18-10-2012, 04:48 PM
VIBRATION ANALYSIS TECHNIQUES FOR GEARBOX DIAGNOSTIC
VIBRATION ANALYSIS TECHNIQUES.pdf (Size: 384.04 KB / Downloads: 209)
ABSTRACT
Gears are important element in a variety of industrial applications such as machine tool and gearboxes. An unexpected
failure of the gear may cause significant economic losses. For that reason, fault diagnosis in gears has been the subject of
intensive research. Vibration signal analysis has been widely used in the fault detection of rotation machinery. The vibration
signal of a gearbox carries the signature of the fault in the gears, and early fault detection of the gearbox is possible by
analyzing the vibration signal using different signal processing techniques. In this paper, a review is made of some current
vibration analysis techniques used for condition monitoring in gear fault.
INTRODUCTION
All machines with moving parts give rise to sound
and vibration. Each machine has a specific vibration
signature related to the construction and the state of
the machine. If the state of the machine changes the
vibration signature will also change. A change in the
vibration signature can be used to detect incipient
defects before they become critical. This is the basics
of many condition monitoring methods. Condition
monitoring can save money through increased
maintenance efficiency and by reducing the risk of
serious accidents by preventing breakdowns. The use
of vibration analysis as one of the fundamental tools
for condition monitoring has been developed
extensively over a period of approximately 35 years.
Time Domain Analysis:
The time domain
methods try to analyze the amplitude and phase
information of the vibration time signal to detect the
fault of gear-rotor-bearing system. The time domain
is a perceptive that feels natural, and provides
physical insight into the vibration [6]. It is
particularly useful in analyzing impulsive signals
from bearing and gear defects with non-steady and
short transient impulses [7].
Time Waveform Analysis:
Prior to the
commercial availability of spectral analyzers, almost
all vibration analysis was performed in the time
domain. By studying the time domain waveform
using equipment such as oscilloscopes, oscillographs,
or ‘vibrographs’, it was often possible to detect
changes in the vibration signature caused by faults.
However, diagnosis of faults was a difficult task;
relating a change to a particular component required
the manual calculation of the repetition frequency
based on the time difference observed between
feature points. Waveform analysis can also be useful
in identify vibrations that are non synchronous with
shaft speed. In machine cost down analysis waveform
can indicate the occurrence of resonance. A typical
vibration waveform is shown in figure-3.1 for a
gearbox. This waveform shows the anomalous
behavior of the gear after certain intervals with large
magnitude. The peak level, RMS, level, and the crest
factor are often used to quantify the time signal.