Graphics Reference
In-Depth Information
We sometimes forget about this and discuss product reliability from the standpoint of
a user. Reliability Engineering of yesterday is based on statistics and it is developed
for the producer, not for the user. Products are reliable from the standpoint of the
producer. It does not guarantee reliability of an individual user's product.
Such an approach was effective yesterday, because products were produced in
mass and even if the product you were using might fail, you could replace it with
another one easily. We lived in a world of statistics.
2 Case of Mechanical Products
Traditionally break in was considered in mechanical engineering to be a phe-
nomenon to adjust moving parts and settle them down to a stable working condi-
tion. The period of decreasing failure rate of a bathtub curve corresponds to the
period of breaking in or running in of mechanical products. The period of breaking
in used to be long. With the progress of technology, this period becomes shorter and
shorter. But even if this period of breaking in can be made shorter, the bath tub
curve shows the failure rate of mass produced products. It does not mean that your
product keeps operating in a good condition.
Although a bath tub curve is very effective for electric products, situations are
different in mechanical products. And mass produced mechanical products do not
operate as electronic products do. Their operating conditions vary from product to
product. Thus, what a customer expects from mechanical products or machines are
very much different from those of electric products. The customer of mechanical
products would like their own product
to work well
in their own operating
conditions.
Let us take a passenger car for example. So many number of the same model was
produced yesterday. But people would like to drive as they like in their own
conditions. The road conditions, the environments, and even the traits of drivers
vary extensively. Thus, cars were certainly mass produced, but they were not driven
under the same conditions. Each car has its particular operating condition.
Yesterday, what people wanted was products. Getting the products they want
was their top priority and how they work was second or sometimes third.
We succeeded in making our products uniform but the operating conditions
remained very much diverse. But, such diversity of the operating conditions was
not too much of a problem these days because the quality improvements were so
rapid and so great that we were happy to get new better quality products, even
though they might not have worked good enough.
Engineers realized then that no matter how much they improve product quality,
products do not exhibit the true performance they design if the environmental
conditions were poor. So their next focus was to improve the environmental or
operating conditions. Thus, the environmental conditions improved very rapidly
and became uniform in a very short time.
