抄録
The baseball's coefficient of restitution (COR) has been regulated by the Nippon Proffesional Baseball (NPB) for a regular season game in the first team of professional baseball players. If a ball impacts a rigid wall at 75 m/s, the ball's COR makes 0.4134 a desired value. The impact point of the ball is uncontrollable by the COR measuring method using a pitching machine. Since the surface form of a ball is not constant, it can be considered that the COR is influenced by the ball's impact point. In this study, the impact experiment of a ball for a rigid body wall was examined, and the ball's impact point was controlled using a light gas ball canon and a ball sabot. The effect of the ball's impact point on the COR was also investigated. The ball's impact points were the stitches part and the cowhide part (between stitches of the ball). As the results, the COR of the stitches part was higher than that of the cowhide part, and this difference increased with decreasing impact velocity of the ball. A t-test was performed to evaluate the difference between two CORs at a low impact velocity. Consequently, a clear difference was noticed between them. Furthermore, when measuring the impact load with a load sensor and deformation of ball, the absorbed energy was observed that the stitches part became lower than that at the cowhide part.
