This study develops a micro-tool condition monitoring
system consisting of accelerometers on the spindle, a
data acquisition and signal transformation module, and a
backpropagation neural network. This study also discusses the
effect of the sensor installations, selected features, and the
bandwidth size of the features on the classification rate. To
collect the vibration signals necessary for training the system
model and verifying the system, an experiment was implemented
on a micro-milling research platform along with a
700 μm diameter micro-end mill and a SK2 workpiece. A
three-axis accelerometer was installed on a sensor plate
attached to the spindle housing to collect vibration signals in
three directions during cutting. The frequency domain features
representing changes in tool wear were selected based on the
class mean scatter criteria after transforming signals from the
time domain to the frequency domain by fast Fourier
transform. Using the appropriate vibration features, this study
develops and tests a backpropagation neural network classifier.
Results show that proper feature extraction for classification
provides a better solution than applying all spectral
features into the classifier. Selecting five features for
classification provides a better classification rate than the case
with four and three features along with the 30 Hz bandwidth
size of the spectral feature. Moreover, combining the signals
for tool condition from both direction signals provides a better
classification rate than determining the tool condition using a
one-direction single sensor