  The importance of simulation at machine level in industrial environments is
steadily increasing especially in the design and commissioning phase. Using
models during the operation phase together with the real machine or plant is
referred to as online simulation. Online simulation is used for system
monitoring, predictive analyses, decision support or online optimization and
therefore has various advantages and a wide field of applications. This paper
has the aim to characterize online simulation at machine level in industrial
automation focusing on key technologies and common applications. Therefore, a
set of 65 relevant publications, which are focusing on this subject, is found
by database search, expert consultation, and snowballing. As key technological
aspects, the used model types, interfaces and platforms, and the aspects of
initialization and synchronization are further investigated. The results are
interpreted and limitations, knowledge gaps and future prospects are discussed.
The potential of online simulation at machine level especially arises due to
the increasing availability of component and machine models from the design and
commissioning phase, which can be reused for online simulation. Remaining
challenges are identified concerning implementation, simulation platforms,
model maintenance and especially in the field of synchronization.
