Machine tool having function of detecting contact between tool and workpiece

A machine tool in which movable axes are composed of linear axes of X-, Y- and Z-axes, each driven by a linear motor, and a rotary B axis driven by a rotary motor, position detectors for detecting respective positions of the linear axes comprise linear scales each having resolution of 10 nanometer or less, a position detector for detecting a position of the rotary axis comprises a rotary encoder having resolution of 1/10,000 of a degree or less, each of the movable axes is supported by a fluid bearing, and a machining tool is moved relative to a workpiece by driving the movable axes so as to perform ultra-precise machining on the workpiece by means of the machining tool, said machine tool comprising;

• position deviation detecting means for detecting position deviations which are differences between commanded positions to the movable axes and the positions detected by the position detectors;
• contact point detecting means for scanning the surface of the workpiece by moving the machining tool relative to the workpiece by driving the movable axes so as to detect contact between the machining tool and the workpiece based on the position deviations detected by said position deviation detecting means, and for automatically setting and storing positions of the movable axes at the time of detection of the contact as the start point of the machining;
• and
• retreating means that retreats the machining tool away from the workpiece using the movable axis on which the machining tool is mounted when the contact is detected.