In the field of machining industries it is always required to improve the accuracy of precise products, die and molds. The feed drive system for the machine tools consists of an AC servo motor, an amplifier and rolling elements etc. It is well known that the nonlinear behaviors of the rolling elements influence the motion accuracy of the feed drive system. However, in spite of the analysis of static behaviors have been done, the dynamic behaviors are not so examined. Our special interest is how to control the nonlinear behaviors of the rolling elements and to operate the feed drive system with high accuracy. In order to model the nonlinear behaviors of the feed drive system, we measure the transient response when the step inputs of microscopic displacement are input to the AC servo motor and the detail analysis will be done. Experimental results show that the step responses become slow as the input displacement becomes microscopic. It means that with the ball bearing built into the AC servo motor used to feed driving system have the nonlinear behavior in microscopic displacement range.
