Failure Stage - Mitsubishi Electric FATEC FR-A800 Manual

1
IMPORTANCE OF PRODUCTIVE MAINTENANCE
1.6

Failure stage

Generally, complicated system failure is categorized into three stages, initial failure, random failure,
and wear-out failure as shown in Fig. 1.1. Initial failures are considered to be removed in
manufacturing and inspection processes by a manufacturer. Because random failures are
unforeseen and occur suddenly at any time within the useful life of equipment before it is worn, it is
difficult to take the technical measure. At present, the measure only based on the statistical treatment
can be taken.
Wear-out failures occur at nearly the end of useful life in the course of deterioration or as a result of
wear, and increase suddenly as time proceeds. At Point tb in Fig. 1.1 which means the replacement
years, preventive maintenance will be made proper by changing specific parts for new ones.
0
Early
failure
period
Random failure period
ta
Number of years of use
Fig. 1.1 Bath-tub curve
Wear-out
failure period
tb
1.6 Failure stage
1
2
3
4
5
6
7
8
5