  The need for maintenance is based on the wear of components of machinery. If
this need can be defined reliably beforehand so that no unpredicted failures
take place then the maintenance actions can be carried out economically with
mini-mum disturbances to production. There are two basic challenges in solving
the above. First understanding the development of wear and failures, and second
managing the measurement and diagnosis of such parameters that can reveal the
development of wear. In principle the development of wear and failures can be
predicted through monitoring time, load or wear as such. Moni-toring time is
not very efficient, as there are only limited numbers of components that suffer
from aging which as such is the result of chemical wear i.e. changes in the
material. In most cases the loading of components influences their wear. In
principle the loading can be stable or varying in nature. Of these two cases
the varying load case is much more challenging than the stable one. The
monitoring of wear can be done either directly e.g. optical methods or
indirectly e.g. vibration. Monitoring actual wear is naturally the most
reliable approach, but it often means that additional investments are needed.
The paper discusses how the monitoring of wear and need for maintenance can be
done based on the use of Cyber Physical Systems.
