Page 56 - Mechatronic Systems Modelling and Simulation with HDLs

3.3 MODEL TRANSFORMATION 45

With the exception of high-frequency circuits, electronics can be considered
exclusively in topographic form in the simulation. The precise geometry is unim-
portant or can be considered using simple parameters. This is not the case in
mechanics, where three components of translation and three components of rotation
have to be taken into account.
Furthermore, translation and rotation cannot be considered independently of one
another, as illustrated by gyroscopic forces such as the Coriolis force.
A whole range of reference systems are relevant to the description of position,
movement and acceleration. We have the inertial system and various fixed body
reference systems, the origins of which may lie approximately at the centre of
gravity or at the coupling points. In electronics there is only a reference voltage
(ground) as the ‘inertial system’, and voltage or current arrows as fixed-component
‘reference systems’.
In electronics, and in particular in microelectronics, we sometimes have some
tens of millions of components. In mechanics, at most, a few tens to a few hun-
dreds of basic elements, e.g. rigid bodies, joints, springs, etc. have to be taken
into account.
The movements of mechanical bodies are typically subject to a whole range of
limitations. Mechanical stops are one example. Springs can only be extended up to
a certain degree. Elastic bodies deform under the effects of force. Similar effects
can also be found in electronics but they are far less prominent than is the case
in mechanics.

3.3 Model Transformation

3.3.1 Introduction

We can now specify a class of simulators and use this as the basis for the description
of models in the other domains. In principle, the basic simulator should be sought
out on the basis of the focal point of the desired investigation. In what follows we
will describe approaches based upon circuit simulators, logic or Petri net simulators,
multibody simulators, and finite-element simulators.

3.3.2 Circuit simulation

Introduction

In a circuit simulator the formulation of transformed models classically takes place
in a hardware description language. This approach is the main theme of the present
work and will be described comprehensively in the following chapters. Alterna-
tively, it is also possible to draw up equivalent circuit diagrams for mechanical
components. We can initially differentiate between two possibilities here. Firstly,