Sensorless chatter detection

A sensorless machine tool chatter detection system, said system comprising:

• a machine tool configured for performing an operation on a workpiece;
• and
• a controller in communication with the machine tool, said controller being configured to detect chatter by performing steps including;
• determining if the machine tool is cutting material from the workpiece based on spindle torque command data;
• when the machine tool is not cutting material from the workpiece, storing a time segment of the spindle torque command data in an air-cut reference data set;
• when the machine tool is cutting material from the workpiece, converting the air-cut reference data set and the spindle torque command data to a frequency domain to create air-cut frequency data and torque command frequency data, respectively;
• spectrally subtracting a multiple of the air-cut frequency data from the torque command frequency data to produce filtered torque command data;
• downscaling the filtered torque command data at frequencies equal to integer multiples of a spindle speed;
• evaluating a plurality of chatter indicators at frequencies across a frequency spectrum, where a first indicator is a magnitude of the filtered torque command data, and a second indicator is a magnitude ratio of the filtered torque command data to the air-cut frequency data;
• and
• changing operating conditions of the machine tool when a comparison of the first and second indicators to predefined criteria indicates that chatter is occurring based on either indicator.