Page 237 - Sensors and Control Systems in Manufacturing

Networking of Sensors and Contr ol Systems in Manufacturing

FIGURE 4.1 Flexible machining cell. 197

After the data have been distilled into information, the deductive
process begins, leading finally to the fault diagnosis. Expert systems
have been used effectively for diagnostic efforts, with the diagnostic
system presenting either a single diagnosis or a set of possibilities
with their respective probabilities, based on the a priori and a posteriori
information.

4.7.2 Resonance and Vibration Analysis
Resonance and vibration analysis is a proven method for diagnosing
deteriorating machine elements in steady-state process equipment
such as turbomachinery and fans. The effectiveness of resonance and
vibration analysis in diagnosing faults in machinery operating at
variable speed is not proven, but additional study has indicated good
potential for its application in robots. One difficulty with resonance
and vibration analysis is the attenuation of the signal as it travels
through a structure on the way to the sensors and transducers. More-
over, all motion of the machine contributes to the motion measured
by the sensors and transducers, so sensors and transducers must be
located as close as possible to the component of concern to maximize
the signal-to-noise ratio.

4.7.3 Sensing Motor Current for Signature Analysis
Electric motors generate back electromotive force (emf) when sub-
jected to mechanical load. This property makes a motor a transducer