Monitoring method and system for machine tool

A monitoring method for a machine tool to machine a workpiece, the monitoring method comprising:

• detecting a vibration signal of a spindle of the machine tool;
• obtaining a vibration feature value of the vibration signal, wherein obtaining the vibration feature value of the vibration signal comprises:
• acquiring a time-domain signal of the vibration signal with a sampling frequency;
• converting the time-domain signal into a frequency-domain signal;
• obtaining at least one vibration value corresponding to at least one frequency equal to N multiple of a fundamental frequency of the frequency-domain signal, wherein N is an integer of 1 or more;
• calculating a sum of the at least one vibration value;
• and
• determining whether an additional vibration value exists beyond the N multiple of the fundamental frequency, wherein the additional vibration value is greater than the vibration value corresponding to 1 multiple of the fundamental frequency;
• and
• if the additional vibration value exists, the vibration feature value equals the sum plus the additional vibration value;
• and
• if the additional vibration value does not exist, the vibration feature value equals the sum;
• determining whether the vibration feature value exceeds a threshold condition determined by a training model based on a predetermined surface quality of the workpiece, wherein the training model is trained with a machining quality database through a machine learning algorithm, and the machining quality database is established according to the following steps:
• detecting a sample vibration signal of the spindle of the machine tool when machining a specimen with a machining condition, wherein the machining condition comprises a spindle speed and a feed speed of the machine tool;
• obtaining a sample vibration feature value of the sample vibration signal;
• measuring a sample surface quality of the specimen under the machining condition;
• and
• recording the machining condition and the sample vibration feature value and the sample surface quality under the machining condition;
• and
• adjusting a machining parameter of the machine tool when the vibration feature value exceeds the threshold condition, wherein adjusting the machining parameter of the machine tool comprises obtaining an optimized spindle speed of the machine tool, and obtaining the optimized spindle speed of the machine tool comprises:
• setting a speed interval;
• iteratively executing the following steps with different spindle speeds within the speed interval:
• detecting a test vibration signal of the spindle of the machine tool when trial machining a test piece with a predetermined spindle speed;
• and
• obtaining a test vibration feature value of the test vibration signal;
• and
• determining the predetermined spindle speed corresponding to a minimum test vibration feature value as the optimized spindle speed.