Page 73 - Mechatronic Systems Modelling and Simulation with HDLs

62 3 MODELLING AND SIMULATION OF MIXED SYSTEMS

Micromechatronics

In [121] G¨ otz et al. produce a coupling between a finite element simulator and a
circuit simulator. The idea consists of calculating the deformation of a pressure
sensor structure using a finite element simulator and using the results to determine
changes of piezo resistances. The circuit simulator is then used to determine the
output of the read-out circuit. This consists primarily of a frequency modulation.
Using this process the mechanical structure can be optimised very simply. How-
ever, the feedback of the electronics on the mechanics and any dynamic effects of
the mechanics have not been taken into account.
A coupling between a FE simulator (ANSYS) for continuum mechanics and
the circuit simulator PSpice for analogue electronics is proposed by D¨ otzel and
Billep [86] and Klein et al. [198]. The applications used here are the simulation
of micromirrors [86] and force sensors [198]. However, details of the coupling are
not given in either case.

3.5.4 Evaluation

In simulator coupling the performance of the coupled tool is beneficial because
the optimal modelling method can be selected for each field. This reduces the
total modelling cost incurred, whilst the validation of the models can utilise the
results within the domain in question. Further domains can be taken into account
by linking in appropriate simulation tools. On the other hand, simulator coupling
leads to problems in the operation of the simulator package and in handling the
data flow at the interface. The simulators involved must be suitably synchronised
with one another. The simulation time is typically very high due to the necessary
iterations for each time interval. Finally, convergence problems may occur if there
is strong coupling between the subsystems.

3.6 Summary

Various approaches to the modelling and simulation of mechatronic and micro-
mechatronic systems have been considered in this chapter. We can differentiate
between three groups of methods: model transformation, modelling in a domain-
independent form, and simulator coupling. There are currently two options on
offer that allow us to cover the whole spectrum of analogue electronics, digital
electronics, software, multibody mechanics and continuum mechanics. These are
simulator coupling and the universal modelling in hardware description languages,
which will be described comprehensively in what follows.