This paper describes a method for characterizing baseball bat swing by using inertial sensors attached on a bat. The inertial sensor is consisted of a tri-axial accelerometer, tri-axial angular rate sensor (gyro) and tri-axis magnetometer. The inertial sensors were attached on the head of bat and on the tail of grip. Two healthy male subjects were participated in our study. One was skillful baseball player and the other was a beginner. Their swing motion was measured by camera based motion capture system and the sensory bat, in conditions of normal swing and with a load of 400 g weight ring on the bat. Experimental result showed that swing trajectories were different between skilled and unskilled subject. The difference was represented in measures of the inertial sensors as largar magnitudes of linear acceleration on the grip than that of the bat head during in a swing. Comparing normal and weighted swings, differences of swing timing were also detectable from the sensor data. This simple method using inertial sensors for bat swing evaluation is possibly useful for motion assessments outside of laboratories.
