Impact Response Measurement of a Bamboo Sword “Shinai”

Abstract

Impact response of a bamboo sword “Shinai” which is a practice sword used in a Japanese traditional fencing and has an unique and simple structure of light-weight bamboo plates for moderating the impact force to the human body, is accurately measured by means of modifying the Levitation Mass Method (LMM). In the method, a mass, which is levitated with an aerostatic linear bearing and hence encounters negligible friction, is made to collide with a bamboo sword under test. During the collision, the Doppler shift frequency of a laser beam reflecting from the mass is accurately measured using an optical interferometer. The velocity, position, acceleration, and inertial force of the mass are calculated from the measured time-varying Doppler shift frequency. The measurement results show that “Shinai” considerably moderates the impact force and its unique structure might be effective for robotics and automobiles to moderate the impact force acting to the human body in the case of accidents.