Page 13 - Mechatronic Systems Modelling and Simulation with HDLs

2 1 OBJECTIVE AND MOTIVATION

This is particularly true if the simulation relates to the design of a technical system
and its task is to make predictions about the system’s functionality. In this case
the system in question does not exist at all in the real world, which means that no
measurements are available for checking the model. Rather, the design has yet to
be investigated and completed. So proving the correctness of a model is a matter
of importance. If we now interpret — as did Butterfield in [55] — a model as a
scientific theory, then the validation of the model must be placed within narrow
boundaries. According to Popper [338] the following is true for the validation of
a theory:

In order to be scientific, a theory must be falsifiable. It must be empirically testable,
at least in principle, and there must be a test that disproves the theory in the event
of a negative outcome.
There can never be a rigorous validation of a scientific theory. The best that we
can do is to develop empirical tests for the theory— fair tests, but the stricter the
better — and to hold onto the theory only as long as it has passed all tests.

The same applies for the validation of models. We can develop as many tests for a
model as we like, but this does not prove the validity of the model. At best, trust
in a model increases with the number of tests.
Depending upon the problem to be solved, we can differentiate between two fun-
damental starting points in the simulation of mechatronic systems. If the mechanical
part of a mechatronic system is to be developed, then the mechanics should be
developed taking into account the electronics. In this case electronics and software
are commonly considered as a regulatory function and dealt with along with the
mechanics in the form of suitable equations. The purpose of this work is to inves-
tigate the opposite case — the development of electronics and software taking into
account the mechanical component. This type of design should be supported by
simulations.
Hardware description languages, which have been widespread in the field of
electronics for some time, and for which various commercial simulators are already
available, represent the tools for achieving this end. Anything that can be modelled
using a hardware description language can also be simulated.
Thus the task is primarily a modelling problem. Furthermore, standards exist
for hardware description languages, which means that models can be exchanged
between simulators. One example is the IEEE standard VHDL 1076.1 (VHDL-
AMS) [160], which permits the description of digital and analogue systems. The
aim of this work is to cover the entire breadth of modelling for mechatronic and
micromechatronic systems using hardware description languages and to thereby
take a direct route to the corresponding simulations.
This structure of this work is as follows: After the introduction, the second
chapter deals with the principles of modelling and simulation for electronics and
mechanics. Particular importance is attributed to the verification and validation of
models. The third chapter describes state of the art techniques for the simulation