抄録
The purpose of this study was to quantify the dynamical roles of racket shaft elasticity during badminton smash motion. The racket shaft was divided into a set of rigid segments connecting to its adjacent segments via virtual joints with rotational springs. The deformation of racket shaft was approximated by using a 2nd order polynomial function from measured data during swing motion. The contribution of the joint torques to the racket head speed was obtained from the equation of motion for the system. Furthermore, with use of the equation, a recurrent equation with respect to the expanded generalized velocity vector, which consists of generalized acceleration and velocity vectors and the time integration of the velocity vector, was derived to calculate the contribution of the joint torque terms, external joint force term, and gravity term to the generation of the expanded generalized velocity vector. In order to realize stable numerical calculation for stiff system, the Newmark-beta method was used at the computation of recurrent equation. From the results, motion dependent term (M.D.T.), which plays significant roles for the generation of racket-face speed, was generated by shaft restoring torque at the middle phase of swing, and by joint torque term toward the impact. The shaft deformation was caused by wrist radial-ulna and shoulder internal-external rotation joint torques. These results indicate that racket face was accelerated by wrist and shoulder joint torques which generated M.D.T. by bowing racket shaft.
