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Specification of Reactive Hardware/Software Systems - Electronic ...

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400 Case Study<br />

DISTR DISTR DISTR DISTR DISTR DISTR<br />

Feeder<br />

Sensors/<br />

Actuators<br />

Merger<br />

Sensors/<br />

Actuators<br />

DISTR<br />

Printer<br />

Separator_<br />

Sensors/<br />

Actuators<br />

DISTR<br />

Printer<br />

Separator_<br />

Sensors/<br />

Actuators<br />

Feeder<br />

Sensors/<br />

Actuators<br />

Feeder_<br />

Controller<br />

Merger_<br />

Controller<br />

Feeder_<br />

Controller<br />

Feeder_<br />

Controller<br />

Packer<br />

Sensors/<br />

Actuators<br />

Feeder_<br />

Controller<br />

Packer_<br />

Controller<br />

Product_<br />

Information_<br />

Server<br />

Printer/<br />

Separator<br />

Sensors/<br />

Actuators<br />

Separator<br />

/Printer_<br />

Controller<br />

DISTR,SEQ<br />

Figure 12.12: Instance Structure <strong>of</strong> Centralised Control System<br />

Stacker<br />

Sensors/<br />

Actuators<br />

Stacker_<br />

Controller<br />

Central_<br />

Control_<br />

Station<br />

But also a number <strong>of</strong> succeeding models were, and are still being, developed. During the<br />

modelling process it became apparent that the model presented in this chapter was too<br />

restrictive to fit in all necessary forms <strong>of</strong> behaviour. This was especially due to a number<br />

<strong>of</strong> architectural constraints, implementation constraints and mechanical constraints that<br />

had to be satisfied. It was typical that these constraints only became recognised after a<br />

substantial amount <strong>of</strong> modelling effort was spent. It seemed impossible to specify all<br />

constraints a priori, before any model was actually being built.<br />

Examples <strong>of</strong> some relevant problems we encountered are:<br />

The high speed <strong>of</strong> 20 thousand products per hour makes it impossible to instantly<br />

start and stop a transporter device. This fact violated the solution <strong>of</strong> creating<br />

completely independent stations running asynchronously at their own speed.<br />

There appeared to be a specific kind <strong>of</strong> feeder whose actions had to be scheduled<br />

before the involved product information had even entered the station. This fact<br />

violated the solution <strong>of</strong> letting the stations refer to only those product informations<br />

that correspond to mailing products contained in the station.<br />

Our most recent model solves many <strong>of</strong> the encountered constraints and problems. In<br />

order to protect the investment <strong>of</strong> the Buhrs company in this model it is not addressed<br />

in this thesis.

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