Method and apparatus for measuring a workpiece

Abstract

A numerical controlled machine tool provides a detector which produces a detecting signal when it is brought into contact or out of contact with a workpiece for measuring same. A driving device relatively moves the detector with respect to the workpiece, and a position detecting means for detecting the position of the detector. The numerical control device provides a signal corresponding to an amount by which the detector is moved with respect to the workpiece and causes the driving device to stop in accordance with the detecting signal. In operation, the numerical control device detects when the detector contacts with the workpiece while moving at a first speed, and applies a stop signal which is produced from a detecting signal given by the detector. The detector is then moved in a direction away from the workpiece at a second speed by a distance which is either larger or smaller than the distance by which the detector moved and stopped after the first detecting signal was produced. The detector is then further relatively moved either away from or towards, respectively, the workpiece at a third speed smaller than the first and second speeds. A detecting signal is again produced when the detector is brought into contact with the workpiece while moving at the third speed, and the contents of the position detecting device are read out when the detecting signal is produced while moving at the third speed is read out.