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7

Mechatronics

7.1 Modelling of Mechatronic Systems

The aim of this chapter is to apply the foundations obtained in previous chapters
to actual mechatronic systems. The interaction between the domains is particularly
significant here because the interfaces contribute significantly to system behaviour.
In particular, we are aiming too low if we only consider electronics or mechanics
independently of each other. The problem of the joint simulation of electronics and
mechanics must be solved, which again throws up a whole range of problems:
In the case of mechatronics, the time constants of mechanics and electronics
often differ by orders of magnitude. For macromechanics we can expect oscillations
of a few (tens of) hertz. In electronics the figure lies four to six orders of magnitude
higher. So we could assume that the dynamic interaction between electronics and
mechanics can be disregarded. The opposite is true. For example, a wide range
of control algorithms are performed on embedded controllers. Their running time
again lies in the millisecond range, so that dynamic feedback between electronics
and mechanics very definitely plays a role. This requires the dynamic simulation
of the entire system in order to be able to track cyclical dependencies, including
those that cross domain boundaries. Another reason for the importance of this is
the fact that domain boundaries often also represent the interfaces between design
teams working in parallel.
For the field of mechanics, precise models that are compatible with an electron-
ics simulator must be prepared. During the following chapter we will exclusively
consider multibody mechanics, which is generally sufficient for system consider-
ations in the field of macro mechatronics. Even with this limitation the vectorial
nature of mechanics is not easy to represent on a circuit simulator.
An efficient conversion is of crucial importance for the field of software in
particular. Millions of machine instructions are performed in a single second of
real time. On the other hand, it is necessary to precisely determine the timing of
the functions implemented using software, which requires a precise synchronisation
between software and electronics. This is indispensable in order to correctly reflect
the dynamics between software, electronics and mechanics.

Mechatronic Systems Georg Pelz
 2003 John Wiley & Sons, Ltd ISBN: 0-470-84979-7