Page 147 - Mechatronic Systems Modelling and Simulation with HDLs

136 7 MECHATRONICS

In addition to the provision of the models and the dynamic simulation of a system
that goes beyond domain limits, the representation of the results can sometimes
be a problem. Of course, we always obtain the values of system variables plotted
against time, as is also normal for electronics simulation. In the case of mechanics,
however, we would often prefer an animation, in order to be able to evaluate the
system behaviour at a glance. As far as software is concerned, the typical outputs
of an electronics simulator are virtually useless. We would like a debugger, like
those used in pure software development, which illustrates the sequence of the
software and furthermore permits control of the sequence, perhaps by breakpoints.
As will be shown in what follows, the introduction of hardware description
languages into mechatronics lags behind that of microsystem technologies. A
significant reason for this is that microsystem technologies developed from micro-
electronics, so hardware description languages, which were initially developed for
microelectronics, were quickly implemented there too. By contrast, mechatronics
developed from mechanical engineering, where electronics is often reduced to con-
trol technology and can thus be considered using comparatively simple equations.
Recently, hardware description languages have also begun to be encountered in
mechatronics, with the automotive industry taking the lead.
The use of hardware description languages for the design of mechatronic systems
will be illustrated on the basis of four examples. These are a semi-active wheel
suspension system, an internal combustion engine with drive train, a camera winder
and a disk drive.

7.2 Demonstrator 1: Semi-Active Wheel
Suspension

7.2.1 System description

In what follows a semi-active wheel suspension will be described, see Hennecke
et al. [137] or [138], Duttlinger and Filsinger [89] or Roppenecker [352] for the
technical fundamentals. The idea of semi-active wheel suspension is that the sys-
tem adapts the parameters of shock absorbers or body springs to the current
road conditions and the corresponding driving situation. This is achieved by an
embedded processor, which means that electronics, mechanics and software have
to be considered at the same time here. The system described in what follows
reflects the concept of BMW’s ‘electronic damper control’, see [137] and [138]
and Figure 7.1. A similar system is also offered by Mercedes-Benz, see [89]. The
difference between semi-active and active wheel suspension is that, in the latter
case, forces can be applied by hydraulics, for example, in order to improve driving
safety and comfort. Put simply, the vehicle lifts one or more wheels up in order
to minimise the vertical movement of the body. This approach has, however, not
yet become prevalent for reasons of cost and energy.