Page 159 - Mechatronic Systems Modelling and Simulation with HDLs

148 7 MECHATRONICS

7.4 Demonstrator 3: Camera Winder

7.4.1 Introduction

The third example originates not from automotive engineering. It relates to a pho-
tographic camera with an external motor winder, which looks after the automatic
film movement. This system differs from the two other mechatronic examples
because, in this case, the electronics provides the drive and not only the control of
the system. Furthermore, at the time of the investigation not all components of the
system were available. Nevertheless, the system could still be investigated on this
basis, and this investigation yielded a significant foundation for the design deci-
sions under consideration. Thus the described approach is capable of supporting
the top-down design of mechatronic systems. The subject is also dealt with in Pelz
et al. [331] and Landt [213].
The model was set up for this system to illustrate a real system, the Leica R8,
together with its motor winder. At the time of modelling the winder was still at
the development stage. The main task was to maximise the number of pictures
that could be taken by a battery or rechargeable battery. Several motors were
investigated to this end; one of the candidates was not even in existence at the
time. All that was available for this motor was a set of parameters that had been
calculated and estimated in advance. One of the main questions was whether it
would be worthwhile to actually have this virtual motor developed. The gearbox
had to be set up for each motor in order to minimise the power consumption whilst
achieving the specified time for taking a picture.

7.4.2 System description
The system includes camera and motor winder and has an electronic and a mechan-
ical circuit. The electronics consists of a battery pack, the power transistors, the
associated control circuit and the electric motor, which is naturally also part of the
mechanics. This subsystem also comprises of a gearbox, a mechanical load and a
mechanical stop. The mechanical load represents the effect of friction when the
film is pulled out of its cartridge.
Figure 7.9 shows the (simplified) system structure, placing emphasis on the
mechanics and the interface between electronics and mechanics. Again, the simu-
lation is performed using an electronics simulator, which we can expect to correctly
process the electronics.

7.4.3 Modelling

Batteries and rechargeable batteries
The model of the battery or rechargeable battery pack is based upon measurements
of various brands and types. First a load cycle is defined that imitates the typical