ、北海道の材工場数が激減した。工場については、メーカーの下請けを維持する工場とメーカーの下請けから脱却する工場の二極化が起こっている。さらに、1985 年には、国内で加工・製造されていたが、現在では、材加工の多くが海外へと移行し、製造工程の一部も中国へ移転し始めていることが明らかになった。また、販売方法としては、インターネット販売が新たに登場した。このような状況で北海道産アオダモによる生産を継続するためには、アオダモの育成だけではなく、原産国表示によるブランド力の維持も重要ではないかと考える。

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Recently, a variety of baseball bats are sold. The materials used in baseball bat are made from the wood, the aluminum or the FRP. The percussion performance is one of the keys to its selling well. The character called sweet spot is used to evaluate the percussion performance. But the relations between the sweet spot position and mechanical characteristics are unclear. First, sweet spot position is theoretically pinpointed by the modal analysis and the energy theory. The closer collision is to the node of mode, the more rebound. And the closer collision is to the center of gravity, the more rebound. Next, the theory is tested by experiments. The first node and second node are pinpointed by the experimental modal analysis. The most reflective position is pinpointed by the collision experiment. In conclusion, the first node should be used for the sweet spot position. The center of purcussion is poor markers of the sweet spot.

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The purpose of this study was to investigate the effects of the characteristics of baseball bats on swing. The subjects were five skilled baseball players. An experimental bat was provided, which made it possible to set up nine conditions for the position of the center of gravity and the mass. The behaviors of the bat during swings were analyzed with DLT method using two cameras, and the three-dimensional kinematical data were calculated at the impact to ball and during swinging the bat. The main results were as follows :1) There were a few cases in which the angular velocity of the bat at the time of impact had an effect on the position of the center of gravity or the mass of the bat.2) In the case in which the characteristics of the bat had an effect on the swing speed at the impact, it had a favorable effect on the behavior of the bat during swing.3) It was not found that the characteristics of the bat had an effect on the accuracy at the impact.

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    The purpose of this study was to investigate the effect of the mass and position of the center of gravity of a baseball bat on its hitting performance. Twelve skilled baseball players were used in the study. A bat was developed for which the mass (869.2 - 912.4 g) and position of center of gravity (30.1 - 32.8 cm : the distance from bat head) could be adjusted. In this experiment nine different settings for the position of the center of gravity and the mass were used. The motion of the bat during swings was analyzed by the three-dimensional direct linear transformation method using two cameras, and kinematic data were calculated for the moment of impact of the bat with the ball and also for the entire hitting process. The main results are summarized as follows:
1) The head velocity was greater when the subjects swung a baseball bat with the center of mass located near the grip than when they swung another baseball bat with the center of mass located far from the grip.
2) For all the baseball players, the bat′s mass did not affect the head velocity of the bat at impact.
3) The head velocity was greater when the subjects swung a baseball bat with a larger moment of inertia about the axis passing through the grip than when they swung another baseball bat with a smaller moment of inertia.
4) In some cases, the mass of the bat had a significant influence on the angular velocity on impact for a player who had a translational swing. In this case, the characteristic of the swing type was shown to affect hitting performance.
    When choosing a suitable bat for each player, the swing style of the player needs to be considered. This finding suggests that when characterizing bats, not only should the mass of the bat and the position of its center of gravity be used as indexes, but also the moment of inertia, which is related to the grip of the bat, should be employed.

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The purpose of this study was to examine the factors influencing the behavior of the baseball during and after the impact with a wooden bat. A finite element approach was used to model the behavior of a baseball and a wooden bat at the impact and the linear and angular velocities of the ball after the impact were determined for given sets of impact condition. The simulation outcome was validated with 22 sets of actual measurements taken during a “free batting practice” performed by the members of a collegiate baseball team.

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Many studies on baseball bats have been carried out in the world. And a lot of useful knowledge for development of bats, e.g., coefficient of restitution, trampoline effect and so on, have been obtained. However, effect of clamping conditions on hitting performance has not been clarified yet. Therefore, we have developed an evaluation system for coefficient of restitution on baseball bats using three kinds of clamping devices for bats, that is, “rigid clamp”, “rotating-free clamp”, and “free support”. In this paper, the evaluating system and some examples of experimental results have been reported. We concluded that differences in clamping method of metal baseball bat scarcely affected evaluating results of coefficient of restitution on hitting. The rotating-free clamp is well suited to the system from the viewpoint of the simplicity of experimental operation and adequacy of the data.

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Impulsive force acting when the ball is hit with a baseball bat is interesting from the field of sports engineering. This study intends to develop an impulsive force sensor which can be attached to a column part of the baseball bat. The pipe surface sensor is a pressure sensor suitable for the measurement of high speed impulsive force. The pipe surface sensor consists of a thin pad sensor, a cover-plate and metal adhesive tape. The metal adhesive tape plays a role to wrap the sensor and cover-plate and fix these together to the bat tightly. First, a friction removal mechanism in contact interface, a bendable sensor configuration and a method of sensor installation on the surface of the pipe are discussed. Then, prototype sensors that can be installed on a pipe with diameter of about 70mm are made. The performance of sensor is investigated by the pipe punch test and the ball drop test. Then, the impulsive force is measured by the test that a batter hits the ball which the pitcher threw. A metal bat and a hard ball are used for the experiment of hit and bunt.

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長軸方向への力は、ヘッドスピードと密接に関係しており、その大きさに対する貢献度は約70%であると報告されている。しかし、長軸方向への力とバッティング動作との関係は明らかにされておらず、長軸方向への力を生成するのバッティングの運動学的要因は不明なままである。そこで、本研究では、逆動力学演算ではなく、に作用する力を推定することで、長軸方向への力を生成するバッティング動作の解明を試みた。大学硬式部に所属する学生選手30名の最大努力によるティーバッティング動作をモーションキャプチャーで記録した。Sprigings et al.（1994）の方法を応用して、の加速度を算出する式を導出し、得られた加速度にに作用する力を推定した。その結果、長軸方向への力は、手関節の角速度（49.7%）、骨盤の角速度（21.6%）、体幹関節の角速度（16.0%）、肩関節の角速度（9.3%）によって概ね90%が生成されることが明らかになった。

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    The present research aimed to characterize the baseball bat swings of high-school baseball players. Despite the difficulties associated with establishing a classification standard for the quantitative evaluation of bat swings, the acceleration applied to the bat was measured during high-school baseball players' swings. Subjects were 53 high-school baseball players who swung an experimental bat. The knob of the experimental bat was equipped with accelerometers, which measured the three components of linear acceleration and the three components of angular acceleration applied to the bat. Classification of players' swings based on the acceleration applied to the bat revealed the following results.

    (1) Evaluation of players' swings based on the acceleration applied to the bat was possible. This evaluation clarified methods for applying force and torque to the bat during a swing. (2) Based on changes in acceleration and the angular acceleration applied to the bat just before impact, the swings of these players were classified into nine categories. (3) These nine categories were further consolidated into three types based on changes in angular acceleration. In one type, angular acceleration of the bat decreases before impact. However, all subjects were divided into the remaining two types, in which angular acceleration of the bat increases before impact or angular acceleration of the bat does not increase before impact. These results suggest that classification of bat swings is possible.

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　本研究の目的は、

のダイナミクスを分析し、ヘッドの加速メカニズムについて検討することであった。アマチュア選手99名の最大努力によるトスバッティング動作をモーションキャプチャーシステムで記録し、のキネマティクス的変数を算出した。加えて、逆動力学法を用いてグリップに作用する力およびトルクを算出した。スイング開始以降、グリップ周りにスイング方向へのトルクが発揮され、の回転エネルギーも増大した。しかし、インパクト直前からトルクの発揮は減衰し、インパクト時にはスイング方向とは逆向きのトルクに転じた。インパクト直前からはの並進エネルギーの増大が顕著であった。スイング動作を通してヘッドの曲率半径は単調増加の傾向を示し、インパクト直前におけるヘッドスピードの2乗に極めて強い相関関係が認められた。これらのことから、のバッティングでは異なるタイミングでヘッドを加速させていることが推察された。

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The restitutional property is one of the most important factors on the regulation baseball bats. When balls collides with baseball bats, local deformations are caused on the attack surface. These local deformations have the great influence upon the restitutional properties. In this study, the relationship between the local deformations and restitutional properties is made clear by using the finite element method. In order to make the designing guide of baseball bats, the relationship between the local deformations and mechanical properties of the baseball bats such as flexural and lateral compressive stiffnesses is investigated. The application of fiber reinforced plastics (FRP) to regulation baseball bats is also examined. This application can give the more extensive approach to the designing of baseball bats, compared with conven tional materials such as wood and metals, because the FRP has the high specific stiffness and the anisotropy.

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The purpose of this study was to clarify the kinetic features of each hand under conditions of different hitting-point heights (high, middle, and low) in the baseball tee-batting. Twenty-three collegiate male baseball players’ motion were captured by VICON-MX system (12-camera, 250Hz), and kinetic data at each hand were collected by using an instrumented bat equipped with 28 strain gauges (1000Hz). Three kinds of tee-batting heights were set for each subject based on the upper and lower limits of the strike zone according to the baseball rule. A moving bat coordinate system was defined to compare the characteristics of kinetic variables with respect to the different hitting-point heights. The vertical displacements of the ball hitting-point on the bat were dominated mainly with translational movement of the bat. The mechanical works of the vertical component of the bat longitudinal force of each hand show positive and greater values under low height condition than those under other conditions during down swing phase. The negative works done by the moment of each hand about the bat longitudinal inclination axis also show a similar tendency of the works of the bat longitudinal force at each swing phase. In addition, the peak values of coupled force about the bat inclination axis were observed in the latter half of down swing phase, and the component of coupled force was greater values under high condition than those other condition. These results indicate that the bat longitudinal force is a great contributor to adjust the translational movement of bat in the vertical direction, and the coupled forces and the moment about the bat inclination axis control the rotational movement of bat.

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　In baseball batting, rotation around the long axis of the bat, know as " rolling ", has been observed. A batter who can attain a higher rolling speed before ball impact can achieve a higher rotation speed of the struck ball, which increases the ball’s flight distance. It has been suggested that batters who swing the bat with high nutation can attain a high rolling speed. The purpose of this study was to investigate the effect of instruction aimed at increasing the rolling speed in baseball batting. Ten batters performed tee-stand batting under 2 conditions: a usual swing (CON1), and a swing after being instructed to position the bat vertically, and then swing by rapidly lowering the bat head (CON2). The three-dimensional motion of the bat was measured using a small accelerometer and gyro sensor attached to the grip-end of the bat. This sensor was able to measure the swing speed, swing time, rolling speed, swing angle (angle between the bat head velocity vector and the horizontal plane) and vertical angle of the bat (angle between the long axis of the bat and the horizontal plane) before ball impact and the swing trajectory from the start of the swing until ball impact. The rolling speeds employed were 726°/s (CON1) and 854°/s (CON2). The rolling speed for CON2 was significantly higher than that for CON1 (p <0.05). On the other hand, there was no evident difference in swing speed between CON1 (30.1 m/s) and CON2 (30.2 m/s), nor were there any differences in other swing parameters before ball impact. Batters who swung the bat at a high nutation speed in response to instruction increased the rolling speed, but those who were unable to change the swing trajectory and nutation speed failed to change the rolling speed. These results indicate that batters increase the rolling speed without changing swing parameters such as swing speed, swing time and the vertical angle of the bat in response to the above instruction.

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本研究は，打者が予めボール速度がわかっている条件（球速提示あり）とわからない条件（球速提示なし）において，球速の異なるボールに対する打撃動作の特徴および打撃の時間的調節に及ぼす動作の影響を検討することを目的とした．球速の異なるボール（85-87km/h，105-107km/h，125-127km/h）を被験者に打撃させ，3次元自動動作分析システムを用いて動作を計測した．速度および打撃の正確性を表す指標を算出するとともに，打撃動作における体幹部の回転運動と身体重心の並進運動についても検討した．その結果，球速提示あり・なしに関わらず，打者はボール速度が大きい場合，身体重心移動距離を小さくし，また体幹の捻りが最大となる時点からインパクトまでの上胴の回転動作範囲を小さくしていた．このことから，打者は球速提示あり・なしに関わらず，ボール速度の判断を行った後にボール速度に応じて打撃動作を調整していることなどが示唆された．また，球速提示なしでは，踏出足接地から下胴部の角速度が最大値を示す時点までの時間を調整することによって異なる速度のボールに対するタイミング調節を図っていることなどが示された．

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本研究はに関する研究である.高校はスポーツ用品としては主流製品といえる.に関する研究はthe American Society for Testingand Materials(ASTM)等で進められ(1),特に打撃性能に関する研究が盛んである.金属は打撃位置によって打撃性能が異なり,最も反撥する部位ある.その部位はスウィートスポットと呼ばれている.従来の打撃性能に関する研究の中でこのスウィートスポットという言葉は度々用いられるが明確な位置と定義に関してはあまり研究されていない.本研究の目的は振動学の見地からこのスウィートスポットの位置の特定と定義付けを行う事にある.

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本研究では，球速の異なるボールに対するの打撃動作の特徴を明らかにすることで，打撃の正確性に影響を及ぼす動作要因について検討することを目的とした．球速の異なるボール（ 75km/h，100km/h，125km/h）を被験者に打撃させ， 3次元自動動作分析システムを用いて動作を計測した．打撃の正確性を評価する指標としてインパクト角を用いて，身体の並進および回転動作と打撃の正確性との関連について検討を加えた．その結果，ボール速度が大きい条件（ 125km/h）においては，身体重心の並進移動距離を小さくするとともに，上胴部およびの回転動作範囲を小さくすることが打撃の正確性を高める動作であると考えられた．さらに，体幹の捻り角度および捻り戻しの角速度の最大値にはボール速度条件による有意な差は認められなかったため，これらの動作はボール速度に関わらずスイングに必要な動作であると考えられた．

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