Abstract
A knocker robot was developed. This robot can control the swing speed and the swing angle of a bat, and also the position of a ball. The ball speed just hit by the bat was measured by using a high speed camera. The trajectory of a ball can be simulated by a differential equation model for which the data from the high speed camera were used. The relationship between the swing speed and the initial ball speed, and also that between the initial ball speed and the flight distance were studied by experiments and simulation.