Page 28 - Mechatronic Systems Modelling and Simulation with HDLs

2.4 MODEL DEVELOPMENT 17

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aspects are bond graphs, block diagrams and Pr/T networks. As these descriptive
forms also permit a modelling of electro-mechanical systems, these are described in
detail in Chapter 3 as alternatives to modelling using hardware description languages.

Circuit diagrams

In the case of design using a circuit diagram editor, modelling is primarily used
for the derivation of a net list, which is used as a circuit model, incorporating the
component or gate models. This procedure is so simple and unproblematic that the
process of modelling a circuit is not generally perceived as such. Likewise, there
are not normally any problems with the validation of the circuit model. In the most
extreme case there may be verification problems with the program for deriving the
net list. The field of application is predominantly the development of analogue
circuits. Although digital circuits can also be developed using circuit diagrams, a
top-down design process is only possible using behavioural modelling based upon
hardware description languages.

State graphs
Digital systems can also be represented by state graphs with the system structure
then being stored on relatively abstract levels. The selection of the state transitions
is precisely specified by conditions. Furthermore, in state graphs only the structure
of the connections is necessary in order to characterise the model in question. Such
a model can, for example, be used for the specification of digital behaviour, but it
can also be translated into a programming or hardware description language and
then used directly for the design of software and hardware.

Multibody diagrams

Things are more complicated for multibody mechanics. Although the importance
of structural modelling is gaining increasing recognition here too, see for example
the work of Panreck [313], when drawing up the model equations it is often the
system as a whole that is considered rather than viewing it as a collection of
components. Only with the introduction of object-oriented modelling, see Otter
[308] or Kecskem´ ethy [185], does the structural modelling of multibody systems
also become more prevalent.

Finite elements

A particularly graphic form of structural modelling is to break down mechanical
structures into finite elements for the modelling of continuum mechanics. This is

1 Predicate/transition network.