Control method for NC machine tool

摘要

A control method for an NC machine tool is provided which ensures a high precision of the contouring control, and allows for extension of the drill life, and reduction in machining time. The control method comprises: generating an operation command signal on the basis of the machining program and a time constant; generating a velocity command signal by multiplying a deviation of a present position signal fed back from the feed drive system (106) from the generated operation command signal by a position loop gain; generating an electric current command signal by multiplying a deviation of a present velocity signal fed back from the feed drive system (106) from the generated velocity command signal by a velocity loop gain; and controlling a drive motor of the feed drive system (106) on the basis of the generated electric current command signal for driving thereof, wherein a machining mode is determined from the machining program and, if the machining mode is a drilling mode, at least one of the operation command signal, the velocity command signal and the electric current command signal is modified when the feed drive system (106) is driven to be retracted opposite to a drilling feed direction.