NC Machine Tools Fault Diagnosis Based on Kernel PCA and -Nearest Neighbor Using Vibration Signals

Table 1

Dimensionless statistical feature parameters.

Domain	Parameter	Formula	Remark
Time	Waveform		,
	Peak		,
	Kurtosis
	Where is a signal series for = 1, 2, …, , is the number of data points
Frequency	Stabilization ratio		,
	Wave-height ratio
	Power spectrum standard deviation		,
	Frequency high-low ratio		,
	Degree of irregular
	Where is the frequency signal with by Fast Fourier Transform (FFT) and is the power spectrum of