Method and apparatus for discriminating cutting state from non-cutting state in machine tool

An apparatus for discriminating a cutting state from a non-cutting state in a machine tool wherein a workpiece is cut with a cutting tool, comprising:

• a plurality of vibration sensors which detect vibrations of different frequency bands, respectively, which are produced during cutting of the workpiece by the cutting tool;
• and
• discriminating means for judging that the workpiece is being cut by the cutting tool when levels of output signals generated from at least two of said vibration sensors are higher than respective predetermined threshold levels, and for judging that the workpiece is not being cut by the cutting tool when the level of an output signal generated from less than two of said vibration sensors is higher than a predetermined threshold level, one of said plurality of vibration sensors being an acoustic-emission sensor which detects an elastic wave of a high frequency band that is generated due to breakage or elastic deformation of the workpiece or said cutting tool.

An apparatus for discriminating a grinding state from a non-grinding state in a grinding machine wherein a workpiece is ground with a grinder, comprising:

• a plurality of vibration sensors including at least one acoustic-emission sensor, which detect vibrations of different frequency bands, respectively, which are produced during grinding of the workpiece by the grinder;
• and
• discriminating means for judging that the workpiece is being ground by the grinder when levels of output signals generated from at least two of said vibration sensors are higher than respective predetermined threshold levels, and for judging that the workpiece is not being ground by the grinder when the level of an output signal from less than two of said vibration sensors is higher than a predetermined threshold level.